path: root/doc/rfc/rfc8772.txt

Independent Submission                                             S. Hu
Request for Comments: 8772                                  China Mobile
Category: Informational                                  D. Eastlake 3rd
ISSN: 2070-1721                                   Futurewei Technologies
                                                                  F. Qin
                                                            China Mobile
                                                                 T. Chua
                                            Singapore Telecommunications
                                                                D. Huang
                                                                     ZTE
                                                                May 2020


The China Mobile, Huawei, and ZTE Broadband Network Gateway (BNG) Simple
          Control and User Plane Separation Protocol (S-CUSP)

Abstract

   A Broadband Network Gateway (BNG) in a fixed wireline access network
   is an Ethernet-centric IP edge router and the aggregation point for
   subscriber traffic.  Control and User Plane Separation (CUPS) for
   such a BNG improves flexibility and scalability but requires various
   communication between the User Plane (UP) and the Control Plane (CP).
   China Mobile, Huawei Technologies, and ZTE have developed a simple
   CUPS control channel protocol to support such communication: the
   Simple Control and User Plane Separation Protocol (S-CUSP).  S-CUSP
   is defined in this document.

   This document is not an IETF standard and does not have IETF
   consensus.  S-CUSP is presented here to make its specification
   conveniently available to the Internet community to enable diagnosis
   and interoperability.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8772.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
   2.  Terminology
     2.1.  Implementation Requirement Keywords
     2.2.  Terms
   3.  BNG CUPS Overview
     3.1.  BNG CUPS Motivation
     3.2.  BNG CUPS Architecture Overview
     3.3.  BNG CUPS Interfaces
       3.3.1.  Service Interface (Si)
       3.3.2.  Control Interface (Ci)
       3.3.3.  Management Interface (Mi)
     3.4.  BNG CUPS Procedure Overview
   4.  S-CUSP Protocol Overview
     4.1.  Control Channel Procedures
       4.1.1.  S-CUSP Session Establishment
       4.1.2.  Keepalive Timer and DeadTimer
     4.2.  Node Procedures
       4.2.1.  UP Resource Report
       4.2.2.  Update BAS Function on Access Interface
       4.2.3.  Update Network Routing
       4.2.4.  CGN Public IP Address Allocation
       4.2.5.  Data Synchronization between the CP and UP
     4.3.  Subscriber Session Procedures
       4.3.1.  Create Subscriber Session
       4.3.2.  Update Subscriber Session
       4.3.3.  Delete Subscriber Session
       4.3.4.  Subscriber Session Events Report
   5.  S-CUSP Call Flows
     5.1.  IPoE
       5.1.1.  DHCPv4 Access
       5.1.2.  DHCPv6 Access
       5.1.3.  IPv6 Stateless Address Autoconfiguration (SLAAC) Access
       5.1.4.  DHCPv6 and SLAAC Access
       5.1.5.  DHCP Dual-Stack Access
       5.1.6.  L2 Static Subscriber Access
     5.2.  PPPoE
       5.2.1.  IPv4 PPPoE Access
       5.2.2.  IPv6 PPPoE Access
       5.2.3.  PPPoE Dual-Stack Access
     5.3.  WLAN Access
     5.4.  L2TP
       5.4.1.  L2TP LAC Access
       5.4.2.  L2TP LNS IPv4 Access
       5.4.3.  L2TP LNS IPv6 Access
     5.5.  CGN (Carrier Grade NAT)
     5.6.  L3 Leased Line Access
       5.6.1.  Web Authentication
       5.6.2.  User Traffic Trigger
     5.7.  Multicast Service Access
   6.  S-CUSP Message Formats
     6.1.  Common Message Header
     6.2.  Control Messages
       6.2.1.  Hello Message
       6.2.2.  Keepalive Message
       6.2.3.  Sync_Request Message
       6.2.4.  Sync_Begin Message
       6.2.5.  Sync_Data Message
       6.2.6.  Sync_End Message
       6.2.7.  Update_Request Message
       6.2.8.  Update_Response Message
     6.3.  Event Message
     6.4.  Report Message
     6.5.  CGN Messages
       6.5.1.  Addr_Allocation_Req Message
       6.5.2.  Addr_Allocation_Ack Message
       6.5.3.  Addr_Renew_Req Message
       6.5.4.  Addr_Renew_Ack Message
       6.5.5.  Addr_Release_Req Message
       6.5.6.  Addr_Release_Ack Message
     6.6.  Vendor Message
     6.7.  Error Message
   7.  S-CUSP TLVs and Sub-TLVs
     7.1.  Common TLV Header
     7.2.  Basic Data Fields
     7.3.  Sub-TLV Format and Sub-TLVs
       7.3.1.  Name Sub-TLVs
       7.3.2.  Ingress-CAR Sub-TLV
       7.3.3.  Egress-CAR Sub-TLV
       7.3.4.  If-Desc Sub-TLV
       7.3.5.  IPv6 Address List Sub-TLV
       7.3.6.  Vendor Sub-TLV
     7.4.  Hello TLV
     7.5.  Keepalive TLV
     7.6.  Error Information TLV
     7.7.  BAS Function TLV
     7.8.  Routing TLVs
       7.8.1.  IPv4 Routing TLV
       7.8.2.  IPv6 Routing TLV
     7.9.  Subscriber TLVs
       7.9.1.  Basic Subscriber TLV
       7.9.2.  PPP Subscriber TLV
       7.9.3.  IPv4 Subscriber TLV
       7.9.4.  IPv6 Subscriber TLV
       7.9.5.  IPv4 Static Subscriber Detect TLV
       7.9.6.  IPv6 Static Subscriber Detect TLV
       7.9.7.  L2TP-LAC Subscriber TLV
       7.9.8.  L2TP-LNS Subscriber TLV
       7.9.9.  L2TP-LAC Tunnel TLV
       7.9.10. L2TP-LNS Tunnel TLV
       7.9.11. Update Response TLV
       7.9.12. Subscriber Policy TLV
       7.9.13. Subscriber CGN Port Range TLV
     7.10. Device Status TLVs
       7.10.1.  Interface Status TLV
       7.10.2.  Board Status TLV
     7.11. CGN TLVs
       7.11.1.  Address Allocation Request TLV
       7.11.2.  Address Allocation Response TLV
       7.11.3.  Address Renewal Request TLV
       7.11.4.  Address Renewal Response TLV
       7.11.5.  Address Release Request TLV
       7.11.6.  Address Release Response TLV
     7.12. Event TLVs
       7.12.1.  Subscriber Traffic Statistics TLV
       7.12.2.  Subscriber Detection Result TLV
     7.13. Vendor TLV
   8.  Tables of S-CUSP Codepoints
     8.1.  Message Types
     8.2.  TLV Types
     8.3.  TLV Operation Codes
     8.4.  Sub-TLV Types
     8.5.  Error Codes
     8.6.  If-Type Values
     8.7.  Access-Mode Values
     8.8.  Access Method Bits
     8.9.  Route-Type Values
     8.10. Access-Type Values
   9.  IANA Considerations
   10. Security Considerations
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   A Broadband Network Gateway (BNG) in a fixed wireline access network
   is an Ethernet-centric IP edge router and the aggregation point for
   subscriber traffic.  To provide centralized session management,
   flexible address allocation, high scalability for subscriber
   management capacity, and cost-efficient redundancy, the CU-separated
   (CP/UP-separated) BNG framework is described in a technical report
   [TR-384] from the Broadband Forum (BBF).  The CU-separated service
   CP, which is responsible for user access authentication and setting
   forwarding entries in UPs, can be virtualized and centralized.  The
   routing control and forwarding plane, i.e., the BNG UP (local), can
   be distributed across the infrastructure.  Other structures can also
   be supported, such as the CP and UP being virtual or both being
   physical.

   Note: In this document, the terms "user" and "subscriber" are used
   interchangeably.

   This document specifies the Simple CU Separation Protocol (S-CUSP)
   for communications over the BNG control channel between a BNG CP and
   a set of UPs.  S-CUSP is designed to be flexible and extensible so as
   to allow for easy addition of messages and data items, should further
   requirements be expressed in the future.

   This document is not an IETF standard and does not have IETF
   consensus.  S-CUSP was designed by China Mobile, Huawei Technologies,
   and ZTE.  It is presented here to make the S-CUSP specification
   conveniently available to the Internet community to enable diagnosis
   and interoperability.

   At the time of writing this document, the BBF is working to produce
   [WT-459], which will describe an architecture and requirements for a
   CP and UP separation of a disaggregated BNG.  Future work may attempt
   to show how the protocol described in this document addresses those
   requirements and may modify this specification to handle unaddressed
   requirements.

2.  Terminology

   This section specifies implementation requirement keywords and terms
   used in this document.  S-CUSP messages are described in this
   document using Routing Backus-Naur Form (RBNF) as defined in
   [RFC5511].

2.1.  Implementation Requirement Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  Terms

   This section specifies terms used in this document.

   AAA:         Authentication Authorization Accounting.

   ACK:         Acknowledgement message.

   BAS:         Broadband Access Server, also known as a BBRAS, BNG, or
                BRAS.

   BNG:         Broadband Network Gateway.  A BNG (or Broadband Remote
                Access Server (BRAS)) routes traffic to and from
                broadband remote access devices such as digital
                subscriber line access multiplexers (DSLAM) on an
                Internet Service Provider's (ISP) network.  BNG / BRAS
                can also be referred to as a BAS or BBRAS.

   BRAS:        Broadband Remote Access Server, also known as a BAS,
                BBRAS, or BNG.

   CAR:         Committed Access Rate.

   CBS:         Committed Burst Size.

   CGN:         Carrier Grade NAT.

   Ci:          Control Interface.

   CIR:         Committed Information Rate.

   CoA:         Change of Authorization.

   CP:          Control Plane.  CP is a user control management
                component that supports the management of the UP's
                resources such as the user entry and forwarding policy.

   CU:          Control Plane / User Plane.

   CUSP:        Control and User Plane Separation Protocol.

   DEI:         Drop Eligibility Indicator as defined in [802.1Q].  A
                bit in a VLAN tag after the priority and before the VLAN
                ID.  (This bit was formerly the CFI (Canonical Format
                Indicator).)

   DHCP:        Dynamic Host Configuration Protocol [RFC2131].

   dial-up:     This refers to the initial connection messages when a
                new subscriber appears.  The name is left over from when
                subscribers literally dialed up on a modem-equipped
                phone line but herein is applied to other initial
                connection techniques.  Initial connection is frequently
                indicated by the receipt of packets over PPPoE [RFC2516]
                or IPoE.

   EMS:         Element Management System.

   IPoE:        IP over Ethernet.

   L2TP:        Layer 2 Tunneling Protocol [RFC2661].

   LAC:         L2TP Access Concentrator.

   LNS:         L2TP Network Server.

   MAC:         48-bit Media Access Control address [RFC7042].

   MANO:        Management and Orchestration.

   Mi:          Management Interface.

   MSS:         Maximum Segment Size.

   MRU:         Maximum Receive Unit.

   NAT:         Network Address Translation [RFC3022].

   ND:          Neighbor Discovery.

   NFV:         Network Function Virtualization.

   NFVI:        NFV Infrastructure.

   PBS:         Peak Burst Size.

   PD:          Prefix Delegation.

   PIR:         Peak Information Rate.

   PPP:         Point-to-Point Protocol [RFC1661].

   PPPoE:       PPP over Ethernet [RFC2516].

   RBNF:        Routing Backus-Naur Form [RFC5511].

   RG:          Residential Gateway.

   S-CUSP:      Simple Control and User Plane Separation Protocol.

   Subscriber:  The remote user gaining network accesses via a BNG.

   Si:          Service Interface.

   TLV:         Type-Length-Value.  See Sections 7.1 and 7.3.

   UP:          User Plane.  UP is a network edge and user policy
                implementation component.  The traditional router's
                control plane and forwarding plane are both preserved on
                BNG devices in the form of a user plane.

   URPF:        Unicast Reverse Path Forwarding.

   User:        Equivalent to "customer" or "subscriber".

   VRF:         Virtual Routing and Forwarding.

3.  BNG CUPS Overview

3.1.  BNG CUPS Motivation

   The rapid development of new services, such as 4K TV, Internet of
   Things (IoT), etc., and increasing numbers of home broadband service
   users present some new challenges for BNGs such as:

   Low resource utilization:  The traditional BNG acts as both a gateway
      for user access authentication and accounting and also an IP
      network's Layer 3 edge.  The mutually affecting nature of the
      tightly coupled control plane and forwarding plane makes it
      difficult to achieve the maximum performance of either plane.

   Complex management and maintenance:  Due to the large numbers of
      traditional BNGs, configuring each device in a network is very
      tedious when deploying global service policies.  As the network
      expands and new services are introduced, this deployment mode will
      cease to be feasible as it is unable to manage services
      effectively and to rectify faults rapidly.

   Slow service provisioning:  The coupling of the CP and the forwarding
      plane, in addition to being a distributed network control
      mechanism, means that any new technology has to rely heavily on
      the existing network devices.

   The framework for a cloud-based BNG with CU separation to address
   these challenges for fixed networks is described in [TR-384].  The
   main idea of CU separation is to extract and centralize the user
   management functions of multiple BNG devices, forming a unified and
   centralized CP.  The traditional router's CP and forwarding plane are
   both preserved on BNG devices in the form of a UP.

3.2.  BNG CUPS Architecture Overview

   The functions in a traditional BNG can be divided into two parts: (1)
   the user access management function and (2) the routing function.
   The user access management function can be deployed as a centralized
   module or device, called the BNG Control Plane (BNG-CP).  The routing
   function, which includes routing control and the forwarding engine,
   can be deployed in the form of the BNG User Plane (BNG-UP).

   Figure 1 shows the architecture of a CU-separated BNG:

    +------------------------------------------------------------------+
    |        Neighboring policy and resource management systems        |
    |                                                                  |
    |   +-------------+   +-----------+   +---------+   +----------+   |
    |   | AAA Server  |   |DHCP Server|   |   EMS   |   |   MANO   |   |
    |   +-------------+   +-----------+   +---------+   +----------+   |
    +------------------------------------------------------------------+

    +------------------------------------------------------------------+
    |                       CU-separated BNG system                    |
    | +--------------------------------------------------------------+ |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |   | Address  |  |Subscriber| | AAA  ||Access||    UP     |   | |
    | |   |management|  |management| |      || mgt  ||management |   | |
    | |   +----------+  +----------+ +------++------++-----------+   | |
    | |                              CP                              | |
    | +--------------------------------------------------------------+ |
    |                                                                  |
    |                                                                  |
    |                                                                  |
    | +---------------------------+      +--------------------------+  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  | Routing control  |     |      |  | Routing control  |    |  |
    | |  +------------------+     | ...  |  +------------------+    |  |
    | |  +------------------+     |      |  +------------------+    |  |
    | |  |Forwarding engine |     |      |  |Forwarding engine |    |  |
    | |  +------------------+  UP |      |  +------------------+  UP|  |
    | +---------------------------+      +--------------------------+  |
   +------------------------------------------------------------------+

                Figure 1: Architecture of a CU-Separated BNG

   As shown in Figure 1, the BNG-CP could be virtualized and
   centralized, which provides benefits such as centralized session
   management, flexible address allocation, high scalability for
   subscriber management capacity, cost-efficient redundancy, etc.  The
   functional components inside the BNG-CP can be implemented as Virtual
   Network Functions (VNFs) and hosted in an NFVI.

   The UP management module in the BNG-CP centrally manages the
   distributed BNG-UPs (e.g., load balancing), as well as the setup,
   deletion, and maintenance of channels between CPs and UPs.  Other
   modules in the BNG-CP, such as address management, AAA, etc., are
   responsible for the connection with external subsystems in order to
   fulfill those services.  Note that the UP SHOULD support both
   physical and virtual network functions.  For example, network
   functions related to BNG-UP L3 forwarding can be disaggregated and
   distributed across the physical infrastructure, and the other CP
   management functions in the CU-separated BNG can be moved into the
   NFVI for virtualization [TR-384].

   The details of the CU-separated BNG's function components are as
   follows:

   The CP is responsible for the following:

   *  Address management: Unified address pool management and CGN
      subscriber address traceability management.

   *  AAA: This component performs Authentication, Authorization, and
      Accounting, together with RADIUS/Diameter.  The BNG communicates
      with the AAA server to check whether the subscriber who sent an
      access request has network access authority.  Once the subscriber
      goes online, this component (together with the Service Control
      component) implements accounting, data capacity limitation, and
      QoS enforcement policies.

   *  Subscriber management: User entry management and forwarding policy
      management.

   *  Access management: Process user dial-up packets, such as PPPoE,
      DHCP, L2TP, etc.

   *  UP management: Management of UP interface status and the setup,
      deletion, and maintenance of channels between CP and UP.

   The UP is responsible for the following:

   *  Routing control functions: Responsible for instantiating routing
      forwarding plane (e.g., routing, multicast, MPLS, etc.).

   *  Routing and service forwarding plane functions: Responsibilities
      include traffic forwarding, QoS, and traffic statistics
      collection.

   *  Subscriber detection: Responsible for detecting whether a
      subscriber is still online.

3.3.  BNG CUPS Interfaces

   The three interfaces defined below support the communication between
   the CP and UP.  These are referred to as the Service Interface (Si),
   Control Interface (Ci), and Management Interface (Mi) as shown in
   Figure 2.

             +-----------------------------------+
             |                                   |
             |               BNG-CP              |
             |                                   |
             +--+--------------+--------------+--+
                |              |              |
     1. Service |   2. Control | 3. Management|
      Interface |    Interface |    Interface |
           (Si) |         (Ci) |         (Mi) |
                |              |              |
                |           ___|___           |
                |       ___(       )___       |
               _|______(               )______|_
              (                                 )
             (         Network/Internet         )
              (________                 ________)
                |      (___         ___)      |
                |          (_______)          |
                |              |              |
                |              |              |
             +--+--------------+--------------+--+
             |                                   |
             |               BNG-UP              |
             |                                   |
             +-----------------------------------+

           Figure 2: Interfaces between the CP and UP of the BNG

3.3.1.  Service Interface (Si)

   For a traditional BNG (without CU separation), the user dial-up
   signals are terminated and processed by the CP of a BNG.  When the CP
   and UP of a BNG are separated, there needs to be a way to relay these
   signals between the CP and the UP.

   The Si is used to establish tunnels between the CP and UP.  The
   tunnels are responsible for relaying the PPPoE-, IPoE-, and L2TP-
   related control packets that are received from a Residential Gateway
   (RG) over those tunnels.  An appropriate tunnel type is Virtual
   eXtensible Local Area Network (VXLAN) [RFC7348].

   The detailed definition of Si is out of scope for this document.

3.3.2.  Control Interface (Ci)

   The CP uses the Ci to deliver subscriber session states, network
   routing entries, etc., to the UP (see Section 6.2.7).  The UP uses
   this interface to report subscriber service statistics, subscriber
   detection results, etc., to the CP (see Sections 6.3 and 6.4).  A
   carrying protocol for this interface is specified in this document.

3.3.3.  Management Interface (Mi)

   The Network Configuration Protocol (NETCONF) [RFC6241] is the
   protocol used on the Mi between a CP and UP.  It is used to configure
   the parameters of the Ci, Si, access interfaces, and QoS/ACL
   Templates.  It is expected that implementations will make use of
   existing YANG models where possible but that new YANG models specific
   to S-CUSP will need to be defined.  The definitions of the parameters
   that can be configured are out of scope for this document.

3.4.  BNG CUPS Procedure Overview

   The following numbered sequences (Figure 3) give a high-level view of
   the main BNG CUPS procedures.

      RG              UP                      CP              AAA
      |               |Establish S-CUSP Channel|               |
      |              1|<---------------------->|               |
      |               |                        |               |
      |               | Report board interface |               |
      |               |      information       |               |
      |              2|------to CP via Ci----->|               |
      |               |                        |               |
      |               |  Update BAS function   |               |
      |              3|    request/response    |               |
      |               |<-----on UP via Ci----->|               |
      |               |                        |               |
      |               | Update network routing |               |
      |               |    request/response    |               |
      |              4|<------- via Ci-------->|               |
      |  Online Req   |                        |               |
   5.1|-------------->|                        |               |
      |               | Relay the Online Req   |               |
      |            5.2|-----to CP via Si------>| Authentication|
      |               |                        |    Req/Rep    |
      |               |                     5.3|<------------->|
      |               | Send the Online Rep    |               |
      |            5.4|<----to UP via Si-------|               |
      |               |                        |               |
      |               | Create subscriber      |               |
      |               |    session on UP       |               |
      |            5.5|<--------via Ci-------->|               |
      |  Online Rep   |                        |               |
   5.6|<--------------|                        |               |
      |               |                        |  CoA Request  |
      |               |                     6.1|<--------------|
      |               | Update session on UP   |               |
      |            6.2|<--------via Ci-------->|               |
      |               |                        |  CoA Response |
      |  Offline Req  |                     6.3|-------------->|
   7.1|-------------->|                        |               |
      |               | Relay the Offline Req  |               |
      |            7.2|------to CP via Si----->|               |
      |               |                        |               |
      |               | Send the Offline Rep   |               |
      |            7.3|<-----to UP via Si------|               |
      |  Offline Rep  |                        |               |
   7.4|<--------------|                        |               |
      |               | Delete session on UP   |               |
      |            7.5|<--------via Ci-------->|               |
      |               |                        |               |
      |               |      Event report      |               |
      |              8|---------via Ci-------->|               |
      |               |                        |               |
      |               | Data synchronization   |               |
      |              9|<--------via Ci-------->|               |
      |               |                        |               |
      |               | CGN address allocation |               |
      |             10|<--------via Ci-------->|               |
      |               |                        |               |

                   Figure 3: BNG CUPS Procedures Overview

   (1)   S-CUSP session establishment: This is the first step of the BNG
         CUPS procedures.  Once the Ci parameters are configured on a
         UP, it will start to set up S-CUSP sessions with the specified
         CPs.  The detailed definition of S-CUSP session establishment
         can be found in Section 4.1.1.

   (2)   Board and interface report: Once the S-CUSP session is
         established between the UP and a CP, the UP will report status
         information on the boards and subscriber-facing interfaces of
         this UP to the CP.  A board can also be called a Line/Service
         Process Unit (LPU/SPU) card.  The subscriber-facing interfaces
         refer to the interfaces that connect the access network nodes
         (e.g., Optical Line Terminal (OLT), DSLAM, etc.).  The CP can
         use this information to enable the Broadband Access Server
         (BAS) function (e.g., IPoE, PPPoE, etc.) on the specified
         interfaces.  See Sections 4.2.1 and 7.10 for more details on
         resource reporting.

   (3)   BAS function enable: To enable the BAS function on the
         specified interfaces of a UP.

   (4)   Subscriber network route advertisement: The CP will allocate
         one or more IP address blocks to a UP.  Each address block
         contains a series of IP addresses.  Those IP addresses will be
         allocated to subscribers who are dialing up from the UP.  To
         enable other nodes in the network to learn how to reach the
         subscribers, the CP needs to notify the UP to advertise to the
         network the routes that can reach those IP addresses.

   (5)   5.1-5.6 is a complete call flow of a subscriber dial-up (as
         defined in Section 4.3.1) process.  When a UP receives a dial-
         up request, it will relay the request packet to a CP through
         the Si.  The CP will parse the request.  If everything is OK,
         it will send an authentication request to the AAA server to
         authenticate the subscriber.  Once the subscriber passes the
         authentication, the AAA server will return a positive response
         to the CP.  Then the CP will send the dial-up response packet
         to the UP, and the UP will forward the response packet to the
         subscriber (RG).  At the same time, the CP will create a
         subscriber session on the UP, enabling the subscriber to access
         the network.  For different access types, the process may be a
         bit different, but the high-level process is similar.  For each
         access type, the detailed process can be found in Section 5.

   (6)   6.1-6.3 is the sequence when updating an existing subscriber
         session.  The AAA server initiates a Change of Authorization
         (CoA) and sends the CoA to the CP.  The CP will then update the
         session according to the CoA.  See Section 4.3.2 for more
         detail on CP messages updating UP tables.

   (7)   7.1-7.5 is the sequence for deleting an existing subscriber
         session.  When a UP receives an Offline Request, it will relay
         the request to a CP through the Si.  The CP will send back a
         response to the UP through the Si.  The UP will then forward
         the Offline Response to the subscriber.  Then the CP will
         delete the session on the UP through the Ci.

   (8)   Event reports include the following two parts (more detail can
         be found in Section 4.3.4).  Both are reported using the Event
         message:

            8.1.  Subscriber Traffic Statistics Report

            8.2.  Subscriber Detection Result Report

   (9)   Data synchronization: See Section 4.2.5 for more detail on CP
         and UP synchronization.

   (10)  CGN address allocation: See Section 4.2.4 for more detail on
         CGN address allocation.

4.  S-CUSP Protocol Overview

4.1.  Control Channel Procedures

4.1.1.  S-CUSP Session Establishment

   A UP is associated with a CP and is controlled by that CP.  In the
   case of a hot-standby or cold-standby, a UP is associated with two
   CPs: the master CP and standby CP.  The association between a UP and
   its CPs is implemented by dynamic configuration.

   Once a UP knows its CPs, the UP starts to establish S-CUSP sessions
   with those CPs, as shown in Figure 4.

                    UP                               CP
                    |   TCP Session Establishment     |
                    |<------------------------------->|
                    |                                 |
                    |   Hello (version, capability)   |
                    |-------------------------------->|
                    |                                 |
                    |   Hello (version, capability)   |
                    |<--------------------------------|
                    |                                 |

                   Figure 4: S-CUSP Session Establishment

   The S-CUSP session establishment consists of two successive steps:

   (1)  Establishment of a TCP connection (3-way handshake) [RFC793]
        between the CP and the UP using a configured port from the
        dynamic port range (49152-65535).

   (2)  Establishment of an S-CUSP session over the TCP connection.

   Once the TCP connection is established, the CP and the UP initialize
   the S-CUSP session, during which the version and Keepalive timers are
   negotiated.

   The version information (Hello TLV, see Section 7.4) is carried
   within Hello messages (see Section 6.2.1).  A CP can support multiple
   versions, but a UP can only support one version; thus the version
   negotiation is based on whether a version can be supported by both
   the CP and the UP.  If a CP or UP receives a Hello message that does
   not indicate a version supported by both, it responds with a Hello
   message containing an Error Information TLV to notify the peer of the
   Version-Mismatch error, and the session establishment phase fails.

   Keepalive negotiation is performed by carrying a Keepalive TLV in the
   Hello message.  The Keepalive TLV includes a Keepalive timer and
   DeadTimer field.  The CP and UP have to agree on the Keepalive Timer
   and DeadTimer.  Otherwise, a subsequent Hello message with an Error
   Information TLV will be sent to its peer, and the session
   establishment phase fails.

   The S-CUSP session establishment phase fails if the CP or UP disagree
   on the version and keepalive parameters or if one of the CP or UP
   does not answer after the expiration of the Establishment timer.
   When the S-CUSP session establishment fails, the TCP connection is
   promptly closed.  Successive retries are permitted, but an
   implementation SHOULD make use of an exponential backoff session
   establishment retry procedure.

   The S-CUSP session timer values that need to be configured are
   summarized in Table 1.

        +---------------------+------------------+---------------+
        | Timer Name          | Range in Seconds | Default Value |
        +=====================+==================+===============+
        | Establishment Timer | 1-32767          | 45            |
        +---------------------+------------------+---------------+
        | Keepalive Timer     | 0-255            | 30            |
        +---------------------+------------------+---------------+
        | DeadTimer           | 1-32767          | 4 * Keepalive |
        +---------------------+------------------+---------------+

                      Table 1: S-CUSP Session Timers

4.1.2.  Keepalive Timer and DeadTimer

   Once an S-CUSP session has been established, a UP or CP may want to
   know that its S-CUSP peer is still connected.

   Each end of an S-CUSP session runs a Keepalive timer.  It restarts
   the timer every time it sends a message on the session.  When the
   timer expires, it sends a Keepalive message.  Thus, a message is
   transmitted at least as often as the value to which the Keepalive
   timer is reset, unless, as explained below, that value is the special
   value zero.

   Each end of an S-CUSP session also runs a DeadTimer and restarts that
   DeadTimer whenever a message is received on the session.  If the
   DeadTimer expires at an end of the session, that end declares the
   session dead and the session will be closed, unless their DeadTimer
   is set to the special value zero, in which case the session will not
   time out.

   The minimum value of the Keepalive timer is 1 second, and it is
   specified in units of 1 second.  The RECOMMENDED default value is 30
   seconds.  The recommended default for the DeadTimer is four times the
   value of the Keepalive timer used by the remote peer.  As above, the
   timers may be disabled by setting them to zero.

   The Keepalive timer and DeadTimer are negotiated through the
   Keepalive TLV carried in the Hello message.

4.2.  Node Procedures

4.2.1.  UP Resource Report

   Once an S-CUSP session has been established between a CP and a UP,
   the UP reports the state information of the boards and access-facing
   interfaces on the UP to the CP, as shown in Figure 5.  Report
   messages are unacknowledged and are assumed to be delivered because
   the session runs over TCP.

   The CP can use that information to activate/enable the BAS functions
   (e.g., IPoE, PPPoE, etc.) on the specified interfaces.

   In addition, the UP resource report may trigger a UP warm-standby
   process.  In the case of warm-standby, a failure on a UP may trigger
   the CP to start a warm-standby process, by moving the online
   subscriber sessions to a standby UP and then directing the affected
   subscribers to access the Internet through the standby UP.

                        UP                      CP
                        |  Report Board Status   |
                        |------to CP via Ci----->|
                        |                        |
                        | Report Interface Status|
                        |------to CP via Ci----->|
                        |                        |

                  Figure 5: UP Board and Interface Report

   Board status information is carried in the Board Status TLV
   (Section 7.10.2), and interface status information is carried in the
   Interface Status TLV (Section 7.10.1).  Both Board Status and
   Interface Status TLVs are carried in the Report message
   (Section 6.4).

4.2.2.  Update BAS Function on Access Interface

   Once the CP collects the interface status of a UP, it will
   activate/deactivate/modify the BAS functions on specified interfaces
   through the Update_Request and Update_Response message exchanges
   (Section 6.2), carrying the BAS Function TLV (Section 7.7).

                        UP                       CP
                        |   Update BAS Function   |
                        |         Request         |
                        |<-----on UP via Ci-------|
                        |                         |
                        |   Update BAS Function   |
                        |         Response        |
                        |------on UP via Ci------>|
                        |                         |

                       Figure 6: Update BAS Function

4.2.3.  Update Network Routing

   The CP will allocate one or more address blocks to a UP.  Each
   address block contains a series of IP addresses.  Those IP addresses
   will be assigned to subscribers who are dialing up to the UP.  To
   enable the other nodes in the network to learn how to reach the
   subscribers, the CP needs to install the routes on the UP and notify
   the UP to advertise the routes to the network.

                        UP                       CP
                        | Subscriber network route|
                        |      update request     |
                        |<------- via Ci----------|
                        |                         |
                        | Subscriber network route|
                        |      update response    |
                        |-------- via Ci--------->|
                        |                         |

                      Figure 7: Update Network Routing

   The Update_Request and Update_Response message exchanges, carrying
   the IPv4/IPv6 Routing TLVs (Section 7.8), update the subscriber's
   network routing information.

4.2.4.  CGN Public IP Address Allocation

   The following sequences (Figure 8) describe the procedures related to
   CGN address management.  Three independent procedures are defined:
   one each for CGN address allocation request/response, CGN address
   renewal request/response, and CGN address release request/response.

   CGN address allocation/renew/release procedures are designed for the
   case where the CGN function is running on the UP.  The UP has to map
   the subscriber private IP addresses to public IP addresses, and such
   mapping is performed by the UP locally when a subscriber dials up.
   That means the UP has to ask for public IPv4 address blocks for CGN
   subscribers from the CP.

   In addition, when a public IP address is allocated to a UP, there
   will be a lease time (e.g., one day).  Before the lease time expires,
   the UP can ask for renewal of the IP address lease from the CP.  It
   is achieved by the exchange of the Addr_Renew_Req and Addr_Renew_Ack
   messages.

   If the public IP address will not be used anymore, the UP SHOULD
   release the address by sending an Addr_Release_Req message to the CP.

   If the CP wishes to withdraw addresses that it has previously leased
   to a UP, it uses the same procedures as above.  The Oper code (see
   Section 7.1) in the IPv4/IPv6 Routing TLV (see Section 7.8)
   determines whether the request is an update or withdraw.

   The relevant messages are defined in Section 6.5.

                    UP                       CP
                    | CGN Address Allocation  |
                    |         Request         |
                 1.1|-------- via Ci--------->|
                    | CGN Address Allocation  |
                    |         Response        |
                 1.2|<------- via Ci----------|
                    |                         |
                    | CGN Address Renew       |
                    |         Request         |
                 2.1|-------- via Ci--------->|
                    | CGN Address Renew       |
                    |         Response        |
                 2.2|<------- via Ci----------|
                    |                         |
                    | CGN Address Release     |
                    |         Request         |
                 3.1|-------- via Ci--------->|
                    | CGN Address Release     |
                    |         Response        |
                 3.3|<------- via Ci----------|
                    |                         |

                 Figure 8: CGN Public IP Address Allocation

4.2.5.  Data Synchronization between the CP and UP

   For a CU-separated BNG, the UP will continue to function using the
   state that has been installed in it even if the CP fails or the
   session between the UP and CP fails.

   Under some circumstances, it is necessary to synchronize state
   between the CP and UP, for example, if a CP fails and the UP is
   switched to a different CP.

   Synchronization includes two directions.  One direction is from UP to
   CP; in that case, the synchronization information is mainly about the
   board/interface status of the UP.  The other direction is from CP to
   UP; in that case, the subscriber sessions, subscriber network routes,
   L2TP tunnels, etc., will be synchronized to the UP.

   The synchronization is triggered by a Sync_Request message, to which
   the receiver will (1) reply with a Sync_Begin message to notify the
   requester that synchronization will begin and (2) then start the
   synchronization using the Sync_Data message.  When synchronization
   finishes, a Sync_End message will be sent.

   Figure 9 shows the process of data synchronization between a UP and a
   CP.

                        UP                       CP
                        | Synchronization Request |
                        |<------- via Ci----------|
                        |                         |
                        | Synchronization Begin   |
                        |-------- via Ci--------->|
                        |                         |
                        | Board/Interface Report  |
                        |-------- via Ci--------->|
                        |                         |
                        | Synchronization End     |
                        |-------- via Ci--------->|
                        |                         |
                       1) Synchronization from UP to CP

                        UP                       CP
                        | Synchronization Request |
                        |-------- via Ci--------->|
                        |                         |
                        | Synchronization Begin   |
                        |<-------- via Ci---------|
                        |                         |
                        |      Synchronizes       |
                        |Subscriber Session States|
                        |  Network Route Entries  |
                        |<------- via Ci----------|
                        |                         |
                        | Synchronization End     |
                        |<-------- via Ci---------|
                        |                         |
                       2) Synchronization from CP to UP

                       Figure 9: Data Synchronization

4.3.  Subscriber Session Procedures

   A subscriber session consists of a set of forwarding states,
   policies, and security rules that are applied to the subscriber.  It
   is used for forwarding subscriber traffic in a UP.  To initialize a
   session on a UP, a collection of hardware resources (e.g., NP, TCAM,
   etc.) has to be allocated to a session on a UP as part of its
   initiation.

   Procedures related to subscriber sessions include subscriber session
   creation, update, deletion, and statistics reporting.  The following
   subsections give a high-level view of the procedures.

4.3.1.  Create Subscriber Session

   The sequence below (Figure 10) describes the DHCP IPv4 dial-up
   process.  It is an example that shows how a subscriber session is
   created.  (An example for IPv6 appears in Section 5.1.2.)

        RG              UP                       CP             AAA
        | Online Request|                        |               |
       1|-------------->|                        |               |
        |               |Relay the Online Request|               |
        |              2|-----to CP via Si------>| Authentication|
        |               |                        |    Req/Rep    |
        |               |                       3|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              4|<--------via Ci---------|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              5|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                       6|<------------->|
        |               |  Send Online Response  |               |
        |              7|<----to UP via Si-------|               |
        |               |                        |               |
        |Online Response|                        |               |
       8|<--------------|                        |               |
        |               |                        |               |

                  Figure 10: Creating a Subscriber Session

   The request starts from an Online Request message (step 1) from the
   RG (for example, a DHCP Discovery packet).  When the UP receives the
   Online Request from the RG, it will tunnel the Online Request to the
   CP through the Si (step 2).  A tunneling technology implements the
   Si.

   When the CP receives the Online Request from the UP, it will send an
   authentication request to the AAA server to authenticate and
   authorize the subscriber (step 3).  When a positive reply is received
   from the AAA server, the CP starts to create a subscriber session for
   the request.  Relevant resources (e.g., IP address, bandwidth, etc.)
   will be allocated to the subscriber.  Policies and security rules
   will be generated for the subscriber.  Then the CP sends a request to
   create a session to the UP through the Ci (step 4), and a response is
   expected from the UP to confirm the creation (step 5).

   Finally, the CP will notify the AAA server to start accounting (step
   6).  At the same time, an Online Response message (for example, a
   DHCP Ack packet) will be sent to the UP through the Si (step 7).  The
   UP will then forward the Online Response to the RG (step 8).

   That completes the subscriber activation process.

4.3.2.  Update Subscriber Session

   The following numbered sequence (Figure 11) shows the process of
   updating the subscriber session.

               UP                       CP             AAA
               |                        |  CoA Request  |
               |                       1|<--------------|
               | Session Update Request |               |
              2|<--------via Ci---------|               |
               |                        |               |
               | Session Update Response|               |
              3|---------via Ci-------->|               |
               |                        |  CoA Response |
               |                       4|-------------->|
               |                        |               |

                  Figure 11: Updating a Subscriber Session

   When a subscriber session has been created on a UP, there may be
   requirements to update the session with new parameters (e.g.,
   bandwidth, QoS, policies, etc.).

   This procedure is triggered by a Change of Authorization (CoA)
   request message sent by the AAA server.  The CP will update the
   session on the UP according to the new parameters through the Ci.

4.3.3.  Delete Subscriber Session

   The call flow below shows how S-CUSP deals with a subscriber Offline
   Request.

              RG               UP                       CP
               |Offline Request |                        |
              1|--------------->|                        |
               |                |    Relay the Offline   |
               |                |        Request         |
               |               2|------to CP via Si----->|
               |                |                        |
               |                |    Send the Offline    |
               |                |        Response        |
               |               3|<-----to UP via Si------|
               |Offline Response|                        |
              4|<---------------|                        |
               |                |     Session Delete     |
               |                |        Request         |
               |                |<--------via Ci---------|
               |                |     Session Delete     |
               |                |       Response         |
               |                |---------via Ci-------->|
               |                |                        |

                  Figure 12: Deleting a Subscriber Session

   Similar to the session creation process, when a UP receives an
   Offline Request from an RG, it will tunnel the request to a CP
   through the Si.

   When the CP receives the Offline Request, it will withdraw/release
   the resources (e.g., IP address, bandwidth) that have been allocated
   to the subscriber.  It then sends a reply to the UP through the Si,
   and the UP will forward the reply to the RG.  At the same time, it
   will delete all the status of the session on the UP through the Ci.

4.3.4.  Subscriber Session Events Report

                        UP                       CP
                        | Statistic/Detect Report|
                        |---------via Ci-------->|
                        |                        |

                          Figure 13: Events Report

   When a session is created on a UP, the UP will periodically report
   statistics information and subscriber detection results of the
   session to the CP.

5.  S-CUSP Call Flows

   The subsections below give an overview of various "dial-up"
   interactions over the Si followed by an overview of the setting of
   information in the UP by the CP using S-CUSP over the Ci.

   S-CUSP messages are described in this document using Routing Backus
   Naur Form (RBNF) as defined in [RFC5511].

5.1.  IPoE

5.1.1.  DHCPv4 Access

   The following sequence (Figure 14) shows detailed procedures for
   DHCPv4 access.

        RG              UP                       CP             AAA
        | DHCP Discovery|                        |               |
       1|-------------->|                        |               |
        |               |Relay the DHCP Discovery|               |
        |              2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                       3|<------------->|
        |               |  Send the DHCP Offer   |               |
        |              4|<----to UP via Si-------|               |
        |  DHCP Offer   |                        |               |
       5|<--------------|                        |               |
        |  DHCP Request |                        |               |
       6|-------------->|                        |               |
        |               | Relay the DHCP Request |               |
        |              7|-----to CP via Si------>|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              8|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              9|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      10|<------------->|
        |               |  Send DHCP ACK         |               |
        |             11|<----to UP via Si-------|               |
        |               |                        |               |
        |  DHCP ACK     |                        |               |
      12|<--------------|                        |               |
        |               |                        |               |

                          Figure 14: DHCPv4 Access

   S-CUSP implements steps 8 and 9.

   After a subscriber is authenticated and authorized by the AAA server,
   the CP creates a new subscriber session on the UP.  This is achieved
   by sending an Update_Request message to the UP.

   The format of the Update_Request message is shown as follows using
   RBNF:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   The UP will reply with an Update_Response message.  The format of the
   Update_Response message is as follows:

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

5.1.2.  DHCPv6 Access

   The following sequence (Figure 15) shows detailed procedures for
   DHCPv6 access.

        RG              UP                       CP             AAA
        |  Solicit      |                        |               |
       1|-------------->|                        |               |
        |               |  Relay the Solicit     |               |
        |              2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                       3|<------------->|
        |               |  Send the Advertise    |               |
        |              4|<----to UP via Si-------|               |
        |  Advertise    |                        |               |
       5|<--------------|                        |               |
        |               |                        |               |
        |  Request      |                        |               |
       6|-------------->|                        |               |
        |               |  Relay the Request     |               |
        |              7|-----to CP via Si------>|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              8|<--------via Ci-------->|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              9|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      10|<------------->|
        |               |  Send Reply            |               |
        |             11|<----to UP via Si-------|               |
        |  Reply        |                        |               |
      12|<--------------|                        |               |
        |               |                        |               |

                          Figure 15: DHCPv6 Access

   Steps 1-7 are a standard DHCP IPv6 access process.  The subscriber
   creation is triggered by a DHCP IPv6 request message.  When this
   message is received, it means that the subscriber has passed the AAA
   authentication and authorization.  Then the CP will create a
   subscriber session on the UP.  This is achieved by sending an
   Update_Request message to the UP (step 8).

   The format of the Update_Request message is as follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   The UP will reply with an Update_Response message (step 9).  The
   format of the Update_Response message is as follows:

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.1.3.  IPv6 Stateless Address Autoconfiguration (SLAAC) Access

   The following flow (Figure 16) shows the IPv6 SLAAC access process.

        RG              UP                       CP             AAA
        |      RS       |                        |               |
       1|-------------->|                        |               |
        |               |  Relay the Router      |               |
        |               |    Solicit (RS)        |               |
        |              2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                       3|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              4|<--------via Ci---------|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              5|---------via Ci-------->|               |
        |               |                        |               |
        |               |  Send Router Advertise |               |
        |               |         (RA)           |               |
        |              6|<----to UP via Si-------|               |
        |      RA       |                        |               |
       7|<--------------|                        |               |
        |               |                        |               |
        |      NS       |                        |               |
       8|-------------->|                        |               |
        |               |  Relay the Neighbor    |               |
        |               |     Solicit (NS)       |               |
        |              9|-----to CP via Si------>|               |
        |               |                        |   Accounting  |
        |               |                      10|<------------->|
        |               |  Send a Neighbor       |               |
        |               |     Advertise (NA)     |               |
        |             11|<----to UP via Si-------|               |
        |      NA       |                        |               |
      12|<--------------|                        |               |
        |               |                        |               |

                        Figure 16: IPv6 SLAAC Access

   It starts with a Router Solicit (RS) request from an RG that is
   tunneled to the CP by the UP.  After the AAA authentication and
   authorization, the CP will create a subscriber session on the UP.

   This is achieved by sending an Update_Request message to the UP (step
   4).

   The format of the Update_Request message is as follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   The UP will reply with an Update_Response message (step 5).  The
   format of the Update_Response message is as follows:

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.1.4.  DHCPv6 and SLAAC Access

   The following call flow (Figure 17) shows the DHCP IPv6 and SLAAC
   access process.

        RG              UP                       CP             AAA
        |      RS       |                        |               |
       1|-------------->|                        |               |
        |               |  Relay the RS          |               |
        |              2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                       3|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              4|<--------via Ci---------|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              5|---------via Ci-------->|               |
        |               |                        |               |
        |               |  Send RA               |               |
        |              6|<----to UP via Si-------|               |
        |      RA       |                        |               |
       7|<--------------|                        |               |
        |               |                        |               |
        |DHCPv6 Solicit |                        |               |
       8|-------------->|                        |               |
        |               |  Relay DHCPv6 Solicit  |               |
        |              9|-----to CP via Si------>|               |
        |               |                        |               |
        |               |  Update Subscriber     |               |
        |               |   Session Request      |               |
        |             10|<--------via Ci---------|               |
        |               |                        |               |
        |               |  Update Subscriber     |               |
        |               |   Session Response     |               |
        |             11|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      12|<------------->|
        |               |  Send DHCPv6 Reply     |               |
        |             13|<----to UP via Si-------|               |
        |               |                        |               |
        | DHCPv6 Reply  |                        |               |
      14|<--------------|                        |               |
        |               |                        |               |

                     Figure 17: DHCPv6 and SLAAC Access

   When a subscriber passes AAA authentication, the CP will create a
   subscriber session on the UP.  This is achieved by sending an
   Update_Request message to the UP (step 4).

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   The UP will reply with an Update_Response message (step 5).  The
   format of the Update_Response is as follows:

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   After receiving a DHCPv6 Solicit, the CP will update the subscriber
   session by sending an Update_Request message with new parameters to
   the UP (step 10).

   The format of the Update_Request message is as follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   The UP will reply with an Update_Response message (step 11).  The
   format of the Update_Response is as follows:

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.1.5.  DHCP Dual-Stack Access

   The following sequence (Figure 18) is a combination of DHCP IPv4 and
   DHCP IPv6 access processes.

        RG              UP                       CP             AAA
        | DHCP Discovery|                        |               |
       1|-------------->|                        |               |
        |               |Relay the DHCP Discovery|               |
        |              2|-----to CP via Si------>|     AAA       |
        |               |                        |   Req/Resp    |
        |               |                       3|<------------->|
        |               |  Send the DHCP Offer   |               |
        |              4|<----to UP via Si-------|               |
        |  DHCP Offer   |                        |               |
       5|<--------------|                        |               |
        |  DHCP Request |                        |               |
       6|-------------->|                        |               |
        |               |  Relay the DHCP Request|               |
        |              7|-----to CP via Si------>|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              8|<--------via Ci-------->|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              9|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      10|<------------->|
        |               |  Send DHCP ACK         |               |
        |             11|<----to UP via Si-------|               |
        |  DHCP ACK     |                        |               |
      12|<--------------|                        |               |
        |      RS       |                        |               |
      13|-------------->|                        |               |
        |               |  Relay the RS          |               |
        |             14|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                      15|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |             16|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |             17|---------via Ci-------->|               |
        |               |                        |               |
        |               |  Send the RA           |               |
        |             18|<----to UP via Si-------|               |
        |      RA       |                        |               |
      19|<--------------|                        |               |
        |DHCPv6 Solicit |                        |               |
      20|-------------->|                        |               |
        |               |  Relay DHCPv6 Solicit  |               |
        |             21|-----to CP via Si------>|               |
        |               |                        |               |
        |               |  Update Subscriber     |               |
        |               |   Session Request      |               |
        |             22|<--------via Ci---------|               |
        |               |  Update Subscriber     |               |
        |               |   Session Response     |               |
        |             23|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      24|<------------->|
        |               |  Send DHCPv6 Reply     |               |
        |             25|<----to UP via Si-------|               |
        | DHCPv6 Reply  |                        |               |
      26|<--------------|                        |               |
        |               |                        |               |

                     Figure 18: DHCP Dual-Stack Access

   The DHCP dual-stack access includes three sets of Update_Request/
   Update_Response exchanges to create/update a DHCPv4/v6 subscriber
   session.

   (1)  Create a DHCPv4 session (steps 8 and 9):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <IPv4 Subscriber TLV>
                        <IPv4 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>
                       [<Subscriber CGN Port Range TLV>]

   (2)  Create a DHCPv6 session (steps 16 and 17):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <IPv6 Subscriber TLV>
                        <IPv6 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>

   (3)  Update DHCPv6 session (steps 22 and 23):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <IPv6 Subscriber TLV>
                        <IPv6 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>

5.1.6.  L2 Static Subscriber Access

   L2 static subscriber access processes are as follows:

        RG              UP                      CP              AAA
        |               |    Static Subscriber   |               |
        |               |     Detection Req.     |               |
        |              1|<-----to UP via Ci------|               |
        |               |    Static Subscriber   |               |
        |               |     Detection Rep.     |               |
        |              2|------to UP via Ci----->|               |
        |  ARP/ND(REQ)  |                        |               |
     3.1|<--------------|                        |               |
        |  ARP/ND(ACK)  |                        |               |
     3.2|-------------->|                        |               |
        |               |  Relay the ARP/ND      |               |
        |            3.3|-----to CP via Si------>|       AAA     |
        |               |                        |    Req/Rep    |
        |               |                     3.4|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |            3.5|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |            3.6|---------via Ci-------->|               |
        |  ARP/ND(REQ)  |                        |               |
     4.1|-------------->|                        |               |
        |               |  Relay the ARP/ND      |               |
        |            4.2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                     4.3|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |            4.4|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |            4.5|---------via Ci-------->|               |
        |  ARP/ND(ACK)  |                        |               |
     4.6|<--------------|                        |               |
        |   IP Traffic  |                        |               |
     5.1|-------------->|                        |               |
        |               |  Relay the IP Traffic  |               |
        |            5.2|-----to CP via Si------>|      AAA      |
        |               |                        |    Req/Rep    |
        |               |                     5.3|<------------->|
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |            5.4|<--------via Ci-------->|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |            5.5|---------via Ci-------->|               |
        |  ARP/ND(REQ)  |                        |               |
     5.6|<--------------|                        |               |
        |  ARP/ND(ACK)  |                        |               |
     5.7|-------------->|                        |               |
        |               |                        |               |

                   Figure 19: L2 Static Subscriber Access

   For L2 static subscriber access, the process starts with a CP
   installing a static subscriber detection list on a UP.  The list
   determines which subscribers will be detected.  That is implemented
   by exchanging Update_Request and Update_Response messages between CP
   and UP.  The formats of the messages are as follows:

   <Update_Request Message> ::= <Common Header>
                     <IPv4 Static Subscriber Detect TLVs>
                     <IPv6 Static Subscriber Detect TLVs>

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   For L2 static subscriber access, there are three ways to trigger the
   access process:

   (1)  Triggered by UP (steps 3.1-3.6): This assumes that the UP knows
        the IP address, the access interface, and the VLAN of the RG.
        The UP will actively trigger the access flow by sending an ARP/
        ND packet to the RG.  If the RG is online, it will reply with an
        ARP/ND to the UP.  The UP will tunnel the ARP/ND to the CP
        through the Si.  The CP then triggers the authentication
        process.  If the authentication result is positive, the CP will
        create a corresponding subscriber session on the UP.

   (2)  Triggered by RG ARP/ND (steps 4.1-4.6): Most of the process is
        the same as option 1 (triggered by UP).  The difference is that
        the RG will actively send the ARP/ND to trigger the process.

   (3)  Triggered by RG IP traffic (steps 5.1-5.7): This is for the case
        where the RG has the ARP/ND information, but the subscriber
        session on the UP is lost (e.g., due to failure on the UP or the
        UP restarting).  That means the RG may keep sending IP packets
        to the UP.  The packets will trigger the UP to start a new
        access process.

   From a subscriber session point of view, the procedures and the
   message formats for the three cases above are the same, as follows.

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.2.  PPPoE

5.2.1.  IPv4 PPPoE Access

   Figure 20 shows the IPv4 PPPoE access call flow.

        RG              UP                      CP              AAA
        |  PPPoE Disc   |        PPPoE Disc      |               |
       1|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |  PPP LCP      |        PPP LCP         |               |
       2|<------------->|<---------via Si------->|               |
        |               |                        |      AAA      |
        |  PPP PAP/CHAP |        PPP PAP/CHAP    |    Req/Rep    |
       3|<------------->|<---------via Si------->|<------------->|
        |               |                        |               |
        |  PPP IPCP     |        PPP IPCP        |               |
       4|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              5|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              6|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                       7|<------------->|
        |               |                        |               |

                        Figure 20: IPv4 PPPoE Access

   In the above sequence, steps 1-4 are the standard PPPoE call flow.
   The UP is responsible for redirecting the PPPoE control packets to
   the CP or RG.  The PPPoE control packets are transmitted between the
   CP and UP through the Si.

   After the PPPoE call flow, if the subscriber passed the AAA
   authentication and authorization, the CP will create a corresponding
   session on the UP through the Ci.  The formats of the messages are as
   follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

5.2.2.  IPv6 PPPoE Access

   Figure 21 describes the IPv6 PPPoE access call flow.

        RG              UP                      CP              AAA
        |  PPPoE Disc   |        PPPoE Disc      |               |
       1|<------------->|<--------via Si-------->|               |
        |               |                        |               |
        |  PPP LCP      |        PPP LCP         |               |
       2|<------------->|<---------via Si------->|               |
        |               |                        |      AAA      |
        |  PPP PAP/CHAP |        PPP PAP/CHAP    |    Req/Rep    |
       3|<------------->|<---------via Si------->|<------------->|
        |               |                        |               |
        |  PPP IP6CP    |        PPP IP6CP       |               |
       4|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Create Subscriber     |               |
        |               |   Session Request      |               |
        |              5|<--------via Ci---------|               |
        |               |  Create Subscriber     |               |
        |               |   Session Response     |               |
        |              6|---------via Ci-------->|               |
        |               |                        |               |
        | ND Negotiation|        ND Negotiation  |               |
       7|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Update Subscriber     |               |
        |               |   Session Request      |               |
        |              8|<--------via Ci---------|               |
        |               |  Update Subscriber     |               |
        |               |   Session Response     |               |
        |              9|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      10|<------------->|
        |    DHCPv6     |        DHCPv6          |               |
        |  Negotiation  |      Negotiation       |               |
      7'|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Update Subscriber     |               |
        |               |   Session Request      |               |
        |             8'|<---------via Ci--------|               |
        |               |  Update Subscriber     |               |
        |               |   Session Response     |               |
        |             9'|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                     10'|<------------->|
        |               |                        |               |

                        Figure 21: IPv6 PPPoE Access

   From the above sequence, steps 1-4 are the standard PPPoE call flow.
   The UP is responsible for redirecting the PPPoE control packets to
   the CP or RG.  The PPPoE control packets are transmitted between the
   CP and UP through the Si.

   After the PPPoE call flow, if the subscriber passed the AAA
   authentication and authorization, the CP will create a corresponding
   session on the UP through the Ci.  The formats of the messages are as
   follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   Then, the RG will initialize an ND/DHCPv6 negotiation process with
   the CP (see steps 7 and 7'); after that, it will trigger an update
   (steps 8-9 and 8'-9') to the subscriber session.  The formats of the
   update messages are as follows:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.2.3.  PPPoE Dual-Stack Access

   Figure 22 shows a combination of IPv4 and IPv6 PPPoE access call
   flows.

        RG              UP                      CP              AAA
        |PPPoE Discovery|      PPPoE Discovery   |               |
       1|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |  PPP LCP      |        PPP LCP         |               |
       2|<------------->|<---------via Si------->|               |
        |               |                        |      AAA      |
        |  PPP PAP/CHAP |        PPP PAP/CHAP    |    Req/Rep    |
       3|<------------->|<---------via Si------->|<------------->|
        |               |                        |               |
        |  PPP IPCP     |        PPP IPCP        |               |
       4|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Create v4 Subscriber  |               |
        |               |   Session Request      |               |
        |              5|<--------via Ci---------|               |
        |               |  Create v4 Subscriber  |               |
        |               |   Session Response     |               |
        |              6|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                       7|<------------->|
        |  PPP IP6CP    |        PPP IP6CP       |               |
      4'|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Create V6 Subscriber  |               |
        |               |   Session Request      |               |
        |             5'|<--------via Ci---------|               |
        |               |  Create v6 Subscriber  |               |
        |               |   Session Response     |               |
        |             6'|---------via Ci-------->|               |
        |               |                        |               |
        | ND Negotiation|     ND Negotiation     |               |
       8|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Update v6 Subscriber  |               |
        |               |   Session Request      |               |
        |              9|<---------via Ci--------|               |
        |               |  Update v6 Subscriber  |               |
        |               |   Session Response     |               |
        |             10|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      7'|<------------->|
        |    DHCPv6     |        DHCPv6          |               |
        |  Negotiation  |      Negotiation       |               |
      8'|<------------->|<---------via Si------->|               |
        |               |                        |               |
        |               |  Update v6 Subscriber  |               |
        |               |   Session Request      |               |
        |             9'|<--------via Ci---------|               |
        |               |  Update v6 Subscriber  |               |
        |               |   Session Response     |               |
        |            10'|---------via Ci-------->|               |
        |               |                        |   Accounting  |
        |               |                      7"|<------------->|
        |               |                        |               |

                     Figure 22: PPPoE Dual-Stack Access

   PPPoE dual stack is a combination of IPv4 PPPoE and IPv6 PPPoE
   access.  The process is as above.  The formats of the messages are as
   follows:

   (1)  Create an IPv4 PPPoE subscriber session (steps 5-6):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <PPP Subscriber TLV>
                        <IPv4 Subscriber TLV>
                        <IPv4 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>
                       [<Subscriber CGN Port Range TLV>]

   (2)  Create an IPv6 PPPoE subscriber session (steps 5'-6'):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <PPP Subscriber TLV>
                        <IPv6 Subscriber TLV>
                        <IPv6 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>

   (3)  Update the IPv6 PPPoE subscriber session (steps 9-10 and 9'-
        10'):

      <Update_Request Message> ::= <Common Header>
                        <Basic Subscriber TLV>
                        <PPP Subscriber TLV>
                        <IPv6 Subscriber TLV>
                        <IPv6 Routing TLV>
                        [<Subscriber Policy TLV>]

      <Update_Response Message> ::= <Common Header>
                       <Update Response TLV>

5.3.  WLAN Access

   Figure 23 shows the WLAN access call flow.

        RG            UP              CP         AAA      Web Server
        |    DHCP     |                |          |           |
        |  Discovery  |                |          |           |
       1|------------>|                |          |           |
        |             | DHCP Discovery |          |           |
        |            2|-----via Si---->|   AAA    |           |
        |             |   DHCP Offer   |<-------->|           |
        |            3|<----via Si-----|          |           |
        |  DHCP Offer |                |          |           |
       4|<------------|                |          |           |
        | DHCP Request|                |          |           |
       5|------------>|                |          |           |
        |             |  DHCP Request  |          |           |
        |            6|-----via Si---->|          |           |
        |             |                |          |           |
        |             | Create Session |          |           |
        |             |    Request     |          |           |
        |            7|<----via Ci-----|          |           |
        |             | Create Session |          |           |
        |             |    Response    |          |           |
        |            8|----via Ci----->|          |           |
        |             |                |          |           |
        |             |  DHCP ACK      |          |           |
        |            9|<----via Si-----|          |           |
        |  DHCP ACK   |                |          |           |
      10|<------------|                |          |           |
        |             |                |          |           |
        | Subscriber  |                |          |           |
        | HTTP Traffic|                |          |           |
      11|------------>|-->             |          |           |
        |             |  | Web URL     |          |           |
        |  Traffic    |  | Redirect    |          |           |
        | Redirection |  |             |          |           |
      12|<------------|<-+             |          |           |
        |                                                     |
      13|-----------------Redirect to Web Server------------->|
        |                                                     |
      14|<----------------Push HTTP Log-in Page---------------|
        |                                                     |
      15|-----------------User Authentication---------------->|
        |                                                     |
        |             |                |  Portal Interchange  |
        |             |              16|<-------------------->|
        |             |                |                      |
        |             |                |   AAA    |           |
        |             |                |  Req/Rep |           |
        |             |              17|<-------->|           |
        |             |                |          |           |
        |             | Update Session |          |           |
        |             |    Request     |          |           |
        |           18|<----via Ci-----|          |           |
        |             | Update Session |          |           |
        |             |    Response    |          |           |
        |           19|-----via Ci---->|          |           |
        |             |                |          |           |

                           Figure 23: WLAN Access

   WLAN access starts with the DHCP dial-up process (steps 1-6).  After
   that, the CP will create a subscriber session on the UP (steps 7-8).
   The formats of the session creation messages are as follows:

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   After step 10, the RG will be allocated an IP address, and its first
   HTTP packet will be redirected to a web server for subscriber
   authentication (steps 11-17).  After the web authentication, if the
   result is positive, the CP will update the subscriber session by
   using the following message exchanges:

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.4.  L2TP

5.4.1.  L2TP LAC Access

        RG         UP(LAC)      CP(LAC)     AAA        LNS
        |    PPPoE   |    PPPoE     |        |          |
        |  Discovery |   Discovery  |        |          |
       1|<---------->|<---via Si--->|        |          |
        |            |              |        |          |
        |  PPP LCP   |   PPP LCP    |        |          |
       2|<---------->|<---via Si--->|        |          |
        |            |              |   AAA  |          |
        |PPP PAP/CHAP| PPP PAP/CHAP | Req/Rep|          |
       3|<---------->|<---via Si--->|<------>|          |
        |            |              |        |          |
        |  PPP IPCP  |  PPP IPCP    |        |          |
       4|<---------->|<---via Si--->|        |          |
        |            |              |        |          |
        |            | L2TP Tunnel  |        |          |
        |            | Negotiation  |        |          |
        |            |   SCCRQ/     |        |          |
        |            |   SCCRP/     |        |          |
        |            |   SCCCN      |        |          |
        |           5|<---via Si--->|        |          |
        |            | /\                               |
        |            | || Forward                       |
        |            | \/                               |
        |            |<-----------via Routing---------->|
        |            |                                  |
        |            | L2TP Session |        |          |
        |            | Negotiation  |        |          |
        |            |    ICRQ/     |        |          |
        |            |    ICRP/     |        |          |
        |            |    ICCN      |        |          |
        |           6|<---via Si--->|        |          |
        |            | /\                               |
        |            | || Forward                       |
        |            | \/                               |
        |            |<-----------via Routing---------->|
        |            |                                  |
        |            |    Create    |         |         |
        |            |  Subscriber  |         |         |
        |            |  Session Req |         |         |
        |           7|<---via Ci----|         |         |
        |            |    Create    |         |         |
        |            |  Subscriber  |         |         |
        |            |  Session Rep |         |         |
        |           8|----via Ci--->|         |         |
        |            |              |         |         |
        |                                               |
        |         PAP/CHAP (Triggered by LNS)           |
       9|<-----------------via Routing----------------->|
        |                                               |

                         Figure 24: L2TP LAC Access

   Steps 1-4 are a standard PPPoE access process.  After that, the LAC-
   CP starts to negotiate an L2TP session and tunnel with the LNS.
   After the negotiation, the CP will create an L2TP LAC subscriber
   session on the UP through the following messages:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <L2TP-LAC Subscriber TLV>
                     <L2TP-LAC Tunnel TLV>

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.4.2.  L2TP LNS IPv4 Access

        RG          LAC            UP(LNS)  AAA      CP(LNS)
        |    PPPoE   |              |        |          |
        |  Discovery |              |        |          |
       1|<---------->|              |        |          |
        |            |              |        |          |
        |  PPP LCP   |              |        |          |
       2|<---------->|                       |          |
        |            |          AAA          |          |
        |PPP PAP/CHAP|        Req/Rep        |          |
       3|<---------->|<--------------------->|          |
        |            |                                  |
        |            | L2TP Tunnel  |     L2TP Tunnel   |
        |            | Negotiation  |     Negotiation   |
        |            |   SCCRQ/     |       SCCRQ/      |
        |            |   SCCRP/     |       SCCRP/      |
        |            |   SCCCN      |       SCCCN       |
        |           4|<------------>|<------via Si----->|
        |            |              |                   |
        |            | L2TP Session |     L2TP Session  |
        |            | Negotiation  |     Negotiation   |
        |            |    ICRQ/     |        ICRQ/      |
        |            |    ICRP/     |        ICRP/      |
        |            |    ICCN      |        ICCN       |
        |           5|<------------>|<------via Si----->|
        |            |              |                   |
        |            |              | Create Subscriber |
        |            |              | Session Request   |
        |            |             6|<-----via Ci-------|
        |            |              | Create Subscriber |
        |            |              | Session Response  |
        |            |             7|------via Ci------>|
        |                                               |
        |          PAP/CHAP (Triggered by LNS)          |
       8|<--------------------------------------------->|
        |                                               |
        |            |              |        |    AAA   |
        |            |              |        |  Req/Rep |
        |            |              |       9|<-------->|
        |            |              |                   |
        |                                               |
        |                   PPP IPCP                    |
      10|<--------------------------------------------->|
        |                                               |
        |            |              | Update Subscriber |
        |            |              | Session Request   |
        |            |            11|<-----via Ci-------|
        |            |              | Update Subscriber |
        |            |              | Session Response  |
        |            |            12|------via Ci------>|
        |            |              |                   |

                      Figure 25: L2TP LNS IPv4 Access

   In this case, the BNG is running as an LNS and separated into LNS-CP
   and LNS-UP.  Steps 1-5 finish the normal L2TP dial-up process.  When
   the L2TP session and tunnel negotiations are finished, the LNS-CP
   will create an L2TP LNS subscriber session on the LNS-UP.  The format
   of the messages is as follows:

   <Update_Request Message> ::= <Common Header>
                     <L2TP-LNS Subscriber TLV>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     <L2TP-LNS Tunnel TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   After that, the LNS-CP will trigger a AAA authentication.  If the
   authentication result is positive, a PPP IP Control Protocol (IPCP)
   process will follow, and then the CP will update the session with the
   following message exchanges:

   <Update_Request Message> ::= <Common Header>
                     <L2TP-LNS Subscriber TLV>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     <L2TP-LNS Tunnel TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

5.4.3.  L2TP LNS IPv6 Access

        RG          LAC          UP(LNS)    AAA      CP(LNS)
        |    PPPoE   |              |        |          |
        |  Discovery |              |        |          |
       1|<---------->|              |        |          |
        |            |              |        |          |
        |  PPP LCP   |              |        |          |
       2|<---------->|                       |          |
        |            |          AAA          |          |
        |PPP PAP/CHAP|        Req/Rep        |          |
       3|<---------->|<--------------------->|          |
        |            |                                  |
        |            | L2TP Tunnel  |     L2TP Tunnel   |
        |            | Negotiation  |     Negotiation   |
        |            |   SCCRQ/     |       SCCRQ/      |
        |            |   SCCRP/     |       SCCRP/      |
        |            |   SCCCN      |       SCCCN       |
        |           4|<------------>|<------via Si----->|
        |            |              |                   |
        |            | L2TP Session |     L2TP Session  |
        |            | Negotiation  |     Negotiation   |
        |            |    ICRQ/     |        ICRQ/      |
        |            |    ICRP/     |        ICRP/      |
        |            |    ICCN      |        ICCN       |
        |           5|<------------>|<------via Si----->|
        |            |              |                   |
        |            |              | Create Subscriber |
        |            |              | Session Request   |
        |            |             6|<-----via Ci-------|
        |            |              | Create Subscriber |
        |            |              | Session Response  |
        |            |             7|------via Ci------>|
        |                                               |
        |          PAP/CHAP (Triggered by LNS)          |
       8|<--------------------------------------------->|
        |                                               |
        |            |              |        |    AAA   |
        |            |              |        |  Req/Rep |
        |            |              |       9|<-------->|
        |            |              |        |          |
        |                                               |
        |                   PPP IP6CP                   |
      10|<--------------------------------------------->|
        |                                               |
        |            |              | Update Subscriber |
        |            |              | Session Request   |
        |            |            11|<-----via Ci-------|
        |            |              | Update Subscriber |
        |            |              | Session Response  |
        |            |            12|------via Ci------>|
        |                           |                   |
        |       ND Negotiation      |   ND Negotiation  |
      13|<------------------------->|<-----via Si------>|
        |                           |                   |
        |            |              | Update Subscriber |
        |            |              | Session Request   |
        |            |            14|<-----via Ci-------|
        |            |              | Update Subscriber |
        |            |              | Session Response  |
        |            |            15|------via Ci------>|
        |            |              |                   |

                      Figure 26: L2TP LNS IPv6 Access

   Steps 1-12 are the same as L2TP LNS IPv4 access.  Steps 1-5 finish
   the normal L2TP dial-up process.  When the L2TP session and tunnel
   negotiations are finished, the LNS-CP will create an L2TP LNS
   subscriber session on the LNS-UP.  The format of the messages is as
   follows:

   <Update_Request Message> ::= <Common Header>
                     <L2TP-LNS Subscriber TLV>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     <L2TP-LNS Tunnel TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   After that, the LNS-CP will trigger a AAA authentication.  If the
   authentication result is positive, a PPP IP6CP process will follow,
   and then the CP will update the session with the following message
   exchanges:

   <Update_Request Message> ::= <Common Header>
                     <L2TP-LNS Subscriber TLV>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     <L2TP-LNS Tunnel TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   Then, an ND negotiation will be triggered by the RG.  After the ND
   negotiation, the CP will update the session with the following
   message exchanges:

   <Update_Request Message> ::= <Common Header>
                     <L2TP-LAC Subscriber TLV>
                     <Basic Subscriber TLV>
                     <PPP Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     <L2TP-LNS Tunnel TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.5.  CGN (Carrier Grade NAT)

          RG              UP                       CP             AAA
          |               |  Public Address Block  |               |
          |               |   Allocation Request   |               |
          |              1|<--------via Ci-------->|               |
          |               |  Public Address Block  |               |
          |               |   Allocation Reply     |               |
          |              2|---------via Ci-------->|               |
          |   Subscriber  |                        |               |
          | Access Request|        Subscriber      |               |
         3|-------------->|      Access Request    |               |
          |              4|----------via Si------->|               |
          |               |                        |      AAA      |
          |               |       Subscriber       |    Req/Rep    |
          |  Subscriber   |      Access Reply     5|<------------->|
          | Access Reply 6|<---------via Si--------|               |
         7|<--------------|                        |               |
          |               |  Create Subscriber     |               |
          |               |   Session Request      |               |
          |              8|<--------via Ci---------|               |
          |               |                        |               |
          |               |  Create Subscriber     |               |
          |               |   Session Response     |               |
          |               | (with NAT information) |               |
          |              9|---------via Ci-------->|               |
          |               |                        |   Accounting  |
          |               |                        |  with source  |
          |               |                        |   information |
          |               |                      10|<------------->|
          |               |                        |  Public IP +  |
          |               |                        |  Port Range   |
          |               |                        |  to Private IP|
          |               |                        |  Mapping      |
          |               |                        |               |

                           Figure 27: CGN Access

   The first steps allocate one or more CGN address blocks to the UP
   (steps 1-2).  This is achieved by the following message exchanges
   between CP and UP:

   <Addr_Allocation_Req Message> ::= <Common Header>
                     <Address Allocation Request TLV>

   <Addr_Allocation_Ack Message> ::= <Common Header>
                    <Address Allocation Response TLV>

   Steps 3-9 show the general dial-up process in the case of CGN mode.
   The specific processes (e.g., IPoE, PPPoE, L2TP, etc.) are defined in
   above sections.

   If a subscriber is a CGN subscriber, once the subscriber session is
   created/updated, the UP will report the NAT information to the CP.
   This is achieved by carrying the Subscriber CGN Port Range TLV in the
   Update_Response message.

5.6.  L3 Leased Line Access

5.6.1.  Web Authentication

        RG            UP              CP         AAA      Web Server
        | User traffic|                |          |           |
       1|------------>|                |          |           |
        |             | User traffic   |          |           |
        |            2|-----via Si---->|    AAA   |           |
        |             |                |  Req/Rep |           |
        |             |               3|<-------->|           |
        |             | Create Session |          |           |
        |             |    Request     |          |           |
        |            4|<----via Ci-----|          |           |
        |             | Create Session |          |           |
        |             |    Response    |          |           |
        |            5|----via Ci----->|          |           |
        |             |                |          |           |
        | HTTP traffic|                |          |           |
       6|------------>|                |          |           |
        |             |                |          |           |
        | Redirect to |                |          |           |
        |   Web URL   |                |          |           |
       7|<------------|                |          |           |
        |             |                |          |           |
        |                                                     |
       8|-----------------Redirected to Web Server----------->|
        |                                                     |
       9|<----------------Push HTTP Log-in Page---------------|
        |                                                     |
      10|-----------------User Authentication---------------->|
        |                                                     |
        |             |                |  Portal Interchange  |
        |             |              11|<-------------------->|
        |             |                |                      |
        |             |                |   AAA    |           |
        |             |                |  Req/Rep |           |
        |             |              12|<-------->|           |
        |             |                |          |           |
        |             | Update Session |          |           |
        |             |    Request     |          |           |
        |           13|<----via Ci-----|          |           |
        |             | Update Session |          |           |
        |             |    Response    |          |           |
        |           14|----via Ci----->|          |           |
        |             |                |          |           |

         Figure 28: Web Authentication-Based L3 Leased Line Access

   In this case, IP traffic from the RG will trigger the CP to
   authenticate the RG by checking the source IP and the exchanges with
   the AAA server.  Once the RG has passed the authentication, the CP
   will create a corresponding subscriber session on the UP through the
   following message exchanges:

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>

                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

   Then, the HTTP traffic from the RG will be redirected to a web server
   to finish the web authentication.  Once the web authentication is
   passed, the CP will trigger another AAA authentication.  After the
   AAA authentication, the CP will update the session with the following
   message exchanges:

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.6.2.  User Traffic Trigger

        RG            UP              CP         AAA
        |             |   L3 access    |          |
        |             |  control list  |          |
        |            1|<----via Ci-----|          |
        |    User     |                |          |
        |   traffic   |                |          |
       2|------------>|                |          |
        |             |  User traffic  |          |
        |            3|-----via Si---->|          |
        |             |                |   AAA    |
        |             |                |  Req/Rep |
        |             |               4|<-------->|
        |             |                |          |
        |             | Create Session |          |
        |             |    Request     |          |
        |            5|<----via Ci-----|          |
        |             | Create Session |          |
        |             |    Response    |          |
        |            6|----via Ci----->|          |
        |             |                |          |

          Figure 29: User Traffic Triggered L3 Leased Line Access

   In this case, the CP must install on the UP an access control list,
   which is used by the UP to determine whether or not an RG is legal.
   If the traffic is from a legal RG, it will be redirected to the CP
   though the Si.  The CP will trigger a AAA interchange with the AAA
   server.  After that, the CP will create a corresponding subscriber
   session on the UP with the following message exchanges:

   IPv4 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv4 Subscriber TLV>
                     <IPv4 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>
                    [<Subscriber CGN Port Range TLV>]

   IPv6 Case:

   <Update_Request Message> ::= <Common Header>
                     <Basic Subscriber TLV>
                     <IPv6 Subscriber TLV>
                     <IPv6 Routing TLV>
                     [<Subscriber Policy TLV>]

   <Update_Response Message> ::= <Common Header>
                    <Update Response TLV>

5.7.  Multicast Service Access

              RG            UP              CP         AAA
              | User Access |  User Access   |   AAA    |
              |   Request   |    Request     |  Req/Rep |
             1|<----------->|<----via Si---->|<-------->|
              |             |                |          |
              |             | Create Session |          |
              |             |    Request     |          |
              |            2|<----via Ci---->|          |
              |             |                |          |
              |             | Create Session |          |
              |             |    Response    |          |
              |            3|----via Ci----->|          |
              |             |                |          |
              |  Multicast  |                |          |
              | negotiation |                |          |
             4|<----------->|                |          |
              |             |                |          |

                        Figure 30: Multicast Access

   Multicast access starts with a user access request from the RG.  The
   request will be redirected to the CP by the Si.  A follow-up AAA
   interchange between the CP and the AAA server will be triggered.
   After the authentication, the CP will create a multicast subscriber
   session on the UP through the following messages:

   IPv4 Case, there will be a Multicast-ProfileV4 sub-TLV present in the
   Subscriber Policy TLV:

   <Update_Request Message> ::= <Common Header>
                  <Basic Subscriber TLV>
                  <IPv4 Subscriber TLV>
                  <IPv4 Routing TLV>
                  <Subscriber Policy TLV>

   <Update_Response Message> ::= <Common Header>
                 <Update Response TLV>
                 [<Subscriber CGN Port Range TLV>]

   IPv6 Case, there will be a Multicast-ProfileV6 sub-TLV present in the
   Subscriber Policy TLV:

   <Update_Request Message> ::= <Common Header>
                  <Basic Subscriber TLV>
                  <IPv6 Subscriber TLV>
                  <IPv6 Routing TLV>
                  <Subscriber Policy TLV>

   <Update_Response Message> ::= <Common Header>
                 <Update Response TLV>

6.  S-CUSP Message Formats

   An S-CUSP message consists of a common header followed by a variable-
   length body consisting entirely of TLVs.  Receiving an S-CUSP message
   with an unknown message type or missing mandatory TLV MUST trigger an
   Error message (see Section 6.7) or a Response message with an Error
   Information TLV (see Section 7.6).

   Conversely, if a TLV is optional, the TLV may or may not be present.
   Optional TLVs are indicated in the message formats shown in this
   document by being enclosed in square brackets.

   This section specifies the format of the common S-CUSP message header
   and lists the defined messages.

   Network byte order is used for all multi-byte fields.

6.1.  Common Message Header

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Ver  |  Resv | Message-Type  |        Message-Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Reserved           |        Transaction-ID         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 31: S-CUSP Message Common Header

   Ver (4 bits):  The major version of the protocol.  This document
      specifies version 1.  Different major versions of the protocol may
      have significantly different message structures and formats except
      that the Ver field will always be in the same place at the
      beginning of each message.  A successful S-CUSP session depends on
      the CP and the UP both using the same major version of the
      protocol.

   Resv (4 bits):  Reserved.  MUST be sent as zero and ignored on
      receipt.

   Message-Type (8 bits):  The set of message types specified in this
      document is listed in Section 8.1.

   Message-Length (16 bits):  Total length of the S-CUSP message
      including the common header, expressed in number of bytes as an
      unsigned integer.

   Transaction-ID (16 bits):  This field is used to identify requests.
      It is echoed back in any corresponding ACK/Response/Error message.
      It is RECOMMENDED that a monotonically increasing value be used in
      successive messages and that the value wraps back to zero after
      0xFFFF.  The content of this field is an opaque value that the
      receiver MUST NOT use for any purpose except to echo back in a
      corresponding response and, optionally, for logging.

6.2.  Control Messages

   This document defines the following control messages:

      +------+-----------------+------------------------------------+
      | Type | Name            | Notes and TLVs that can be carried |
      +======+=================+====================================+
      | 1    | Hello           | Hello TLV, Keepalive TLV           |
      +------+-----------------+------------------------------------+
      | 2    | Keepalive       | A common header with the Keepalive |
      |      |                 | message type                       |
      +------+-----------------+------------------------------------+
      | 3    | Sync_Request    | Synchronization request            |
      +------+-----------------+------------------------------------+
      | 4    | Sync_Begin      | Synchronization starts             |
      +------+-----------------+------------------------------------+
      | 5    | Sync_Data       | Synchronization data: TLVs         |
      |      |                 | specified in Section 7             |
      +------+-----------------+------------------------------------+
      | 6    | Sync_End        | End synchronization                |
      +------+-----------------+------------------------------------+
      | 7    | Update_Request  | TLVs specified in Sections 7.6-7.9 |
      +------+-----------------+------------------------------------+
      | 8    | Update_Response | TLVs specified in Sections 7.6-7.9 |
      +------+-----------------+------------------------------------+

                         Table 2: Control Messages

6.2.1.  Hello Message

   The Hello message is used for S-CUSP session establishment and
   version negotiation.  The details of S-CUSP session establishment and
   version negotiation can be found in Section 4.1.1.

   The format of the Hello message is as follows:

   <Hello Message> ::= <Common Header>
                        <Hello TLV>
                        <Keepalive TLV>
                        [<Error Information TLV>]

   The return code and negotiation result will be carried in the Error
   Information TLV.  They are listed as follows:

   0:  Success.  Version negotiation success.

   1:  Failure.  Malformed message received.

   2:  TLV-Unknown.  One or more of the TLVs was not understood.

   1001:  Version-Mismatch.  The version negotiation fails.  The S-CUSP
      session establishment phase fails.

   1002:  Keepalive Error.  The keepalive negotiation fails.  The S-CUSP
      session establishment phase fails.

   1003:  Timer Expires.  The establishment timer expired.  Session
      establishment phase fails.

6.2.2.  Keepalive Message

   Each end of an S-CUSP session periodically sends a Keepalive message.
   It is used to detect whether the peer end is still alive.  The
   Keepalive procedures are defined in Section 4.1.2.

   The format of the Keepalive message is as follows:

   <Keepalive Message> ::= <Common Header>

6.2.3.  Sync_Request Message

   The Sync_Request message is used to request synchronization from an
   S-CUSP peer.  Both CP and UP can request their peer to synchronize
   data.

   The format of the Sync_Request message is as follows:

   <Sync_Request Message> ::= <Common Header>

   A Sync_Request message may result in a Sync_Begin message from its
   peer.  The Sync_Begin message is defined in Section 6.2.4.

6.2.4.  Sync_Begin Message

   The Sync_Begin message is a reply to a Sync_Request message.  It is
   used to notify the synchronization requester whether the
   synchronization can be started.

   The format of the Sync_Begin message is as follows:

   <Sync_Begin Message> ::= <Common Header>
                           <Error Information TLV>

   The return codes are carried in the Error Information TLV.  The codes
   are listed below:

   0:  Success.  Be ready to synchronize.

   1:  Failure.  Malformed message received.

   2:  TLV-Unknown.  One or more of the TLVs was not understood.

   2001:  Synch-NoReady.  The data to be synchronized is not ready.

   2002:  Synch-Unsupport.  The data synchronization is not supported.

6.2.5.  Sync_Data Message

   The Sync_Data message is used to send data being synchronized between
   the CP and UP.  The Sync_Data message has the same function and
   format as the Update_Request message.  The difference is that there
   is no ACK for a Sync_Data message.  An error caused by the Sync_Data
   message will result in a Sync_End message.

   There are two scenarios:

   *  Synchronization from UP to CP: Synchronize the resource data to
      CP.

            <Sync_Data Message> ::= <Common Header>
                                    [<Interface Status TLV>]
                                    [<Board Status TLV>]

   *  Synchronization from CP to UP: Synchronize all subscriber sessions
      to the UP.  The Subscriber TLVs carried are those appearing in
      Section 7.9.  As for which TLVs should be carried, it depends on
      the specific session data to be synchronized.  The process is
      equivalent to the creation of a particular session.  Refer to
      Section 5 to see more details.

            <Sync_Data Message> ::= <Common Header>
                                 [<IPv4 Routing TLV>]
                                 [<IPv6 Routing TLV>]
                                 [<Subscriber TLVs>]

6.2.6.  Sync_End Message

   The Sync_End message is used to indicate the end of a synchronization
   process.  The format of a Sync_End message is as follows:

   <Sync_End Message> ::= <Common Header>
                           <Error Information TLV>

   The return/error codes are listed as follows:

   0:  Success.  Synchronization finished.

   1:  Failure.  Malformed message received.

   2:  TLV-Unknown.  One or more of the TLVs was not understood.

6.2.7.  Update_Request Message

   The Update_Request message is a multipurpose message; it can be used
   to create, update, and delete subscriber sessions on a UP.

   For session operations, the specific operation is controlled by the
   Oper field of the carried TLVs.  As defined in Section 7.1, the Oper
   field can be set to either Update or Delete when a TLV is carried in
   an Update_Request message.

   When the Oper field is set to Update, it means to create or update a
   subscriber session.  If the Oper field is set to Delete, it is a
   request to delete a corresponding session.

   The format of the Update_Request message is as follows:

   <Update_Request Message> ::= <Common Header>
                           [<IPv4 Routing TLV>]
                           [<IPv6 Routing TLV>]
                           [<Subscriber TLVs>]

   Where the Subscriber TLVs are those appearing in Section 7.9.  Each
   Update_Request message will result in an Update_Response message,
   which is defined in Section 6.2.8.

6.2.8.  Update_Response Message

   The Update_Response message is a response to an Update_Request
   message.  It is used to confirm the update request (or reject it in
   the case of an error).  The format of an Update_Response message is
   as follows:

   <Update_Response Message> ::= <Common Header>
                           [<Subscriber CGN Port Range TLV>]
                           <Error Information TLV>

   The return/error codes are carried in the Error Information TLV.
   They are listed as follows:

   0:  Success.

   1:  Failure.  Malformed message received.

   2:  TLV-Unknown.  One or more of the TLVs was not understood.

   3001:  Pool-Mismatch.  The corresponding address pool cannot be
      found.

   3002:  Pool-Full.  The address pool is fully allocated, and no
      address segment is available.

   3003:  Subnet-Mismatch.  The address pool subnet cannot be found.

   3004:  Subnet-Conflict.  Subnets in the address pool have been
      classified into other clients.

   4001:  Update-Fail-No-Res. The forwarding table fails to be delivered
      because the forwarding resources are insufficient.

   4002:  QoS-Update-Success.  The QoS policy takes effect.

   4003:  QoS-Update-Sq-Fail.  Failed to process the queue in the QoS
      policy.

   4004:  QoS-Update-CAR-Fail.  Processing of the CAR in the QoS policy
      fails.

   4005:  Statistic-Fail-No-Res. Statistics processing failed due to
      insufficient statistics resources.

6.3.  Event Message

   The Event message is used to report subscriber session traffic
   statistics and detection information.  The format of the Event
   message is as follows:

   <Event Message> ::= <Common Header>
                           [<Subscriber Traffic Statistics Report TLV>]
                           [<Subscriber Detection Result Report TLV>]

6.4.  Report Message

   The Report message is used to report board and interface status on a
   UP.  The format of the Report message is as follows:

   <Report Message> ::= <Common Header>
                           [<Board Status TLVs>]
                           [<Interface Status TLVs>]

6.5.  CGN Messages

   This document defines the following resource allocation messages:

       +------+---------------------+-----------------------------+
       | Type | Message Name        | TLV that is carried         |
       +======+=====================+=============================+
       | 200  | Addr_Allocation_Req | Address Allocation Request  |
       +------+---------------------+-----------------------------+
       | 201  | Addr_Allocation_Ack | Address Allocation Response |
       +------+---------------------+-----------------------------+
       | 202  | Addr_Renew_Req      | Address Renewal Request     |
       +------+---------------------+-----------------------------+
       | 203  | Addr_Renew_Ack      | Address Renewal Response    |
       +------+---------------------+-----------------------------+
       | 204  | Addr_Release_Req    | Address Release Request     |
       +------+---------------------+-----------------------------+
       | 205  | Addr_Release_Ack    | Address Release Response    |
       +------+---------------------+-----------------------------+

                  Table 3: Resource Allocation Messages

6.5.1.  Addr_Allocation_Req Message

   The Addr_Allocation_Req message is used to request CGN address
   allocation.  The format of the Addr_Allocation_Req message is as
   follows:

   <Addr_Allocation_Req Message> ::= <Common Header>
                           <Address Allocation Request TLV>

6.5.2.  Addr_Allocation_Ack Message

   The Addr_Allocation_Ack message is a response to an
   Addr_Allocation_Req message.  The format of the Addr_Allocation_Ack
   message is as follows:

   <Addr_Allocation_Ack Message> ::= <Common Header>
                           <Address Allocation Response TLV>

6.5.3.  Addr_Renew_Req Message

   The Addr_Renew_Req message is used to request address renewal.  The
   format of the Addr_Renew_Req message is as follows:

   <Addr_Renew_Req Message> ::= <Common Header>
                           <Address Renewal Request TLV>

6.5.4.  Addr_Renew_Ack Message

   The Addr_Renew_Ack message is a response to an Addr_Renew_Req
   message.  The format of the Addr_Renew_Req message is as follows:

   <Addr_Renew_Ack Message> ::= <Common Header>
                           <Address Renewal Response TLV>

6.5.5.  Addr_Release_Req Message

   The Addr_Release_Req message is used to request address release.  The
   format of the Addr_Release_Req message is as follows:

   <Addr_Release_Req Message> ::= <Common Header>
                           <Address Release Request TLV>

6.5.6.  Addr_Release_Ack Message

   The Addr_Release_Ack message is a response to an Addr_Release_Req
   message.  The format of the Addr_Release_Ack message is as follows:

   <Addr_Release_Ack Message> ::= <Common Header>
                           <Address Release Response TLV>

6.6.  Vendor Message

   The Vendor message, in conjunction with the Vendor TLV and Vendor
   sub-TLV, can be used by vendors to extend S-CUSP.  The Message-Type
   is 11.  If the receiver does not recognize the message, an Error
   message will be returned to the sender.

   The format of the Vendor message is as follows:

   <Vendor Message> ::= <Common Header>
                        <Vendor TLV>
                        [<any other TLVs as specified by the vendor>]

6.7.  Error Message

   The Error message is defined to return some critical error
   information to the sender.  If a receiver does not support the type
   of the received message, it MUST return an Error message to the
   sender.

   The format of the Error message is as below:

   <Error Message> ::= <Common Header>
                       <Error Information TLV>

7.  S-CUSP TLVs and Sub-TLVs

   This section specifies the following:

   *  The format of the TLVs that appear in S-CUSP messages,

   *  The format of the sub-TLVs that appear within the values of some
      TLVs, and

   *  The format of some basic data fields that appear within TLVs or
      sub-TLVs.

   See Section 8 for a list of all defined TLVs and sub-TLVs.

7.1.  Common TLV Header

   S-CUSP messages consist of the common header specified in Section 6.1
   followed by TLVs formatted as specified in this section.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Oper  |      TLV-Type         |       TLV-Length              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                             Value                             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 32: Common TLV Header

   Oper (4 bits):  For Message-Types that specify an operation on a data
      set, the Oper field is interpreted as Update, Delete, or Reserved
      as specified in Section 8.3.  For all other Message-Types, the
      Oper field MUST be sent as zero and ignored on receipt.

   TLV-Type (12 bits):  The type of a TLV.  TLV-Type specifies the
      interpretation and format of the Value field of the TLV.  See
      Section 8.2.

   TLV-Length (2 bytes):  The length of the Value portion of the TLV in
      bytes as an unsigned integer.

   Value (variable length):  This is the portion of the TLV whose size
      is given by TLV-Length.  It consists of fields, frequently using
      one of the basic data field types (see Section 7.2) and sub-TLVs
      (see Section 7.3).

7.2.  Basic Data Fields

   This section specifies the binary format of several standard basic
   data fields that are used within other data structures in this
   specification.

   STRING:  0 to 255 octets.  Will be encoded as a sub-TLV (see
      Section 7.3) to provide the length.  The use of this data type in
      S-CUSP is to provide convenient labels for use by network
      operators in configuring and debugging their networks and
      interpreting S-CUSP messages.  Subscribers will not normally see
      these labels.  They are normally interpreted as ASCII [RFC20].

   MAC-Addr:  6 octets.  Ethernet MAC address [RFC7042].

   IPv4-Address:  8 octets. 4 octets of the IPv4 address value followed
      by a 4-octet address mask in the format XXX.XXX.XXX.XXX.

   IPv6-Address:  20 octets. 16 octets of the IPv6 address followed by a
      4-octet integer n in the range of 0 to 128, which gives the
      address mask as the one's complement of 2**(128-n) - 1.

   VLAN ID:  2 octets.  As follows [802.1Q]:

             0                   1
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            | PRI |D|      VLAN-ID          |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      PRI:  Priority.  Default value 7.

      D:  Drop Eligibility Indicator (DEI).  Default value 0.

      VLAN-ID:  Unsigned integer in the range 1-4094. (0 and 4095 are
         not valid VLAN IDs [802.1Q].)

7.3.  Sub-TLV Format and Sub-TLVs

   In some cases, the Value portion of a TLV, as specified in
   Section 7.1, can contain one or more sub-TLVs formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Type             |          Length               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Value                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

                         Figure 33: Sub-TLV Header

   Type (2 bytes):  The type of a sub-TLV.  The Type field specifies the
      interpretation and format of the Value field of the TLV.  Sub-TLV
      type values have the same meaning regardless of the TLV type of
      the TLV within which the sub-TLV occurs.  See Section 8.4.

   Length (2 bytes):  The length of the Value portion of the sub-TLV in
      bytes as an unsigned integer.

   Value (variable length):  This is the Value portion of the sub-TLV
      whose size is given by Length.

   The sub-TLVs currently specified are defined in the following
   subsections.

7.3.1.  Name Sub-TLVs

   This document defines the following name sub-TLVs that are used to
   carry the name of the corresponding object.  The length of each of
   these sub-TLVs is variable from 1 to 255 octets.  The value is of
   type STRING padded with zero octets to a length in octets that is an
   integer multiple of 4.

    +------+---------------------+------------------------------------+
    | Type | Sub-TLV Name        | Meaning                            |
    +======+=====================+====================================+
    | 1    | VRF-Name            | The name of a VRF                  |
    +------+---------------------+------------------------------------+
    | 2    | Ingress-QoS-Profile | The name of an ingress QoS profile |
    +------+---------------------+------------------------------------+
    | 3    | Egress-QoS-Profile  | The name of an egress QoS profile  |
    +------+---------------------+------------------------------------+
    | 4    | User-ACL-Policy     | The name of an ACL policy          |
    +------+---------------------+------------------------------------+
    | 5    | Multicast-ProfileV4 | The name of an IPv4 multicast      |
    |      |                     | profile                            |
    +------+---------------------+------------------------------------+
    | 6    | Multicast-ProfileV6 | The name of an IPv6 multicast      |
    |      |                     | profile                            |
    +------+---------------------+------------------------------------+
    | 9    | NAT-Instance        | The name of a NAT instance         |
    +------+---------------------+------------------------------------+
    | 10   | Pool-Name           | The name of an address pool        |
    +------+---------------------+------------------------------------+

                           Table 4: Name Sub-TLVs

7.3.2.  Ingress-CAR Sub-TLV

   The Ingress-CAR sub-TLV indicates the authorized upstream Committed
   Access Rate (CAR) parameters.  The sub-TLV type of the Ingress-CAR
   sub-TLV is 7.  The sub-TLV length is 16.  The format is as shown in
   Figure 34.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  CIR (Committed Information Rate)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PIR (Peak Information Rate)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  CBS (Committed Burst Size)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PBS (Peak Burst Size)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 34: Ingress-CAR Sub-TLV

   Where:

      CIR (4 bytes):  Guaranteed rate in bits/second.

      PIR (4 bytes):  Burst rate in bits/second.

      CBS (4 bytes):  The token bucket in bytes.

      PBS (4 bytes):  Burst token bucket in bytes.

   These fields are unsigned integers.  More details about CIR, PIR,
   CBS, and PBS can be found in [RFC2698].

7.3.3.  Egress-CAR Sub-TLV

   The Egress-CAR sub-TLV indicates the authorized downstream Committed
   Access Rate (CAR) parameters.  The sub-TLV type of the Egress-CAR
   sub-TLV is 8.  Its sub-TLV length is 16 octets.  The format of the
   value part is as defined below.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  CIR (Committed Information Rate)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PIR (Peak Information Rate)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  CBS (Committed Burst Size)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PBS (Peak Burst Size)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 35: Egress-CAR Sub-TLV

   Where:

      CIR (4 bytes):  Guaranteed rate in bits/second.

      PIR (4 bytes):  Burst rate in bits/second.

      CBS (4 bytes):  The token bucket in bytes.

      PBS (4 bytes):  Burst token bucket in bytes.

   These fields are unsigned integers.  More details about CIR, PIR,
   CBS, and PBS can be found in [RFC2698].

7.3.4.  If-Desc Sub-TLV

   The If-Desc sub-TLV is defined to designate an interface.  It is an
   optional sub-TLV that may be carried in those TLVs that have an If-
   Index or Out-If-Index field.  The If-Desc sub-TLV is used as a
   locally unique identifier within a BNG.

   The sub-TLV type is 11.  The sub-TLV length is 12 octets.  The format
   depends on the If-Type (Section 8.6).  The format of the value part
   is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  If-Type (1-5)|    Chassis    |             Slot              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Sub-Slot            |            Port Number        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Sub-Port Number                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    If-Desc Sub-TLV (Physical Port)

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | If-Type (6-7) |                Reserved                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Logic-ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Sub-Port Number                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     If-Desc Sub-TLV (Virtual Port)

                     Figure 36: If-Desc Sub-TLV Formats

   Where:

      If-Type:  8 bits in length.  The value of this field indicates the
         type of an interface.  The If-Type values defined in this
         document are listed in Section 8.6.

      Chassis (8 bits):  Identifies the chassis that the interface
         belongs to.

      Slot (16 bits):  Identifies the slot that the interface belongs
         to.

      Sub-Slot (16 bits):  Identifies the sub-slot the interface belongs
         to.

      Port Number (16 bits):  An identifier of a physical port/interface
         (e.g., If-Type: 1-5).  It is locally significant within the
         slot/sub-slot.

      Sub-Port Number (32 bits):  An identifier of the sub-port.
         Locally significant within its "parent" port (physical or
         virtual).

      Logic-ID (32 bits):  An identifier of a virtual interface (e.g.,
         If-Type: 6-7).

7.3.5.  IPv6 Address List Sub-TLV

   The IPv6 Address List sub-TLV is used to convey one or more IPv6
   addresses.  It is carried in the IPv6 Subscriber TLV.  The sub-TLV
   type is 12.  The sub-TLV length is variable.

   The format of the value part of the IPv6 Address List sub-TLV is as
   follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        IPv6 Address                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        IPv6 Address                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                            ...                                ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        IPv6 Address                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 37: IPv6 Address List Sub-TLV

   Where:

      IPv6 Address (IPv6-Address):  Each IP Address is of type IP-
         Address and carries an IPv6 address and length.

7.3.6.  Vendor Sub-TLV

   The Vendor sub-TLV is intended to be used inside the Value portion of
   the Vendor TLV (Section 7.13).  It provides a Sub-Type that
   effectively extends the sub-TLV type in the sub-TLV header and
   provides for versioning of Vendor sub-TLVs.

   The value part of the Vendor sub-TLV is formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Vendor-ID                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Sub-Type            |       Sub-Type-Version        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~             Value (other as specified by vendor)              ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 38: Vendor Sub-TLV

   Where:

      Sub-TLV type:  13.

      Sub-TLV length:  Variable.

      Vendor-ID (4 bytes):  Vendor ID as defined in RADIUS [RFC2865].

      Sub-Type (2 bytes):  Used by the vendor to distinguish multiple
         different sub-TLVs.

      Sub-Type-Version (2 bytes):  Used by the vendor to distinguish
         different versions of a vendor-defined sub-TLV Sub-Type.

      Value:  As specified by the vendor.

   Since vendor code will be handling the sub-TLV after the Vendor-ID
   field is recognized, the remainder of the sub-TLV can be organized
   however the vendor wants.  But it desirable for a vendor to be able
   to define multiple different Vendor sub-TLVs and to keep track of
   different versions of its vendor-defined sub-TLVs.  Thus, it is
   RECOMMENDED that the vendor assign a Sub-Type value for each of that
   vendor's sub-TLVs that is different from other Sub-Type values that
   vendor has used.  Also, when modifying a vendor-defined sub-TLV in a
   way potentially incompatible with a previous definition, the vendor
   SHOULD increase the value it is using in the Sub-Type-Version field.

7.4.  Hello TLV

   The Hello TLV is defined to be carried in the Hello message for
   version and capabilities negotiation.  It indicates the S-CUSP sub-
   version and capabilities supported.  The format of the value part of
   the Hello TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          VerSupported                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Vendor-ID                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Capabilities                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            Figure 39: Hello TLV

   Where:

      TLV type:  100.

      TLV length:  12 octets.

      VerSupported:  32 bits in length.  It is a bit map of the Sub-
         Versions of S-CUSP that the sender supports.  This document
         specifies Sub-Version zero of Major Version 1, that is, Version
         1.0.  The VerSupported field MUST be nonzero.  The VerSupported
         bits are numbered from 0 as the most significant bit.  Bit 0
         indicates support of Sub-Version zero, bit 1 indicates support
         of Sub-Version one, etc.

      Vendor-ID:  4 bytes in length.  Vendor ID, as defined in RADIUS
         [RFC2865].

      Capabilities:  32 bits in length.  Flags that indicate the support
         of particular capabilities by the sender of the Hello.  No
         capabilities are defined in this document, so implementations
         of the version specified herein will set this field to zero.
         The Capabilities field of the Hello TLV MUST be checked before
         any other TLVs in the Hello because capabilities defined in the
         future might extend existing TLVs or permit new TLVs.

   After the exchange of Hello messages, the CP and UP each perform a
   logical AND of the Sub-Version supported by the CP and the UP and
   separately perform a logical AND of the Capabilities field for the CP
   and the UP.

   If the result of the AND of the Sub-Versions supported is zero, then
   no session can be established, and the connection is torn down.  If
   the result of the AND of the Sub-Versions supported is nonzero, then
   the session uses the highest Sub-Version supported by both the CP and
   UP.

   For example, if one side supports Sub-Versions 1, 3, 4, and 5
   (VerSupported = 0x5C000000) and the other side supports 2, 3, and 4
   (VerSupported = 0x38000000), then 3 and 4 are the Sub-Versions in
   common, and 4 is the highest Sub-Version supported by both sides.  So
   Sub-Version 4 is used for the session that has been negotiated.

   The result of the logical AND of the Capabilities bits will show what
   additional capabilities both sides support.  If this result is zero,
   there are no such capabilities, so none can be used during the
   session.  If this result is nonzero, it shows the additional
   capabilities that can be used during the session.  The CP and the UP
   MUST NOT use a capability unless both advertise support.

7.5.  Keepalive TLV

   The Keepalive TLV is carried in the Hello message.  It provides
   timing information for this feature.  The format of the value part of
   the Keepalive TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Keepalive   | DeadTimer     |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 40: Keepalive TLV

   Where:

      TLV type:  102.

      TLV length:  4 octets.

      Keepalive (8 bits):  Indicates the maximum interval (in seconds)
         between two consecutive S-CUSP messages sent by the sender of
         the message containing this TLV as an unsigned integer.  The
         minimum value for the Keepalive field is 1 second.  When set to
         0, once the session is established, no further Keepalive
         messages are sent to the remote peer.  A RECOMMENDED value for
         the Keepalive frequency is 30 seconds.

      DeadTimer (8 bits in length):  Specifies the amount of time as an
         unsigned integer number of seconds, after the expiration of
         which, the S-CUSP peer can declare the session with the sender
         of the Hello message to be down if no S-CUSP message has been
         received.  The DeadTimer SHOULD be set to 0 and MUST be ignored
         if the Keepalive is set to 0.  A RECOMMENDED value for the
         DeadTimer is 4 times the value of the Keepalive.

      Reserved:  The Reserved bits MUST be sent as zero and ignored on
         receipt.

7.6.  Error Information TLV

   The Error Information TLV is a common TLV that can be used in many
   responses (e.g., Update_Response message) and ACK messages (e.g.,
   Addr_Allocation_Ack message).  It is used to convey the information
   about an error in the received S-CUSP message.  The format of the
   value part of the Error Information TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Message-Type  |  Reserved             |  TLV-Type             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Error Code                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 41: Error Information TLV

   Where:

      TLV type:  101.

      TLV length:  8 octets.

      Message-Type (1 byte):  This parameter is the message type of the
         message containing an error.

      Reserved (1 byte):  MUST be sent as zero and ignored on receipt.

      TLV-Type (2 bytes):  Indicates which TLV caused the error.

      Error Code:  4 bytes in length.  Indicate the specific Error Code
         (see Section 8.5).

7.7.  BAS Function TLV

   The BAS Function TLV is used by a CP to control the access mode,
   authentication methods, and other related functions of an interface
   on a UP.

   The format of the BAS Function TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          If-Index                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Access-Mode  |  Auth-Method4 |  Auth-Method6 |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Sub-TLVs (optional)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 42: BAS Function TLV

   Where:

      TLV type:  1.

      TLV length:  Variable.

      If-Index:  4 bytes in length, a unique identifier of an interface
         of a BNG.

      Access-Mode:  1 byte in length.  It indicates the access mode of
         the interface.  The defined values are listed in Section 8.7.

      Auth-Method4:  1 byte in length.  It indicates the authentication
         on this interface for the IPv4 scenario.  This field is defined
         as a bitmap.  The bits defined in this document are listed in
         Section 8.8.  Other bits are reserved and MUST be sent as zero
         and ignored on receipt.

      Auth-Method6:  1 byte in length.  It indicates the authentication
         on this interface for the IPv6 scenario.  This field is defined
         as a bitmap.  The bits defined in this document are listed in
         Section 8.8.  Other bits are reserved and MUST be sent as zero
         and ignored on receipt.

      Sub-TLVs:  The IF-Desc sub-TLV can be carried.

         If-Desc sub-TLV:  Carries the interface information.

      Flags:  The Flags field is defined as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                MBZ                            |Y|X|P|I|N|A|S|F|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 43: Interface Flags

   Where:

      F (IPv4 Trigger) bit:  Indicates whether IPv4 packets can trigger
         a subscriber to go online.

         1:  Enabled.

         0:  Disabled.

      S (IPv6 Trigger) bit:  Indicates whether IPv6 packets can trigger
         a subscriber to go online.

         1:  Enabled.

         0:  Disabled.

      A (ARP Trigger) bit:  Indicates whether ARP packets can trigger a
         subscriber to go online.

         1:  Enabled.

         0:  Disabled.

      N (ND Trigger) bit:  Indicates whether ND packets can trigger a
         subscriber to go online.

         1:  Enabled.

         0:  Disabled.

      I (IPoE-Flow-Check):  Used for UP detection.

         1:  Enable traffic detection.

         0:  Disable traffic detection.

      P (PPP-Flow-Check) bit:  Used for UP detection.

         1:  Enable traffic detection.

         0:  Disable traffic detection.

      X (ARP-Proxy) bit:  Indicates whether ARP proxy is enabled on the
         interface.

         1:  The interface is enabled with ARP proxy and can process ARP
            requests across different network ports and VLANs.

         0:  The ARP proxy is not enabled on the interface and only the
            ARP requests of the same network port and VLAN are
            processed.

      Y (ND-Proxy) bit:  Indicates whether ND proxy is enabled on the
         interface.

         1:  The interface is enabled with ND proxy and can process ND
            requests across different network ports and VLANs.

         0:  The ND proxy is not enabled on the interface and only the
            ND requests of the same network port and VLAN are processed.

      MBZ:  Reserved bits that MUST be sent as zero and ignored on
         receipt.

7.8.  Routing TLVs

   Typically, after an S-CUSP session is established between a UP and a
   CP, the CP will allocate one or more blocks of IP addresses to the
   UP.  Those IP addresses will be allocated to subscribers who will
   dial-up (as defined in Section 4.3.1) to the UP.  To make sure that
   other nodes within the network learn how to reach those IP addresses,
   the CP needs to install one or more routes that can reach those IP
   addresses on the UP and notify the UP to advertise the routes to the
   network.

   The Routing TLVs are used by a CP to notify a UP of the updates to
   network routing information.  They can be carried in the
   Update_Request message and Sync_Data message.

7.8.1.  IPv4 Routing TLV

   The IPv4 Routing TLV is used to carry information related to IPv4
   network routing.

   The format of the TLV value part is as below:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Dest-Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Next-Hop                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Out-If-Index                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Cost                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Tag                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Route-Type             |          Reserved           |A|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Sub-TLVs  (optional)                 ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 44: IPv4 Routing TLV

   Where:

      TLV type:  7.

      TLV length:  Variable.

      User-ID:  4 bytes in length.  This field carries the user
         identifier.  It is filled with all Fs when a non-user route is
         delivered to the UP.

      Dest-Address (IPv4-Address type):  Identifies the destination
         address.

      Next-Hop (IPv4-Address type):  Identifies the next-hop address.

      Out-If-Index (4 bytes):  Indicates the interface index.

      Cost (4 bytes):  The cost value of the route.

      Tag (4 bytes):  The tag value of the route.

      Route-Type (2 bytes):  The value of this field indicates the route
         type.  The values defined in this document are listed in
         Section 8.9.

      Advertise-Flag:  1 bit shown as "A" in the figure above
         (Figure 44).  Indicates whether the UP should advertise the
         route.  The following flag values are defined:

         0:  Not advertised.

         1:  Advertised.

      Sub-TLVs:  The VRF-Name and/or If-Desc sub-TLVs can be carried.

         VRF-Name sub-TLV:  Indicates which VRF the route belongs to.

         If-Desc sub-TLV:  Carries the interface information.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.8.2.  IPv6 Routing TLV

   The IPv6 Routing TLV is used to carry IPv6 network routing
   information.

   The format of the value part of this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          IPv6 Dest-Address                    ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          IPv6 Next-Hop                        ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Out-If-Index                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Cost                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Tag                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Route-Type             |          Reserved           |A|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Sub-TLVs (optional)                  ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 45: IPv6 Routing TLV

   Where:

      TLV type:  8.

      TLV length:  Variable.

      User-ID:  4 bytes in length.  This field carries the user
         identifier.  This field is filled with all Fs when a non-user
         route is delivered to the UP.

      IPv6 Dest-Address (IPv6-Address type):  Identifies the destination
         address.

      IPv6 Next-Hop (IPv6-Address type):  Identifies the next-hop
         address.

      Out-If-Index (4 bytes):  Indicates the interface index.

      Cost (4 bytes):  This is the cost value of the route.

      Tag (4 bytes):  The tag value of the route.

      Route-Type (2 bytes):  The value of this field indicates the route
         type.  The values defined in this document are listed in
         Section 8.9.

      Advertise-Flag:  1 bit shown as "A" in the figure above
         (Figure 45).  Indicates whether the UP should advertise the
         route.  The following flags are defined:

         0:  Not advertised.

         1:  Advertised.

      Sub-TLVs:  The If-Desc and VRF-Name sub-TLVs can be carried.

         VRF-Name sub-TLV:  Indicates the VRF to which the subscriber
            belongs.

         If-Desc sub-TLV:  Carries the interface information.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.  Subscriber TLVs

   The Subscriber TLVs are defined for a CP to send the basic
   information about a user to a UP.

7.9.1.  Basic Subscriber TLV

   The Basic Subscriber TLV is used to carry the common information for
   all kinds of access subscribers.  It is carried in an Update_Request
   message.

   The format of the Basic Subscriber TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Session-ID                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-MAC                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        User-MAC (cont.)       |   Oper-ID     |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Access-Type   |Sub-Access-Type|  Account-Type | Address Family|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               C-VID           |          P-VID                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Detect-Times    |          Detect-Interval      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            If-Index                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                            Sub-TLVs (optional)                ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 46: Basic Subscriber TLV

   Where:

      TLV type:  2.

      TLV length:  Variable.

      User-ID (4 bytes):  The identifier of a subscriber.

      Session-ID (4 bytes):  Session ID of a PPPoE subscriber.  The
         value zero identifies a non-PPPoE subscriber.

      User-MAC (MAC-Addr type):  The MAC address of a subscriber.

      Oper-ID (1 byte):  Indicates the ID of an operation performed by a
         user.  This field is carried in the response from the UP.

      Reserved (1 byte):  MUST be sent as zero and ignored on receipt.

      Access-Type (1 byte):  Indicates the type of subscriber access.
         Values defined in this document are listed in Section 8.10.

      Sub-Access-Type (1 byte):  Indicates whether PPP termination or
         PPP relay is used.

         0:  Reserved.

         1:  PPP Relay (for LAC).

         2:  PPP termination (for LNS).

      Account-Type (1 byte):  Indicates whether traffic statistics are
         collected independently.

         0:  Collects statistics on IPv4 and IPv6 traffic of terminals
            independently.

         1:  Collects statistics on IPv4 and IPv6 traffic of terminals.

      Address Family (1 byte):  The type of IP address.

         1:  IPv4.

         2:  IPv6.

         3:  Dual stack.

      C-VID (VLAN-ID):  Indicates the inner VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  The default value of
         PRI is 7, the value of DEI is 0, and the value of VID is
         1-4094.  The PRI value can also be obtained by parsing terminal
         packets.

      P-VID (VLAN-ID):  Indicates the outer VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  The format is the same
         as that for C-VID.

      Detect-Times (2 bytes):  Number of detection timeout times.  The
         value 0 indicates that no detection is performed.

      Detect-Interval (2 bytes):  Detection interval in seconds.

      If-Index (4 bytes):  Interface index.

      Sub-TLVs:  The VRF-Name sub-TLV and If-Desc sub-TLV can be
         carried.

         VRF-Name sub-TLV:  Indicates the VRF to which the subscriber
            belongs.

         If-Desc sub-TLV:  Carries the interface information.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.2.  PPP Subscriber TLV

   The PPP Subscriber TLV is defined to carry PPP information of a user
   from a CP to a UP.  It will be carried in an Update_Request message
   when PPPoE or L2TP access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        MSS-Value              |        Reserved             |M|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        MRU                    |        Reserved               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Magic-Number                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Peer-Magic-Number                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 47: PPP Subscriber TLV

   Where:

      TLV type:  3.

      TLV length:  12 octets.

      User-ID (4 bytes):  The identifier of a subscriber.

      MSS-Value (2 bytes):  Indicates the MSS value (in bytes).

      MSS-Enable (M) (1 bit):  Indicates whether the MSS is enabled.

         0:  Disabled.

         1:  Enabled.

      MRU (2 bytes):  PPPoE local MRU (in bytes).

      Magic-Number (4 bytes):  Local magic number in PPP negotiation
         packets.

      Peer-Magic-Number (4 bytes):  Remote peer magic number.

      Reserved:  The Reserved fields MUST be sent as zero and ignored on
         receipt.

7.9.3.  IPv4 Subscriber TLV

   The IPv4 Subscriber TLV is defined to carry IPv4-related information
   for a BNG user.  It will be carried in an Update_Request message when
   IPv4 IPoE or PPPoE access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-IPv4                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Gateway-IPv4                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          MTU                  |   Reserved            |U|E|W|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          VRF-Name Sub-TLV                     ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 48: IPv4 Subscriber TLV

   Where:

      TLV type:  4.

      TLV length:  Variable.

      User-ID (4 bytes):  The identifier of a subscriber.

      User-IPv4 (IPv4-Address):  The IPv4 address of the subscriber.

      Gateway-IPv4 (IPv4-Address):  The gateway address of the
         subscriber.

      Portal-Force (P) (1 bit):  Push advertisement.

         0:  Off.

         1:  On.

      Web-Force (W) (1 bit):  Push IPv4 Web.

         0:  Off.

         1:  On.

      Echo-Enable (E) (1 bit):  UP returns ARP Req or PPP Echo.

         0:  Off.

         1:  On.

      IPv4-URPF (U) (1 bit):  User Unicast Reverse Path Forwarding
         (URPF) flag.

         0:  Off.

         1:  On.

      MTU (2 bytes):  MTU value.  The default value is 1500.

      VRF-Name Sub-TLV:  Indicates the subscriber belongs to which VRF.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.4.  IPv6 Subscriber TLV

   The IPv6 Subscriber TLV is defined to carry IPv6-related information
   for a BNG user.  It will be carried in an Update_Request message when
   IPv6 IPoE or PPPoE access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~           User PD-Address (IPv6 Address List Sub-TLV)         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~        Gateway ND-Address (IPv6 Address List Sub-TLV)         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User Link-Local-Address              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          IPv6 Interface ID                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          IPv6 Interface ID (cont.)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          MTU                  |   Reserved            |U|E|W|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                    VRF Name Sub-TLV (optional)                ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 49: IPv6 Subscriber TLV

   Where:

      TLV type:  5.

      TLV length:  Variable.

      User-ID (4 bytes):  The identifier of a subscriber.

      User PD-Addresses (IPv6 Address List):  Carries a list of Prefix
         Delegation (PD) addresses of the subscriber.

      User ND-Addresses (IPv6 Address List):  Carries a list of Neighbor
         Discovery (ND) addresses of the subscriber.

      User Link-Local-Address (IPv6-Address):  The link-local address of
         the subscriber.

      IPv6 Interface ID (8 bytes):  The identifier of an IPv6 interface.

      Portal-Force 1 bit (P):  Push advertisement.

         0:  Off.

         1:  On.

      Web-Force 1 bit (W):  Push IPv6 Web.

         0:  Off.

         1:  On.

      Echo-Enable 1 bit (E):  The UP returns ARP Req or PPP Echo.

         0:  Off.

         1:  On.

      IPv6-URPF 1 bit (U):  User Reverse Path Forwarding (URPF) flag.

         0:  Off.

         1:  On.

      MTU (2 bytes):  The MTU value.  The default value is 1500.

      VRF-Name Sub-TLV:  Indicates the VRF to which the subscriber
         belongs.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.5.  IPv4 Static Subscriber Detect TLV

   The IPv4 Static Subscriber Detect TLV is defined to carry
   IPv4-related information for a static access subscriber.  It will be
   carried in an Update_Request message when IPv4 static access on a UP
   needs to be enabled.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          If-Index                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           C-VID               |           P-VID               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Gateway Address                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-MAC                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        User-MAC (cont.)       |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       Sub-TLVs (optional)                     ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 50: IPv4 Static Subscriber TLV

   Where:

      TLV type:  9.

      TLV length:  Variable.

      If-Index (4 bytes):  The interface index of the interface from
         which the subscriber will dial-up.

      C-VID (VLAN-ID):  Indicates the inner VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  A valid value is
         1-4094.

      P-VID (VLAN-ID):  Indicates the outer VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  The format is the same
         as that of the C-VID.  A valid value is 1-4094.

      User Address (IPv4-Addr):  The user's IPv4 address.

      Gateway Address (IPv4-Addr):  The gateway's IPv4 address.

      User-MAC (MAC-Addr type):  The MAC address of the subscriber.

      Sub-TLVs:  The VRF-Name and If-Desc sub-TLVs may be carried.

         VRF-Name sub-TLV:  Indicates the VRF to which the subscriber
            belongs.

         If-Desc sub-TLV:  Carries the interface information.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.6.  IPv6 Static Subscriber Detect TLV

   The IPv6 Static Subscriber Detect TLV is defined to carry
   IPv6-related information for a static access subscriber.  It will be
   carried in an Update_Request message when needed to enable IPv6
   static subscriber detection on a UP.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          If-Index                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           C-VID               |           P-VID               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          User Address                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Gateway Address                      ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-MAC                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        User-MAC (cont.)       |           Reserved            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        Sub-TLVs (optional)                     ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 51: IPv6 Static Subscriber Detect TLV

   Where:

      TLV type:  10.

      TLV length:  Variable.

      If-Index (4 bytes):  The interface index of the interface from
         which the subscriber will dial-up.

      C-VID (VLAN-ID):  Indicates the inner VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  A valid value is
         1-4094.

      P-VID (VLAN-ID):  Indicates the outer VLAN ID.  The value 0
         indicates that the VLAN ID is invalid.  The format is the same
         as that the of C-VID.  A valid value is 1-4094.

      User Address (IPv6-Address type):  The subscriber's IPv6 address.

      Gateway Address (IPv6-Address type):  The gateway's IPv6 Address.

      User-MAC (MAC-Addr type):  The MAC address of the subscriber.

      Sub-TLVs:  VRF-Name and If-Desc sub-TLVs may be carried

         VRF-Name sub-TLV:  Indicates the VRF to which the subscriber
            belongs.

         If-Desc sub-TLV:  Carries the interface information.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.7.  L2TP-LAC Subscriber TLV

   The L2TP-LAC Subscriber TLV is defined to carry the related
   information for an L2TP LAC access subscriber.  It will be carried in
   an Update_Request message when L2TP LAC access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Local-Tunnel-ID          |     Local-Session-ID          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Remote-Tunnel-ID         |     Remote-Session-ID         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 52: L2TP-LAC Subscriber TLV

   Where:

      TLV type:  11.

      TLV length:  12 octets.

      User-ID (4 bytes):  The identifier of a user/subscriber.

      Local-Tunnel-ID (2 bytes):  The local ID of the L2TP tunnel.

      Local-Session-ID (2 bytes):  The local session ID with the L2TP
         tunnel.

      Remote-Tunnel-ID (2 bytes):  The identifier of the L2TP tunnel at
         the remote endpoint.

      Remote-Session-ID (2 bytes):  The session ID of the L2TP tunnel at
         the remote endpoint.

7.9.8.  L2TP-LNS Subscriber TLV

   The L2TP-LNS Subscriber TLV is defined to carry the related
   information for a L2TP LNS access subscriber.  It will be carried in
   an Update_Request message when L2TP LNS access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Local-Tunnel-ID          |     Local-Session-ID          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Remote-Tunnel-ID         |     Remote-Session-ID         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 53: L2TP-LNS Subscriber TLV

   Where:

      TLV type:  12.

      TLV length:  12 octets.

      User-ID (4 bytes):  The identifier of a user/subscriber.

      Local-Tunnel-ID (2 bytes):  The local ID of the L2TP tunnel.

      Local-Session-ID (2 bytes):  The local session ID with the L2TP
         tunnel.

      Remote-Tunnel-ID (2 bytes):  The identifier of the L2TP tunnel at
         the remote endpoint.

      Remote-Session-ID (2 bytes):  The session ID of the L2TP tunnel at
         the remote endpoint.

7.9.9.  L2TP-LAC Tunnel TLV

   The L2TP-LAC Tunnel TLV is defined to carry information related to
   the L2TP LAC tunnel.  It will be carried in the Update_Request
   message when L2TP LAC access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       Local-Tunnel-ID         |       Remote-Tunnel-ID        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Source-Port         |           Dest-Port           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Source-IP                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Dest-IP                              ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          VRF-Name Sub-TLV                     ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 54: L2TP-LAC Tunnel TLV

   Where:

      TLV type:  13.

      TLV length:  Variable.

      Local-Tunnel-ID (2 bytes):  The local ID of the L2TP tunnel.

      Remote-Tunnel-ID (2 bytes):  The remote ID of the L2TP tunnel.

      Source-Port (2 bytes):  The source UDP port number of an L2TP
         subscriber.

      Dest-Port (2 bytes):  The destination UDP port number of an L2TP
         subscriber.

      Source-IP (IPv4/v6):  The source IP address of the tunnel.

      Dest-IP (IPv4/v6):  The destination IP address of the tunnel.

      VRF-Name Sub-TLV:  The VRF name to which the L2TP subscriber
         tunnel belongs.

7.9.10.  L2TP-LNS Tunnel TLV

   The L2TP-LNS Tunnel TLV is defined to carry information related to
   the L2TP LNS tunnel.  It will be carried in the Update_Request
   message when L2TP LNS access is used.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Local-Tunnel-ID        |       Remote-Tunnel-ID        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Source-Port            |         Dest-Port             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       Source-IP                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       Dest-IP                                 ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       VRF-Name Sub-TLV                        ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 55: L2TP-LNS Tunnel TLV

   Where:

      TLV type:  14.

      TLV length:  Variable.

      Local-Tunnel-ID (2 bytes):  The local ID of the L2TP tunnel.

      Remote-Tunnel-ID (2 bytes):  The remote ID of the L2TP tunnel.

      Source-Port (2 bytes):  The source UDP port number of an L2TP
         subscriber.

      Dest-Port (2 bytes):  The destination UDP port number of an L2TP
         subscriber.

      Source-IP (IPv4/v6):  The source IP address of the tunnel.

      Dest-IP (IPv4/v6):  The destination IP address of the tunnel.

      VRF-Name Sub-TLV:  The VRF name to which the L2TP subscriber
         tunnel belongs.

7.9.11.  Update Response TLV

   The Update Response TLV is used to return the operation result of an
   update request.  It is carried in the Update_Response message as a
   response to the Update_Request message.

   The format of the value part of the Update Response TLV is as
   follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          User-ID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | User-Trans-ID |   Oper-Code   |   Oper-Result |  Reserved     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Error-Code                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 56: Update Response TLV

   Where:

      TLV type:  302.

      TLV length:  12.

      User-ID (4 bytes):  A unique identifier of a user/subscriber.

      User-Trans-ID (1 byte):  In the case of dual-stack access or when
         modifying a session, User-Trans-ID is used to identify a user
         operation transaction.  It is used by the CP to correlate a
         response to a specific request.

      Oper-Code (1 byte):  Operation code.

         1:  Update.

         2:  Delete.

      Oper-Result (1 byte):  Operation Result.

         0:  Success.

         Others:  Failure.

      Error-Code (4 bytes):  Operation failure cause code.  For details,
         see Section 8.5.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.12.  Subscriber Policy TLV

   The Subscriber Policy TLV is used to carry the policies that will be
   applied to a subscriber.  It is carried in the Update_Request
   message.

   The format of the TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   I-Priority  |   E-Priority  |   Reserved                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Sub-TLVs                             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 57: Subscriber Policy TLV

   Where:

      TLV type:  6.

      TLV length:  Variable.

      User-ID (4 bytes):  The identifier of a user/subscriber.

      Ingress-Priority (1 byte):  Indicates the upstream priority.  The
         value range is 0~7.

      Egress-Priority (1 byte):  Indicates the downstream priority.  The
         value range is 0~7.

      Sub-TLVs:  The sub-TLVs that are present can occur in any order.

         Ingress-CAR sub-TLV:  Upstream CAR.

         Egress-CAR sub-TLV:  Downstream CAR.

         Ingress-QoS-Profile sub-TLV:  Indicates the name of the QoS-
            Profile that is the profile in the upstream direction.

         Egress-QoS-Profile sub-TLV:  Indicates the name of the QoS-
            Profile that is the profile in the downstream direction.

         User-ACL-Policy sub-TLV:  All ACL user policies, including
            v4ACLIN, v4ACLOUT, v6ACLIN, v6ACLOUT, v4WEBACL, v6WEBACL,
            v4SpecialACL, and v6SpecialACL.

         Multicast-Profile4 sub-TLV:  IPv4 multicast policy name.

         Multicast-Profile6 sub-TLV:  IPv6 multicast policy name.

         NAT-Instance sub-TLV:  Indicates the instance ID of a NAT user.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.9.13.  Subscriber CGN Port Range TLV

   The Subscriber CGN Port Range TLV is used to carry the NAT public
   address and port range.  It will be carried in the Update_Response
   message when CGN is used.

   The format of the value part of this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            User-ID                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           NAT-Port-Start      |          NAT-Port-End         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            NAT-Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 58: Subscriber CGN Port Range TLV

   Where:

      TLV type:  15.

      TLV length:  12 octets.

      User-ID (4 bytes):  The identifier of a user/subscriber.

      NAT-Port-Start (2 bytes):  The start port number.

      NAT-Port-End (2 bytes):  The end port number.

      NAT-Address (4 bytes):  The NAT public network address.

7.10.  Device Status TLVs

   The TLVs in this section are for reporting interface and board-level
   information from the UP to the CP.

7.10.1.  Interface Status TLV

   The Interface Status TLV is used to carry the status information of
   an interface on a UP.  It is carried in a Report message.

   The format of the value part of this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          If-Index                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          MAC-Address (upper part)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   MAC-Address (lower part)    |   Phy-State   |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          MTU                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Sub-TLVs (optional)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 59: Interface Status TLV

   Where:

      TLV type:  200.

      TLV length:  Variable.

      If-Index (4 bytes):  Indicates the interface index.

      MAC-Address (MAC-Addr type):  Interface MAC address.

      Phy-State (1 byte):  Physical status of the interface.

         0:  Down.

         1:  Up.

      MTU (4 bytes):  Interface MTU value.

      Sub-TLVs:  The If-Desc and VRF-Name sub-TLVs can be carried.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.10.2.  Board Status TLV

   The Board Status TLV is used to carry the status information of a
   board on an UP.  It is carried in a Report message.

   The format of the value part of the Board Status TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Board-Type  | Board-State   |   Reserved    |   Chassis     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Slot            |           Sub-Slot            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 60: Board Status TLV

   Where:

      TLV type:  201.

      TLV length:  8 octets.

      Chassis (1 byte):  The chassis number of the board.

      Slot (16 bits):  The slot number of the board.

      Sub-Slot (16 bits):  The sub-slot number of the board.

      Board-Type (1 byte):  The type of board used.

         1:  CGN Service Process Unit (SPU) board.

         2:  Line Process Unit (LPU) board.

      Board-State (1 byte):  Indicates whether there are issues with the
         board.

         0:  Normal.

         1:  Abnormal.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.11.  CGN TLVs

7.11.1.  Address Allocation Request TLV

   The Address Allocation Request TLV is used to request address
   allocation from the CP.  A Pool-Name sub-TLV is carried to indicate
   from which address pool to allocate addresses.  The Address
   Allocation Request TLV is carried in the Addr_Allocation_Req message.

   The format of the value part of this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                          Pool-Name Sub-TLV                    ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 61: Address Allocation Request TLV

   Where:

      TLV type:  400.

      TLV length:  Variable.

      Pool-Name sub-TLV:  Indicates from which address pool to allocate
         address.

7.11.2.  Address Allocation Response TLV

   The Address Allocation Response TLV is used to return the address
   allocation result; it is carried in the Addr_Allocation_Ack message.

   The value part of the Address Allocation Response TLV is formatted as
   follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Lease Time                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Client-IP                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Client-IP (cont.)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Error-Code                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        Pool-Name Sub-TLV                      ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 62: Address Allocation Response TLV

   Where:

      TLV type:  401.

      TLV length:  Variable.

      Lease Time (4 bytes):  Duration of address lease in seconds.

      Client-IP (IPv4-Address type):  The allocated IPv4 address and
         mask.

      Error-Code (4 bytes):  Indicates success or an error.

         0:  Success.

         1:  Failure.

         3001:  Pool-Mismatch.  The corresponding address pool cannot be
            found.

         3002:  Pool-Full.  The address pool is fully allocated, and no
            address segment is available.

      Pool-Name sub-TLV:  Indicates from which address pool the address
         is allocated.

7.11.3.  Address Renewal Request TLV

   The Address Renewal Request TLV is used to request address renewal
   from the CP.  It is carried in the Addr_Renew_Req message.

   The format of this TLV value is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP (cont.)                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                     Pool-Name Sub-TLV                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 63: Address Renewal Request TLV

   Where:

      TLV type:  402.

      TLV length:  Variable.

      Client-IP (IPv4-Address type):  The IPv4 address and mask to be
         renewed.

      Pool-Name sub-TLV:  Indicates from which address pool to renew the
         address.

7.11.4.  Address Renewal Response TLV

   The Address Renewal Response TLV is used to return the address
   renewal result.  It is carried in the Addr_Renew_Ack message.

   The format of this TLV value is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP (cont.)                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Error-Code                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                     Pool-Name Sub-TLV                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 64: Address Renewal Response TLV

   Where:

      TLV type:  403.

      TLV length:  Variable.

      Client-IP (IPv4-Address type):  The renewed IPv4 address and mask.

      Error-Code (4 bytes):  Indicates success or an error:

         0:  Success.

         1:  Failure.

         3001:  Pool-Mismatch.  The corresponding address pool cannot be
            found.

         3002:  Pool-Full.  The address pool is fully allocated, and no
            address segment is available.

         3003:  Subnet-Mismatch.  The address pool subnet cannot be
            found.

         3004:  Subnet-Conflict.  Subnets in the address pool have been
            assigned to other clients.

      Pool-Name sub-TLV:  Indicates from which address pool to renew the
         address.

7.11.5.  Address Release Request TLV

   The Address Release Request TLV is used to release an IPv4 address.
   It is carried in the Addr_Release_Req message.

   The value part of this TLV is formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP (cont.)                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                     Pool-Name sub-TLV                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 65: Address Release Request TLV

   Where:

      TLV type:  404.

      TLV length:  Variable.

      Client-IP (IPv4-Address type):  The IPv4 address and mask to be
         released.

      Pool-Name sub-TLV:  Indicates from which address pool to release
         the address.

7.11.6.  Address Release Response TLV

   The Address Release Response TLV is used to return the address
   release result.  It is carried in the Addr_Release_Ack message.

   The format of the value part of this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP                                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Client-IP (cont.)                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Error-Code                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                     Pool-Name sub-TLV                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 66: Address Release Response TLV

   Where:

      TLV type:  405.

      TLV length:  Variable.

      Client-IP (IPv4-Address type):  The released IPv4 address and
         mask.

      Error-Code (4 bytes):  Indicates success or an error.

         0:  Success.  Address release success.

         1:  Failure.  Address release failed.

         3001:  Pool-Mismatch.  The corresponding address pool cannot be
            found.

         3003:  Subnet-Mismatch.  The address cannot be found.

         3004:  Subnet-Conflict.  The address has been allocated to
            another subscriber.

      Pool-Name sub-TLV:  Indicates from which address pool to release
         the address.

7.12.  Event TLVs

7.12.1.  Subscriber Traffic Statistics TLV

   The Subscriber Traffic Statistics TLV is used to return the traffic
   statistics of a user/subscriber.  The format of the value part of
   this TLV is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                User-ID                                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Statistics-Type                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Packets (upper part)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Packets (lower part)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Bytes (upper part)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Bytes (lower part)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Loss Packets (upper part)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Loss Packets (lower part)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Loss Bytes (upper part)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Ingress Loss Bytes (lower part)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Packets (upper part)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Packets (lower part)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Bytes (upper part)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Bytes (lower part)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Loss Packets (upper part)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Loss Packets (lower part)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Loss Bytes (upper part)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Egress Loss Bytes (lower part)                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 67: Subscriber Traffic Statistics TLV

   Where:

      TLV type:  300.

      TLV length:  72 octets.

      User-ID (4 bytes):  The subscriber identifier.

      Statistics-Type (4 bytes):  Traffic type.  It can be one of the
         following options:

         0:  IPv4 traffic.

         1:  IPv6 traffic.

         2:  Dual-stack traffic.

      Ingress Packets (8 bytes):  The number of the packets in the
         upstream direction.

      Ingress Bytes (8 bytes):  The bytes of the upstream traffic.

      Ingress Loss Packets (8 bytes):  The number of the lost packets in
         the upstream direction.

      Ingress Loss Bytes (8 bytes):  The bytes of the lost upstream
         packets.

      Egress Packets (8 bytes):  The number of the packets in the
         downstream direction.

      Egress Bytes (8 bytes):  The bytes of the downstream traffic.

      Egress Loss Packets (8 bytes):  The number of the lost packets in
         the downstream direction.

      Egress Loss Bytes (8 bytes):  The bytes of the lost downstream
         packets.

7.12.2.  Subscriber Detection Result TLV

   The Subscriber Detection Result TLV is used to return the detection
   result of a subscriber.  Subscriber detection is a function to detect
   whether or not a subscriber is online.  The result can be used by the
   CP to determine how to deal with the subscriber session (e.g., delete
   the session if detection failed).

   The format of this TLV value part is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User-ID                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Detect-Type   | Detect-Result |          Reserved             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 68: Subscriber Detection Result TLV

   Where:

      TLV type:  301.

      TLV length:  8 octets.

      User-ID (4 bytes):  The subscriber identifier.

      Detect-Type (1 byte):  Type of traffic detected.

         0:  IPv4 detection.

         1:  IPv6 detection.

         2:  PPP detection.

      Detect-Result (1 byte):  Indicates whether the detection was
         successful.

         0:  Indicates that the detection is successful.

         1:  Detection failure.  The UP needs to report only when the
            detection fails.

      Reserved:  The Reserved field MUST be sent as zero and ignored on
         receipt.

7.13.  Vendor TLV

   The Vendor TLV occurs as the first TLV in the Vendor message
   (Section 6.6).  It provides a Sub-Type that effectively extends the
   message type in the message header, provides for versioning of vendor
   TLVs, and can accommodate sub-TLVs.

   The value part of the Vendor TLV is formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Vendor-ID                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Sub-Type            |       Sub-Type-Version        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                      Sub-TLVs (optional)                      ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 69: Vendor TLV

   Where:

      TLV type:  1024.

      TLV length:  Variable.

      Vendor-ID (4 bytes):  Vendor ID as defined in RADIUS [RFC2865].

      Sub-Type (2 bytes):  Used by the vendor to distinguish multiple
         different vendor messages.

      Sub-Type-Version (2 bytes):  Used by the vendor to distinguish
         different versions of a vendor-defined message Sub-Type.

      Sub-TLVs (variable):  Sub-TLVs as specified by the vendor.

   Since vendor code will be handling the TLV after the Vendor-ID field
   is recognized, the remainder of the TLV values can be organized
   however the vendor wants.  But it is desirable for a vendor to be
   able to define multiple different vendor messages and to keep track
   of different versions of its vendor-defined messages.  Thus, it is
   RECOMMENDED that the vendor assign a Sub-Type value for each vendor
   message that it defines different from other Sub-Type values that
   vendor has used.  Also, when modifying a vendor-defined message in a
   way potentially incompatible with a previous definition, the vendor
   SHOULD increase the value it is using in the Sub-Type-Version field.

8.  Tables of S-CUSP Codepoints

   This section provides tables of the S-CUSP codepoints, particularly
   message types, TLV types, TLV operation codes, sub-TLV types, and
   error codes.  In most cases, references are provided to relevant
   sections elsewhere in this document.

8.1.  Message Types

       +---------+---------------------+--------------------------+
       | Type    | Name                | Section of This Document |
       +=========+=====================+==========================+
       | 0       | Reserved            |                          |
       +---------+---------------------+--------------------------+
       | 1       | Hello               | 6.2.1                    |
       +---------+---------------------+--------------------------+
       | 2       | Keepalive           | 6.2.2                    |
       +---------+---------------------+--------------------------+
       | 3       | Sync_Request        | 6.2.3                    |
       +---------+---------------------+--------------------------+
       | 4       | Sync_Begin          | 6.2.4                    |
       +---------+---------------------+--------------------------+
       | 5       | Sync_Data           | 6.2.5                    |
       +---------+---------------------+--------------------------+
       | 6       | Sync_End            | 6.2.6                    |
       +---------+---------------------+--------------------------+
       | 7       | Update_Request      | 6.2.7                    |
       +---------+---------------------+--------------------------+
       | 8       | Update_Response     | 6.2.8                    |
       +---------+---------------------+--------------------------+
       | 9       | Report              | 6.4                      |
       +---------+---------------------+--------------------------+
       | 10      | Event               | 6.3                      |
       +---------+---------------------+--------------------------+
       | 11      | Vendor              | 6.6                      |
       +---------+---------------------+--------------------------+
       | 12      | Error               | 6.7                      |
       +---------+---------------------+--------------------------+
       | 13-199  | Unassigned          |                          |
       +---------+---------------------+--------------------------+
       | 200     | Addr_Allocation_Req | 6.5.1                    |
       +---------+---------------------+--------------------------+
       | 201     | Addr_Allocation_Ack | 6.5.2                    |
       +---------+---------------------+--------------------------+
       | 202     | Addr_Renew_Req      | 6.5.3                    |
       +---------+---------------------+--------------------------+
       | 203     | Addr_Renew_Ack      | 6.5.4                    |
       +---------+---------------------+--------------------------+
       | 204     | Addr_Release_Req    | 6.5.5                    |
       +---------+---------------------+--------------------------+
       | 205     | Addr_Release_Ack    | 6.5.6                    |
       +---------+---------------------+--------------------------+
       | 206-254 | Unassigned          |                          |
       +---------+---------------------+--------------------------+
       | 255     | Reserved            |                          |
       +---------+---------------------+--------------------------+

                          Table 5: Message Types

8.2.  TLV Types

      +-----------+-------------+-----------------------------------+
      | Type      | Name        | Usage Description                 |
      +===========+=============+===================================+
      | 0         | Reserved    | -                                 |
      +-----------+-------------+-----------------------------------+
      | 1         | BAS         | Carries the BNG access functions  |
      |           | Function    | to be enabled or disabled on      |
      |           |             | specified interfaces.             |
      +-----------+-------------+-----------------------------------+
      | 2         | Basic       | Carries the basic information     |
      |           | Subscriber  | about a BNG subscriber.           |
      +-----------+-------------+-----------------------------------+
      | 3         | PPP         | Carries the PPP information about |
      |           | Subscriber  | a BNG subscriber.                 |
      +-----------+-------------+-----------------------------------+
      | 4         | IPv4        | Carries the IPv4 address of a BNG |
      |           | Subscriber  | subscriber.                       |
      +-----------+-------------+-----------------------------------+
      | 5         | IPv6        | Carries the IPv6 address of a BNG |
      |           | Subscriber  | subscriber.                       |
      +-----------+-------------+-----------------------------------+
      | 6         | Subscriber  | Carries the policy information    |
      |           | Policy      | applied to a BNG subscriber.      |
      +-----------+-------------+-----------------------------------+
      | 7         | IPv4        | Carries the IPv4 network routing  |
      |           | Routing     | information.                      |
      +-----------+-------------+-----------------------------------+
      | 8         | IPv6        | Carries the IPv6 network routing  |
      |           | Routing     | information.                      |
      +-----------+-------------+-----------------------------------+
      | 9         | IPv4 Static | Carries the IPv4 static           |
      |           | Subscriber  | subscriber detect information.    |
      |           | Detect      |                                   |
      +-----------+-------------+-----------------------------------+
      | 10        | IPv6 Static | Carries the IPv6 static           |
      |           | Subscriber  | subscriber detect information.    |
      |           | Detect      |                                   |
      +-----------+-------------+-----------------------------------+
      | 11        | L2TP-LAC    | Carries the L2TP LAC subscriber   |
      |           | Subscriber  | information.                      |
      +-----------+-------------+-----------------------------------+
      | 12        | L2TP-LNS    | Carries the L2TP LNS subscriber   |
      |           | Subscriber  | information.                      |
      +-----------+-------------+-----------------------------------+
      | 13        | L2TP-LAC    | Carries the L2TP LAC tunnel       |
      |           | Tunnel      | subscriber information.           |
      +-----------+-------------+-----------------------------------+
      | 14        | L2TP-LNS    | Carries the L2TP LNS tunnel       |
      |           | Tunnel      | subscriber information.           |
      +-----------+-------------+-----------------------------------+
      | 15        | Subscriber  | Carries the public IPv4 address   |
      |           | CGN Port    | and related port range of a BNG   |
      |           | Range       | subscriber.                       |
      +-----------+-------------+-----------------------------------+
      | 16-99     | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+
      | 100       | Hello       | Used for version and Keepalive    |
      |           |             | timers negotiation.               |
      +-----------+-------------+-----------------------------------+
      | 101       | Error       | Carried in the Ack of the control |
      |           | Information | message.  Carries the processing  |
      |           |             | result, success, or error.        |
      +-----------+-------------+-----------------------------------+
      | 102       | Keepalive   | Carried in the Hello message for  |
      |           |             | Keepalive timers negotiation.     |
      +-----------+-------------+-----------------------------------+
      | 103-199   | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+
      | 200       | Interface   | Interfaces status reported by the |
      |           | Status      | UP including physical interfaces, |
      |           |             | sub-interfaces, trunk interfaces, |
      |           |             | and tunnel interfaces.            |
      +-----------+-------------+-----------------------------------+
      | 201       | Board       | Board information reported by the |
      |           | Status      | UP including the board type and   |
      |           |             | in-position status.               |
      +-----------+-------------+-----------------------------------+
      | 202-299   | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+
      | 300       | Subscriber  | User traffic statistics.          |
      |           | Traffic     |                                   |
      |           | Statistics  |                                   |
      +-----------+-------------+-----------------------------------+
      | 301       | Subscriber  | User detection information.       |
      |           | Detection   |                                   |
      |           | Result      |                                   |
      +-----------+-------------+-----------------------------------+
      | 302       | Update      | The processing result of a        |
      |           | Response    | subscriber session update.        |
      +-----------+-------------+-----------------------------------+
      | 303-299   | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+
      | 400       | Address     | Request address allocation.       |
      |           | Allocation  |                                   |
      |           | Request     |                                   |
      +-----------+-------------+-----------------------------------+
      | 401       | Address     | Address allocation response.      |
      |           | Allocation  |                                   |
      |           | Response    |                                   |
      +-----------+-------------+-----------------------------------+
      | 402       | Address     | Request for address lease         |
      |           | Renewal     | renewal.                          |
      |           | Request     |                                   |
      +-----------+-------------+-----------------------------------+
      | 403       | Address     | Response to a request for         |
      |           | Renewal     | extending an IP address lease.    |
      |           | Response    |                                   |
      +-----------+-------------+-----------------------------------+
      | 404       | Address     | Request to release the address.   |
      |           | Release     |                                   |
      |           | Request     |                                   |
      +-----------+-------------+-----------------------------------+
      | 405       | Address     | Ack of a message releasing an IP  |
      |           | Release     | address.                          |
      |           | Response    |                                   |
      +-----------+-------------+-----------------------------------+
      | 406-1023  | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+
      | 1024      | Vendor      | As implemented by the vendor.     |
      +-----------+-------------+-----------------------------------+
      | 1039-4095 | Unassigned  | -                                 |
      +-----------+-------------+-----------------------------------+

                             Table 6: TLV Types

8.3.  TLV Operation Codes

   TLV operation codes appear in the Oper field in the header of some
   TLVs.  See Section 7.1.

                           +------+------------+
                           | Code | Operation  |
                           +======+============+
                           | 0    | Reserved   |
                           +------+------------+
                           | 1    | Update     |
                           +------+------------+
                           | 2    | Delete     |
                           +------+------------+
                           | 3-15 | Unassigned |
                           +------+------------+

                           Table 7: TLV Operation
                                   Codes

8.4.  Sub-TLV Types

   See Section 7.3.

       +----------+---------------------+--------------------------+
       | Type     | Name                | Section of This Document |
       +==========+=====================+==========================+
       | 0        | Reserved            |                          |
       +----------+---------------------+--------------------------+
       | 1        | VRF Name            | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 2        | Ingress-QoS-Profile | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 3        | Egress-QoS-Profile  | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 4        | User-ACL-Policy     | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 5        | Multicast-ProfileV4 | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 6        | Multicast-ProfileV6 | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 7        | Ingress-CAR         | 7.3.2                    |
       +----------+---------------------+--------------------------+
       | 8        | Egress-CAR          | 7.3.3                    |
       +----------+---------------------+--------------------------+
       | 9        | NAT-Instance        | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 10       | Pool-Name           | 7.3.1                    |
       +----------+---------------------+--------------------------+
       | 11       | If-Desc             | 7.3.4                    |
       +----------+---------------------+--------------------------+
       | 12       | IPv6-Address List   | 7.3.5                    |
       +----------+---------------------+--------------------------+
       | 13       | Vendor              | 7.3.6                    |
       +----------+---------------------+--------------------------+
       | 12-64534 | Unassigned          |                          |
       +----------+---------------------+--------------------------+
       | 65535    | Reserved            |                          |
       +----------+---------------------+--------------------------+

                           Table 8: Sub-TLV Types

8.5.  Error Codes

   +-----------------+-----------------------+-------------------------+
   | Value           | Name                  | Remarks                 |
   +=================+=======================+=========================+
   | 0               | Success               | Success                 |
   +-----------------+-----------------------+-------------------------+
   | 1               | Failure               | Malformed message       |
   |                 |                       | received.               |
   +-----------------+-----------------------+-------------------------+
   | 2               | TLV-Unknown           | One or more of the      |
   |                 |                       | TLVs was not            |
   |                 |                       | understood.             |
   +-----------------+-----------------------+-------------------------+
   | 3               | TLV-Length            | The TLV length is       |
   |                 |                       | abnormal.               |
   +-----------------+-----------------------+-------------------------+
   | 4-999           | Unassigned            | Unassigned basic        |
   |                 |                       | error codes.            |
   +-----------------+-----------------------+-------------------------+
   | 1000            | Reserved              |                         |
   +-----------------+-----------------------+-------------------------+
   | 1001            | Version-Mismatch      | The version             |
   |                 |                       | negotiation fails.      |
   |                 |                       | Terminate.  The         |
   |                 |                       | subsequent service      |
   |                 |                       | processes               |
   |                 |                       | corresponding to the    |
   |                 |                       | UP are suspended.       |
   +-----------------+-----------------------+-------------------------+
   | 1002            | Keepalive Error       | The keepalive           |
   |                 |                       | negotiation fails.      |
   +-----------------+-----------------------+-------------------------+
   | 1003            | Timer Expires         | The establishment       |
   |                 |                       | timer expired.          |
   +-----------------+-----------------------+-------------------------+
   | 1004-1999       | Unassigned            | Unassigned error        |
   |                 |                       | codes for version       |
   |                 |                       | negotiation.            |
   +-----------------+-----------------------+-------------------------+
   | 2000            | Reserved              |                         |
   +-----------------+-----------------------+-------------------------+
   | 2001            | Synch-NoReady         | The data to be          |
   |                 |                       | smoothed is not         |
   |                 |                       | ready.                  |
   +-----------------+-----------------------+-------------------------+
   | 2002            | Synch-Unsupport       | The request for         |
   |                 |                       | smooth data is not      |
   |                 |                       | supported.              |
   +-----------------+-----------------------+-------------------------+
   | 2003-2999       | Unassigned            | Unassigned data         |
   |                 |                       | synchronization         |
   |                 |                       | error codes.            |
   +-----------------+-----------------------+-------------------------+
   | 3000            | Reserved              |                         |
   +-----------------+-----------------------+-------------------------+
   | 3001            | Pool-Mismatch         | The corresponding       |
   |                 |                       | address pool cannot     |
   |                 |                       | be found.               |
   +-----------------+-----------------------+-------------------------+
   | 3002            | Pool-Full             | The address pool is     |
   |                 |                       | fully allocated, and    |
   |                 |                       | no address segment      |
   |                 |                       | is available.           |
   +-----------------+-----------------------+-------------------------+
   | 3003            | Subnet-Mismatch       | The address pool        |
   |                 |                       | subnet cannot be        |
   |                 |                       | found.                  |
   +-----------------+-----------------------+-------------------------+
   | 3004            | Subnet-Conflict       | Subnets in the          |
   |                 |                       | address pool have       |
   |                 |                       | been classified into    |
   |                 |                       | other clients.          |
   +-----------------+-----------------------+-------------------------+
   | 3005-3999       | Unassigned            | Unassigned error        |
   |                 |                       | codes for address       |
   |                 |                       | allocation.             |
   +-----------------+-----------------------+-------------------------+
   | 4000            | Reserved              |                         |
   +-----------------+-----------------------+-------------------------+
   | 4001            | Update-Fail-No-Res    | The forwarding table    |
   |                 |                       | fails to be             |
   |                 |                       | delivered because       |
   |                 |                       | the forwarding          |
   |                 |                       | resources are           |
   |                 |                       | insufficient.           |
   +-----------------+-----------------------+-------------------------+
   | 4002            | QoS-Update-Success    | The QoS policy takes    |
   |                 |                       | effect.                 |
   +-----------------+-----------------------+-------------------------+
   | 4003            | QoS-Update-Sq-Fail    | Failed to process       |
   |                 |                       | the queue in the QoS    |
   |                 |                       | policy.                 |
   +-----------------+-----------------------+-------------------------+
   | 4004            | QoS-Update-CAR-Fail   | Processing of the       |
   |                 |                       | CAR in the QoS          |
   |                 |                       | policy fails.           |
   +-----------------+-----------------------+-------------------------+
   | 4005            | Statistic-Fail-No-Res | Statistics              |
   |                 |                       | processing failed       |
   |                 |                       | due to insufficient     |
   |                 |                       | statistics              |
   |                 |                       | resources.              |
   +-----------------+-----------------------+-------------------------+
   | 4006-4999       | Unassigned            | Unassigned              |
   |                 |                       | forwarding table        |
   |                 |                       | delivery error          |
   |                 |                       | codes.                  |
   +-----------------+-----------------------+-------------------------+
   | 5000-4294967295 | Reserved              |                         |
   +-----------------+-----------------------+-------------------------+

                            Table 9: Error Codes

8.6.  If-Type Values

   Defined values of the If-Type field in the If-Desc sub-TLV (see
   Section 7.3.4) are as follows:

                      +-------+--------------------+
                      | Value | Meaning            |
                      +=======+====================+
                      | 0     | Reserved           |
                      +-------+--------------------+
                      | 1     | Fast Ethernet (FE) |
                      +-------+--------------------+
                      | 2     | GE                 |
                      +-------+--------------------+
                      | 3     | 10GE               |
                      +-------+--------------------+
                      | 4     | 100GE              |
                      +-------+--------------------+
                      | 5     | Eth-Trunk          |
                      +-------+--------------------+
                      | 6     | Tunnel             |
                      +-------+--------------------+
                      | 7     | VE                 |
                      +-------+--------------------+
                      | 8-254 | Unassigned         |
                      +-------+--------------------+
                      | 255   | Reserved           |
                      +-------+--------------------+

                         Table 10: If-Type Values

8.7.  Access-Mode Values

   Defined values of the Access-Mode field in the BAS Function TLV (see
   Section 7.7) are as follows:

                      +-------+---------------------+
                      | Value | Meaning             |
                      +=======+=====================+
                      | 0     | Layer 2 subscriber  |
                      +-------+---------------------+
                      | 1     | Layer 3 subscriber  |
                      +-------+---------------------+
                      | 2     | Layer 2 leased line |
                      +-------+---------------------+
                      | 3     | Layer 3 leased line |
                      +-------+---------------------+
                      | 4-254 | Unassigned          |
                      +-------+---------------------+
                      | 255   | Reserved            |
                      +-------+---------------------+

                        Table 11: Access-Mode Values

8.8.  Access Method Bits

   Defined values of the Auth-Method4 and Auth-Method6 fields in the BAS
   Function TLV (see Section 7.7) are defined as bit fields as follows:

                    +------+-------------------------+
                    | Bit  | Meaning                 |
                    +======+=========================+
                    | 0x01 | PPPoE authentication    |
                    +------+-------------------------+
                    | 0x02 | DOT1X authentication    |
                    +------+-------------------------+
                    | 0x04 | Web authentication      |
                    +------+-------------------------+
                    | 0x08 | Web fast authentication |
                    +------+-------------------------+
                    | 0x10 | Binding authentication  |
                    +------+-------------------------+
                    | 0x20 | Reserved                |
                    +------+-------------------------+
                    | 0x40 | Reserved                |
                    +------+-------------------------+
                    | 0x80 | Reserved                |
                    +------+-------------------------+

                      Table 12: Auth-Method4 Values

                    +------+-------------------------+
                    | Bit  | Meaning                 |
                    +======+=========================+
                    | 0x01 | PPPoE authentication    |
                    +------+-------------------------+
                    | 0x02 | DOT1X authentication    |
                    +------+-------------------------+
                    | 0x04 | Web authentication      |
                    +------+-------------------------+
                    | 0x08 | Web fast authentication |
                    +------+-------------------------+
                    | 0x10 | Binding authentication  |
                    +------+-------------------------+
                    | 0x20 | Reserved                |
                    +------+-------------------------+
                    | 0x40 | Reserved                |
                    +------+-------------------------+
                    | 0x80 | Reserved                |
                    +------+-------------------------+

                      Table 13: Auth-Method6 Values

8.9.  Route-Type Values

   Values of the Route-Type field in the IPv4 and IPv6 Routing TLVs (see
   Sections 7.8.1 and 7.8.2) defined in this document are as follows:

               +---------+---------------------------------+
               | Value   | Meaning                         |
               +=========+=================================+
               | 0       | User host route                 |
               +---------+---------------------------------+
               | 1       | Radius authorization FrameRoute |
               +---------+---------------------------------+
               | 2       | Network segment route           |
               +---------+---------------------------------+
               | 3       | Gateway route                   |
               +---------+---------------------------------+
               | 4       | Radius authorized IP route      |
               +---------+---------------------------------+
               | 5       | L2TP LNS side user route        |
               +---------+---------------------------------+
               | 6-65534 | Unassigned                      |
               +---------+---------------------------------+
               | 65535   | Reserved                        |
               +---------+---------------------------------+

                        Table 14: Route-Type Values

8.10.  Access-Type Values

   Values of the Access-Type field in the Basic Subscriber TLV (see
   Section 7.9.1) defined in this document are as follows:

   +--------+---------------------------------------------------------+
   | Value  | Meaning                                                 |
   +========+=========================================================+
   | 0      | Reserved                                                |
   +--------+---------------------------------------------------------+
   | 1      | PPP access (PPP [RFC1661])                              |
   +--------+---------------------------------------------------------+
   | 2      | PPP over Ethernet over ATM access (PPPoEoA)             |
   +--------+---------------------------------------------------------+
   | 3      | PPP over ATM access (PPPoA [RFC3336])                   |
   +--------+---------------------------------------------------------+
   | 4      | PPP over Ethernet access (PPPoE [RFC2516])              |
   +--------+---------------------------------------------------------+
   | 5      | PPPoE over VLAN access (PPPoEoVLAN [RFC2516])           |
   +--------+---------------------------------------------------------+
   | 6      | PPP over LNS access (PPPoLNS)                           |
   +--------+---------------------------------------------------------+
   | 7      | IP over Ethernet DHCP access (IPoE_DHCP)                |
   +--------+---------------------------------------------------------+
   | 8      | IP over Ethernet EAP authentication access (IPoE_EAP)   |
   +--------+---------------------------------------------------------+
   | 9      | IP over Ethernet Layer 3 access (IPoE_L3)               |
   +--------+---------------------------------------------------------+
   | 10     | IP over Ethernet Layer 2 Static access (IPoE_L2_STATIC) |
   +--------+---------------------------------------------------------+
   | 11     | Layer 2 Leased Line access (L2_Leased_Line)             |
   +--------+---------------------------------------------------------+
   | 12     | Layer 2 VPN Leased Line access (L2VPN_Leased_Line)      |
   +--------+---------------------------------------------------------+
   | 13     | Layer 3 Leased Line access (L3_Leased_Line)             |
   +--------+---------------------------------------------------------+
   | 14     | Layer 2 Leased line Sub-User access                     |
   |        | (L2_Leased_Line_SUB_USER)                               |
   +--------+---------------------------------------------------------+
   | 15     | L2TP LAC tunnel access (L2TP_LAC)                       |
   +--------+---------------------------------------------------------+
   | 16     | L2TP LNS tunnel access (L2TP_LNS)                       |
   +--------+---------------------------------------------------------+
   | 17-254 | Unassigned                                              |
   +--------+---------------------------------------------------------+
   | 255    | Reserved                                                |
   +--------+---------------------------------------------------------+

                       Table 15: Access-Type Values

9.  IANA Considerations

   This document has no IANA actions.

10.  Security Considerations

   The Service, Control, and Management Interfaces between the CP and UP
   might be across the general Internet or other hostile environment.
   The ability of an adversary to block or corrupt messages or introduce
   spurious messages on any one or more of these interfaces would give
   the adversary the ability to stop subscribers from accessing network
   services, disrupt existing subscriber sessions, divert traffic, mess
   up accounting statistics, and generally cause havoc.  Damage would
   not necessarily be limited to one or a few subscribers but could
   disrupt routing or deny service to one or more instances of the CP or
   otherwise cause extensive interference.  If the adversary knows the
   details of the UP equipment and its forwarding rule capabilities, the
   adversary may be able to cause a copy of most or all user data to be
   sent to an address of the adversary's choosing, thus enabling
   eavesdropping.

   Thus, appropriate protections MUST be implemented to provide
   integrity, authenticity, and secrecy of traffic over those
   interfaces.  Whether such protection is used is the decision of the
   network operator.  See [RFC6241] for Mi/NETCONF security.  Security
   on the Si is dependent on the tunneling protocol used, which is out
   of scope for this document.  Security for the Ci, over which S-CUSP
   flows, is further discussed below.

   S-CUSP messages do not provide security.  Thus, if these messages are
   exchanged in an environment where security is a concern, that
   security MUST be provided by another protocol such as TLS 1.3
   [RFC8446] or IPsec.  TLS 1.3 is the mandatory-to-implement protocol
   for interoperability.  The use of a particular security protocol on
   the Ci is determined by configuration.  Such security protocols need
   not always be used, and lesser security precautions might be
   appropriate because, in some cases, the communication between the CP
   and UP is in a benign environment.

11.  References

11.1.  Normative References

   [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/info/rfc20>.

   [RFC793]   Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2661]  Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
              G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
              RFC 2661, DOI 10.17487/RFC2661, August 1999,
              <https://www.rfc-editor.org/info/rfc2661>.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <https://www.rfc-editor.org/info/rfc2865>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

   [802.1Q]   IEEE, "IEEE Standard for Local and metropolitan area
              networks--Bridges and Bridged Networks", IEEE 802.1Q-2018,
              DOI 10.1109/IEEESTD.2018.8403927, July 2018,
              <https://doi.org/10.1109/IEEESTD.2018.8403927>.

   [RFC1661]  Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
              STD 51, RFC 1661, DOI 10.17487/RFC1661, July 1994,
              <https://www.rfc-editor.org/info/rfc1661>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2516]  Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
              and R. Wheeler, "A Method for Transmitting PPP Over
              Ethernet (PPPoE)", RFC 2516, DOI 10.17487/RFC2516,
              February 1999, <https://www.rfc-editor.org/info/rfc2516>.

   [RFC2698]  Heinanen, J. and R. Guerin, "A Two Rate Three Color
              Marker", RFC 2698, DOI 10.17487/RFC2698, September 1999,
              <https://www.rfc-editor.org/info/rfc2698>.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              DOI 10.17487/RFC3022, January 2001,
              <https://www.rfc-editor.org/info/rfc3022>.

   [RFC3336]  Thompson, B., Koren, T., and B. Buffam, "PPP Over
              Asynchronous Transfer Mode Adaptation Layer 2 (AAL2)",
              RFC 3336, DOI 10.17487/RFC3336, December 2002,
              <https://www.rfc-editor.org/info/rfc3336>.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, DOI 10.17487/RFC5511, April
              2009, <https://www.rfc-editor.org/info/rfc5511>.

   [RFC7042]  Eastlake 3rd, D. and J. Abley, "IANA Considerations and
              IETF Protocol and Documentation Usage for IEEE 802
              Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
              October 2013, <https://www.rfc-editor.org/info/rfc7042>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [TR-384]   Broadband Forum, "Cloud Central Office Reference
              Architectural Framework", BBF TR-384, January 2018.

   [WT-459]   Broadband Forum, "Control and User Plane Separation for a
              Disaggregated BNG", BBF WT-459, 2019.

Acknowledgements

   The helpful comments and suggestions from the following individuals
   are hereby acknowledged:

   *  Loa Andersson

   *  Greg Mirsky

Contributors

   Zhenqiang Li
   China Mobile
   32 Xuanwumen West Ave
   Xicheng District
   Beijing
   100053
   China

   Email: lizhenqiang@chinamobile.com


   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Bldg., No. 156 Beiqing Road
   Beijing
   100095
   China

   Email: mach.chen@huawei.com


   Zhouyi Yu
   Huawei Technologies

   Email: yuzhouyi@huawei.com


   Chengguang Niu
   Huawei Technologies

   Email: chengguang.niu@huawei.com


   Zitao Wang
   Huawei Technologies

   Email: wangzitao@huawei.com


   Jun Song
   Huawei Technologies

   Email: song.jun@huawei.com


   Dan Meng
   H3C Technologies
   No. 1 Lixing Center
   No. 8 Guangxun South Street
   Chaoyang District
   Beijing
   100102
   China

   Email: mengdan@h3c.com


   Hanlei Liu
   H3C Technologies
   No. 1 Lixing Center
   No. 8 Guangxun South Street
   Chaoyang District
   Beijing
   100102
   China

   Email: hanlei_liu@h3c.com


   Victor Lopez
   Telefonica
   Spain

   Email: victor.lopezalvarez@telefonica.com


Authors' Addresses

   Shujun Hu
   China Mobile
   32 Xuanwumen West Ave
   Xicheng District
   Beijing
   100053
   China

   Email: hushujun@chinamobile.com


   Donald Eastlake 3rd
   Futurewei Technologies
   2386 Panoramic Circle
   Apopka, FL 32703
   United States of America

   Phone: +1-508-333-2270
   Email: d3e3e3@gmail.com


   Fengwei Qin
   China Mobile
   32 Xuanwumen West Ave
   Xicheng District
   Beijing
   100053
   China

   Email: qinfengwei@chinamobile.com


   Tee Mong Chua
   Singapore Telecommunications Limited
   31 Exeter Road, #05-04 Comcentre Podium Block
   SINGAPORE 239732
   Singapore

   Email: teemong@singtel.com


   Daniel Huang
   ZTE

   Email: huang.guangping@zte.com.cn