doc: Add RFC documents

1 files changed, 723 insertions, 0 deletions

diff --git a/doc/rfc/rfc9105.txt b/doc/rfc/rfc9105.txt
new file mode 100644
index 0000000..4ed81e8
--- /dev/null
+++ b/doc/rfc/rfc9105.txt
@@ -0,0 +1,723 @@
+
+
+
+
+Internet Engineering Task Force (IETF)                        B. Wu, Ed.
+Request for Comments: 9105                                      G. Zheng
+Category: Standards Track                                   M. Wang, Ed.
+ISSN: 2070-1721                                                   Huawei
+                                                             August 2021
+
+
+ A YANG Data Model for Terminal Access Controller Access-Control System
+                             Plus (TACACS+)
+
+Abstract
+
+   This document defines a Terminal Access Controller Access-Control
+   System Plus (TACACS+) client YANG module that augments the System
+   Management data model, defined in RFC 7317, to allow devices to make
+   use of TACACS+ servers for centralized Authentication, Authorization,
+   and Accounting (AAA).  Though being a standard module, this module
+   does not endorse the security mechanisms of the TACACS+ protocol (RFC
+   8907), and TACACS+ MUST be used within a secure deployment.
+
+   The YANG module in this document conforms to the Network Management
+   Datastore Architecture (NMDA) defined in RFC 8342.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in 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/rfc9105.
+
+Copyright Notice
+
+   Copyright (c) 2021 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (https://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+Table of Contents
+
+   1.  Introduction
+   2.  Conventions Used in This Document
+     2.1.  Tree Diagrams
+   3.  Design of the TACACS+ Data Model
+   4.  TACACS+ Client Module
+   5.  Security Considerations
+   6.  IANA Considerations
+   7.  References
+     7.1.  Normative References
+     7.2.  Informative References
+   Appendix A.  Example TACACS+ Authentication Configuration
+   Acknowledgments
+   Authors' Addresses
+
+1.  Introduction
+
+   This document defines a YANG module that augments the System
+   Management data model defined in [RFC7317] to support the
+   configuration and management of TACACS+ clients.
+
+   TACACS+ [RFC8907] provides device administration for routers, network
+   access servers, and other networked devices via one or more
+   centralized servers.
+
+   The System Management data model [RFC7317] defines separate
+   functionality to support local and RADIUS authentication:
+
+   User Authentication Model:  Defines a list of usernames with
+      associated passwords and a configuration leaf to decide the order
+      in which local or RADIUS authentication is used.
+
+   RADIUS Client Model:  Defines a list of RADIUS servers used by a
+      device for centralized user authentication.
+
+   The System Management data model is augmented with the TACACS+ YANG
+   module defined in this document to allow the use of TACACS+ servers
+   as an alternative to RADIUS servers.
+
+   The YANG module can be used with network management protocols such as
+   the Network Configuration Protocol (NETCONF) [RFC6241].
+
+   The YANG module in this document conforms to the Network Management
+   Datastore Architecture (NMDA) defined in [RFC8342].
+
+2.  Conventions Used in This Document
+
+   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.
+
+   The following terms are defined in [RFC6241] and are used in this
+   specification:
+
+   *  configuration data
+
+   *  state data
+
+   The following terms are defined in [RFC7950] and are used in this
+   specification:
+
+   *  augment
+
+   *  data model
+
+   *  data node
+
+   The terminology for describing YANG data models is found in
+   [RFC7950].
+
+2.1.  Tree Diagrams
+
+   The tree diagram used in this document follows the notation defined
+   in [RFC8340].
+
+3.  Design of the TACACS+ Data Model
+
+   This module is used to configure a TACACS+ client on a device to
+   support deployment scenarios with centralized authentication,
+   authorization, and accounting servers.  Authentication is used to
+   validate a user's username and password, authorization allows the
+   user to access and execute commands at various privilege levels
+   assigned to the user, and accounting keeps track of the activity of a
+   user who has accessed the device.
+
+   The ietf-system-tacacs-plus module augments the "/sys:system" path
+   defined in the ietf-system module with the contents of the "tacacs-
+   plus" grouping.  Therefore, a device can use local, RADIUS, or
+   TACACS+ authentication to validate users who attempt to access the
+   router by several mechanisms, e.g., a command line interface or a
+   web-based user interface.
+
+   The "server" list, which is directly under the "tacacs-plus"
+   container, holds a list of TACACS+ servers and uses server-type to
+   distinguish between Authentication, Authorization, and Accounting
+   (AAA) services.  The list of servers is for redundancy.
+
+   Most of the parameters in the "server" list are taken directly from
+   the TACACS+ protocol [RFC8907], and some are derived from the various
+   implementations by network equipment manufacturers.  For example,
+   when there are multiple interfaces connected to the TACACS+ client or
+   server, the source address of outgoing TACACS+ packets could be
+   specified, or the source address could be specified through the
+   interface IP address setting or derived from the outbound interface
+   from the local Forwarding Information Base (FIB).  For the TACACS+
+   server located in a Virtual Private Network (VPN), a VPN Routing and
+   Forwarding (VRF) instance needs to be specified.
+
+   The "statistics" container under the "server list" is a collection of
+   read-only counters for sent and received messages from a configured
+   server.
+
+   The YANG module for TACACS+ client has the following structure:
+
+   module: ietf-system-tacacs-plus
+     augment /sys:system:
+       +--rw tacacs-plus
+          +--rw server* [name]
+             +--rw name                      string
+             +--rw server-type               tacacs-plus-server-type
+             +--rw address                   inet:host
+             +--rw port?                     inet:port-number
+             +--rw (security)
+             |  +--:(obfuscation)
+             |     +--rw shared-secret?      string
+             +--rw (source-type)?
+             |  +--:(source-ip)
+             |  |  +--rw source-ip?          inet:ip-address
+             |  +--:(source-interface)
+             |     +--rw source-interface?   if:interface-ref
+             +--rw vrf-instance?
+             |       -> /ni:network-instances/network-instance/name
+             +--rw single-connection?        boolean
+             +--rw timeout?                  uint16
+             +--ro statistics
+                +--ro connection-opens?      yang:counter64
+                +--ro connection-closes?     yang:counter64
+                +--ro connection-aborts?     yang:counter64
+                +--ro connection-failures?   yang:counter64
+                +--ro connection-timeouts?   yang:counter64
+                +--ro messages-sent?         yang:counter64
+                +--ro messages-received?     yang:counter64
+                +--ro errors-received?       yang:counter64
+                +--ro sessions?              yang:counter64
+
+4.  TACACS+ Client Module
+
+   This YANG module imports typedefs from [RFC6991].  This module also
+   uses the interface typedef from [RFC8343], the leafref to VRF
+   instance from [RFC8529], and the "default-deny-all" extension
+   statement from [RFC8341].
+
+   <CODE BEGINS> file "ietf-system-tacacs-plus@2021-08-05.yang"
+   module ietf-system-tacacs-plus {
+     yang-version 1.1;
+     namespace "urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus";
+     prefix sys-tcs-plus;
+
+     import ietf-inet-types {
+       prefix inet;
+       reference
+         "RFC 6991: Common YANG Data Types";
+     }
+     import ietf-yang-types {
+       prefix yang;
+       reference
+         "RFC 6991: Common YANG Data Types";
+     }
+     import ietf-network-instance {
+       prefix ni;
+       reference
+         "RFC 8529: YANG Data Model for Network Instances";
+     }
+     import ietf-interfaces {
+       prefix if;
+       reference
+         "RFC 8343: A YANG Data Model for Interface Management";
+     }
+     import ietf-system {
+       prefix sys;
+       reference
+         "RFC 7317: A YANG Data Model for System Management";
+     }
+     import ietf-netconf-acm {
+       prefix nacm;
+       reference
+         "RFC 8341: Network Configuration Access Control Model";
+     }
+
+     organization
+       "IETF OPSAWG (Operations and Management Area Working Group)";
+     contact
+       "WG Web:   <http://datatracker.ietf.org/wg/opsawg/>
+        WG List:  <mailto:opsawg@ietf.org>
+
+        Editor: Bo Wu <lana.wubo@huawei.com>
+        Editor: Guangying Zheng <zhengguangying@huawei.com>";
+     description
+       "This module provides configuration of TACACS+ client.
+
+        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 (RFC 2119) (RFC 8174) when, and only when,
+        they appear in all capitals, as shown here.
+
+        Copyright (c) 2021 IETF Trust and the persons identified as
+        authors of the code.  All rights reserved.
+
+        Redistribution and use in source and binary forms, with or
+        without modification, is permitted pursuant to, and subject
+        to the license terms contained in, the Simplified BSD License
+        set forth in Section 4.c of the IETF Trust's Legal Provisions
+        Relating to IETF Documents
+        (https://trustee.ietf.org/license-info).
+
+        This version of this YANG module is part of RFC 9105; see the
+        RFC itself for full legal notices.";
+
+     revision 2021-08-05 {
+       description
+         "Initial revision.";
+       reference
+         "RFC 9105: A YANG Data Model for Terminal Access Controller
+          Access-Control System Plus (TACACS+)";
+     }
+
+     typedef tacacs-plus-server-type {
+       type bits {
+         bit authentication {
+           description
+             "Indicates that the TACACS+ server is providing
+              authentication services.";
+         }
+         bit authorization {
+           description
+             "Indicates that the TACACS+ server is providing
+              authorization services.";
+         }
+         bit accounting {
+           description
+             "Indicates that the TACACS+ server is providing accounting
+              services.";
+         }
+       }
+       description
+         "tacacs-plus-server-type can be set to
+          authentication/authorization/accounting
+          or any combination of the three types.";
+     }
+
+     identity tacacs-plus {
+       base sys:authentication-method;
+       description
+         "Indicates AAA operation using TACACS+.";
+       reference
+         "RFC 8907: The TACACS+ Protocol";
+     }
+
+     grouping statistics {
+       description
+         "Grouping for TACACS+ statistics attributes.";
+       container statistics {
+         config false;
+         description
+           "A collection of server-related statistics objects.";
+         leaf connection-opens {
+           type yang:counter64;
+           description
+             "Number of new connection requests sent to the server,
+              e.g., socket open.";
+         }
+         leaf connection-closes {
+           type yang:counter64;
+           description
+             "Number of connection close requests sent to the server,
+              e.g., socket close.";
+         }
+         leaf connection-aborts {
+           type yang:counter64;
+           description
+             "Number of aborted connections to the server.  These do
+              not include connections that are closed gracefully.";
+         }
+         leaf connection-failures {
+           type yang:counter64;
+           description
+             "Number of connection failures to the server.";
+         }
+         leaf connection-timeouts {
+           type yang:counter64;
+           description
+             "Number of connection timeouts to the server.";
+         }
+         leaf messages-sent {
+           type yang:counter64;
+           description
+             "Number of messages sent to the server.";
+         }
+         leaf messages-received {
+           type yang:counter64;
+           description
+             "Number of messages received from the server.";
+         }
+         leaf errors-received {
+           type yang:counter64;
+           description
+             "Number of error messages received from the server.";
+         }
+         leaf sessions {
+           type yang:counter64;
+           description
+             "Number of TACACS+ sessions completed with the server.
+              If the Single Connection Mode was NOT enabled, the number
+              of sessions is the same as the number of
+              'connection-closes'.  If the Mode was enabled, a single
+              TCP connection may contain multiple TACACS+ sessions.";
+         }
+       }
+     }
+
+     grouping tacacs-plus {
+       description
+         "Grouping for TACACS+ attributes.";
+       container tacacs-plus {
+         must "not(derived-from-or-self(../sys:authentication"
+            + "/sys:user-authentication-order, 'tacacs-plus'))"
+            + " or bit-is-set(server/server-type,'authentication')" {
+           error-message "When 'tacacs-plus' is used as a system"
+                       + " authentication method, a TACACS+"
+                       + " authentication server must be configured.";
+           description
+             "When 'tacacs-plus' is used as an authentication method,
+              a TACACS+ server must be configured.";
+         }
+         description
+           "Container for TACACS+ configurations and operations.";
+         list server {
+           key "name";
+           ordered-by user;
+           description
+             "List of TACACS+ servers used by the device.";
+           leaf name {
+             type string;
+             description
+               "An arbitrary name for the TACACS+ server.";
+           }
+           leaf server-type {
+             type tacacs-plus-server-type;
+             mandatory true;
+             description
+               "Server type: authentication/authorization/accounting and
+                various combinations.";
+           }
+           leaf address {
+             type inet:host;
+             mandatory true;
+             description
+               "The address of the TACACS+ server.";
+           }
+           leaf port {
+             type inet:port-number;
+             default "49";
+             description
+               "The port number of TACACS+ Server port.";
+           }
+           choice security {
+             mandatory true;
+             description
+               "Security mechanism between TACACS+ client and server.
+                This is modeled as a YANG 'choice' so that it can be
+                augmented by a YANG module in a backwards-compatible
+                manner.";
+             case obfuscation {
+               leaf shared-secret {
+                 type string {
+                   length "1..max";
+                 }
+                 nacm:default-deny-all;
+                 description
+                   "The shared secret, which is known to both the
+                    TACACS+ client and server.  TACACS+ server
+                    administrators SHOULD configure a shared secret with
+                    a minimum length of 16 characters.
+                    It is highly recommended that this shared secret is
+                    at least 32 characters long and sufficiently complex
+                    with a mix of different character types,
+                    i.e., upper case, lower case, numeric, and
+                    punctuation.  Note that this security mechanism is
+                    best described as 'obfuscation' and not 'encryption'
+                    as it does not provide any meaningful integrity,
+                    privacy, or replay protection.";
+                 reference
+                   "RFC 8907: The TACACS+ Protocol";
+               }
+             }
+           }
+           choice source-type {
+             description
+               "The source address type for outbound TACACS+ packets.";
+             case source-ip {
+               leaf source-ip {
+                 type inet:ip-address;
+                 description
+                   "Specifies source IP address for TACACS+ outbound
+                    packets.";
+               }
+             }
+             case source-interface {
+               leaf source-interface {
+                 type if:interface-ref;
+                 description
+                   "Specifies the interface from which the IP address
+                    is derived for use as the source for the outbound
+                    TACACS+ packet.";
+               }
+             }
+           }
+           leaf vrf-instance {
+             type leafref {
+               path "/ni:network-instances/ni:network-instance/ni:name";
+             }
+             description
+               "Specifies the VPN Routing and Forwarding (VRF) instance
+                to use to communicate with the TACACS+ server.";
+             reference
+               "RFC 8529: YANG Data Model for Network Instances";
+           }
+           leaf single-connection {
+             type boolean;
+             default "false";
+             description
+               "Indicates whether the Single Connection Mode is enabled
+                for the server.  By default, the Single Connection Mode
+                is disabled.";
+           }
+           leaf timeout {
+             type uint16 {
+               range "1..max";
+             }
+             units "seconds";
+             default "5";
+             description
+               "The number of seconds the device will wait for a
+                response from each TACACS+ server before trying with a
+                different server.";
+           }
+           uses statistics;
+         }
+       }
+     }
+
+     augment "/sys:system" {
+       description
+         "Augments the system model with the tacacs-plus model.";
+       uses tacacs-plus;
+     }
+   }
+   <CODE ENDS>
+
+5.  Security Considerations
+
+   The YANG module specified in this document defines a schema for data
+   that is designed to be accessed via network management protocols such
+   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
+   is the secure transport layer, and the mandatory-to-implement secure
+   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
+   is HTTPS, and the mandatory-to-implement secure transport is TLS
+   [RFC8446].
+
+   The Network Configuration Access Control Model (NACM) [RFC8341]
+   provides the means to restrict access for particular NETCONF or
+   RESTCONF users to a preconfigured subset of all available NETCONF or
+   RESTCONF protocol operations and content.
+
+   There are a number of data nodes defined in this YANG module that are
+   writable/creatable/deletable (i.e., config true, which is the
+   default).  These data nodes may be considered sensitive or vulnerable
+   in some network environments.  Write operations (e.g., edit-config)
+   to these data nodes without proper protection can have a negative
+   effect on network operations.  These are the subtrees and data nodes
+   and their sensitivity/vulnerability:
+
+   /system/tacacs-plus/server:  This list contains the data nodes used
+      to control the TACACS+ servers used by the device.  Unauthorized
+      access to this list could enable an attacker to assume complete
+      control over the device by pointing to a compromised TACACS+
+      server, or to modify the counters to hide attacks against the
+      device.
+
+   /system/tacacs-plus/server/shared-secret:  This leaf controls the key
+      known to both the TACACS+ client and server.  Unauthorized access
+      to this leaf could make the device vulnerable to attacks;
+      therefore, it has been restricted using the "default-deny-all"
+      access control defined in [RFC8341].  When setting, it is highly
+      recommended that the leaf is at least 32 characters long and
+      sufficiently complex with a mix of different character types,
+      i.e., upper case, lower case, numeric, and punctuation.
+
+   This document describes the use of TACACS+ for purposes of
+   authentication, authorization, and accounting; it is vulnerable to
+   all of the threats that are present in TACACS+ applications.  For a
+   discussion of such threats, see Section 10 of the TACACS+ protocol
+   [RFC8907].
+
+6.  IANA Considerations
+
+   IANA has registered the following URI in the "ns" subregistry within
+   the "IETF XML Registry" [RFC3688]:
+
+   URI:  urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus
+   Registrant Contact:  The IESG.
+   XML:  N/A, the requested URI is an XML namespace.
+
+   IANA has registered the following YANG module in the "YANG Module
+   Names" registry [RFC7950]:
+
+   Name:  ietf-system-tacacs-plus
+   Maintained by IANA:  N
+   Namespace:  urn:ietf:params:xml:ns:yang:ietf-system-tacacs-plus
+   Prefix:  sys-tcs-plus
+   Reference:  RFC 9105
+
+7.  References
+
+7.1.  Normative References
+
+   [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>.
+
+   [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>.
+
+   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
+              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
+              <https://www.rfc-editor.org/info/rfc6242>.
+
+   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
+              RFC 6991, DOI 10.17487/RFC6991, July 2013,
+              <https://www.rfc-editor.org/info/rfc6991>.
+
+   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
+              System Management", RFC 7317, DOI 10.17487/RFC7317, August
+              2014, <https://www.rfc-editor.org/info/rfc7317>.
+
+   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
+              RFC 7950, DOI 10.17487/RFC7950, August 2016,
+              <https://www.rfc-editor.org/info/rfc7950>.
+
+   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
+              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
+              <https://www.rfc-editor.org/info/rfc8040>.
+
+   [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>.
+
+   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
+              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
+              <https://www.rfc-editor.org/info/rfc8340>.
+
+   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
+              Access Control Model", STD 91, RFC 8341,
+              DOI 10.17487/RFC8341, March 2018,
+              <https://www.rfc-editor.org/info/rfc8341>.
+
+   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
+              and R. Wilton, "Network Management Datastore Architecture
+              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
+              <https://www.rfc-editor.org/info/rfc8342>.
+
+   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
+              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
+              <https://www.rfc-editor.org/info/rfc8343>.
+
+   [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>.
+
+   [RFC8529]  Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
+              Liu, "YANG Data Model for Network Instances", RFC 8529,
+              DOI 10.17487/RFC8529, March 2019,
+              <https://www.rfc-editor.org/info/rfc8529>.
+
+   [RFC8907]  Dahm, T., Ota, A., Medway Gash, D.C., Carrel, D., and L.
+              Grant, "The Terminal Access Controller Access-Control
+              System Plus (TACACS+) Protocol", RFC 8907,
+              DOI 10.17487/RFC8907, September 2020,
+              <https://www.rfc-editor.org/info/rfc8907>.
+
+7.2.  Informative References
+
+   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
+              DOI 10.17487/RFC3688, January 2004,
+              <https://www.rfc-editor.org/info/rfc3688>.
+
+Appendix A.  Example TACACS+ Authentication Configuration
+
+   The following shows an example where a TACACS+ authentication server
+   instance is configured.
+
+      {
+        "ietf-system:system": {
+          "authentication": {
+            "user-authentication-order": [tacacs-plus, local-users]
+          }
+          "tacacs-plus": {
+            "server": [
+              {
+                "name": "tac_plus1",
+                "server-type": "authentication",
+                "address": "192.0.2.2",
+                "shared-secret": "QaEfThUkO198010075460923+h3TbE8n",
+                "source-ip": "192.0.2.12",
+                "timeout": "10"
+              }
+            ]
+          }
+        }
+      }
+
+Acknowledgments
+
+   The authors wish to thank Alex Campbell, John Heasley, Ebben Aries,
+   Alan DeKok, Joe Clarke, Tom Petch, Robert Wilton, and many others for
+   their helpful comments and suggestions.
+
+Authors' Addresses
+
+   Bo Wu (editor)
+   Huawei Technologies, Co., Ltd
+   Yuhua District
+   101 Software Avenue
+   Nanjing
+   Jiangsu, 210012
+   China
+
+   Email: lana.wubo@huawei.com
+
+
+   Guangying Zheng
+   Huawei Technologies, Co., Ltd
+   Yuhua District
+   101 Software Avenue
+   Nanjing
+   Jiangsu, 210012
+   China
+
+   Email: zhengguangying@huawei.com
+
+
+   Michael Wang (editor)
+   Huawei Technologies, Co., Ltd
+   Yuhua District
+   101 Software Avenue
+   Nanjing
+   210012
+   China
+
+   Email: wangzitao@huawei.com