path: root/doc/rfc/rfc7019.txt

Internet Research Task Force (IRTF)                            J. Buford
Request for Comments: 7019                           Avaya Labs Research
Category: Experimental                                   M. Kolberg, Ed.
ISSN: 2070-1721                                   University of Stirling
                                                          September 2013


                 Application-Layer Multicast Extensions
              to REsource LOcation And Discovery (RELOAD)

Abstract

   We define a REsource LOcation And Discovery (RELOAD) Usage for
   Application-Layer Multicast (ALM) as well as a mapping to the RELOAD
   experimental message type to support ALM.  The ALM Usage is intended
   to support a variety of ALM control algorithms in an overlay-
   independent way.  Two example algorithms are defined, based on Scribe
   and P2PCast.

   This document is a product of the Scalable Adaptive Multicast
   Research Group (SAM RG).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Research Task
   Force (IRTF).  The IRTF publishes the results of Internet-related
   research and development activities.  These results might not be
   suitable for deployment.  This RFC represents the consensus of the
   Scalable Adaptive Multicast Research Group of the Internet Research
   Task Force (IRTF).  Documents approved for publication by the IRSG
   are not a candidate for any level of Internet Standard; see Section 2
   of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7019.










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Copyright Notice

   Copyright (c) 2013 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
   (http://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.

Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Language ......................................5
   2. Definitions .....................................................5
      2.1. Overlay Network ............................................5
      2.2. Overlay Multicast ..........................................5
      2.3. Source-Specific Multicast (SSM) ............................6
      2.4. Any-Source Multicast (ASM) .................................6
      2.5. Peer .......................................................6
   3. Assumptions .....................................................6
      3.1. Overlay ....................................................6
      3.2. Overlay Multicast ..........................................7
      3.3. RELOAD .....................................................7
      3.4. NAT ........................................................7
      3.5. Tree Topology ..............................................7
   4. Architecture Extensions to RELOAD ...............................7
   5. RELOAD ALM Usage ................................................9
   6. ALM Tree Control Signaling ......................................9
   7. ALM Messages Mapped to RELOAD ..................................11
      7.1. Introduction ..............................................11
      7.2. Tree Lifecycle Messages ...................................12
           7.2.1. CreateALMTree ......................................12
           7.2.2. CreateALMTreeResponse ..............................13
           7.2.3. Join ...............................................13
           7.2.4. JoinAccept (Join Response) .........................14
           7.2.5. JoinReject (Join Response) .........................15
           7.2.6. JoinConfirm ........................................15
           7.2.7. JoinConfirmResponse ................................16
           7.2.8. JoinDecline ........................................16
           7.2.9. JoinDeclineResponse ................................16
           7.2.10. Leave .............................................17
           7.2.11. LeaveResponse .....................................17
           7.2.12. Reform or Optimize Tree ...........................17
           7.2.13. ReformResponse ....................................18
           7.2.14. Heartbeat .........................................18



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           7.2.15. Heartbeat Response ................................18
           7.2.16. NodeQuery .........................................19
           7.2.17. NodeQueryResponse .................................19
           7.2.18. Push ..............................................21
           7.2.19. PushResponse ......................................22
   8. Scribe Algorithm ...............................................22
      8.1. Overview ..................................................22
      8.2. Create ....................................................23
      8.3. Join ......................................................24
      8.4. Leave .....................................................24
      8.5. JoinConfirm ...............................................24
      8.6. JoinDecline ...............................................24
      8.7. Multicast .................................................24
   9. P2PCast Algorithm ..............................................25
      9.1. Overview ..................................................25
      9.2. Message Mapping ...........................................25
      9.3. Create ....................................................26
      9.4. Join ......................................................26
      9.5. Leave .....................................................28
      9.6. JoinConfirm ...............................................28
      9.7. Multicast .................................................28
   10. Message Format ................................................28
      10.1. ALMHeader Definition .....................................30
      10.2. ALMMessageContents Definition ............................31
      10.3. Response Codes ...........................................31
   11. Examples ......................................................32
      11.1. Create Tree ..............................................32
      11.2. Join Tree ................................................33
      11.3. Leave Tree ...............................................35
      11.4. Push Data ................................................35
   12. Kind Definitions ..............................................36
      12.1. ALMTree Kind Definition ..................................36
   13. RELOAD Configuration File Extensions ..........................37
   14. IANA Considerations ...........................................37
      14.1. ALM Algorithm Types ......................................37
      14.2. Message Code Registration ................................38
      14.3. Error Code Registration ..................................38
   15. Security Considerations .......................................39
   16. Acknowledgements ..............................................40
   17. References ....................................................40
      17.1. Normative Reference ......................................40
      17.2. Informative References ...................................40









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1.  Introduction

   The concept of scalable adaptive multicast includes both scaling
   properties and adaptability properties.  Scalability is intended to
   cover:

   o  large group size

   o  large numbers of small groups

   o  rate of group membership change

   o  admission control for QoS

   o  use with network-layer QoS mechanisms

   o  varying degrees of reliability

   o  trees connecting nodes over the global Internet

   Adaptability includes

   o  use of different control mechanisms for different multicast trees
      depending on initial application parameters or application classes

   o  changing multicast tree structure depending on changes in
      application requirements, network conditions, and membership

   Application-Layer Multicast (ALM) has been demonstrated to be a
   viable multicast technology where native multicast isn't available.
   Many ALM designs have been proposed.  This ALM Usage focuses on:

   o  ALM implemented in RELOAD-based overlays

   o  Support for a variety of ALM control algorithms

   o  Providing a basis for defining a separate hybrid ALM RELOAD Usage

   RELOAD [RELOAD] has an application extension mechanism in which a new
   type of application defines a Usage.  A RELOAD Usage defines a set of
   data types and rules for their use.  In addition, this document
   describes additional message types and a new ALM algorithm plugin
   architectural component.

   This document represents the consensus of the SAM RG.  It was
   repeatedly discussed within the research group, as well as with other
   Application-Layer Multicast experts.




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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Definitions

   We adopt the terminology defined in Section 3 of [RELOAD],
   specifically the distinction between "node", "peer", and "client".

2.1.  Overlay Network

   Overlay network: An application-layer virtual or logical network with
   addressable end points that provides connectivity, routing, and
   messaging between end points.  Overlay networks are frequently used
   as a substrate for deploying new network services or for providing a
   routing topology not available from the underlying physical network.
   Many peer-to-peer systems are overlay networks that run on top of the
   Internet.  In Figure 1, "P" indicates overlay peers, and peers are
   connected in a logical address space.  The links shown in the figure
   represent predecessor/successor links.  Depending on the overlay
   routing model, additional or different links may be present.

                           P    P    P   P     P
                         ..+....+....+...+.....+...
                        .                          +P
                      P+                            .
                        .                          +P
                         ..+....+....+...+.....+...
                           P    P    P   P     P

                     Figure 1: Overlay Network Example

2.2.  Overlay Multicast

   Overlay Multicast (OM): Hosts participating in a multicast session
   form an overlay network and utilize unicast connections among pairs
   of hosts for data dissemination [BUFORD2009] [KOLBERG2010]
   [BUFORD2008].  The hosts in overlay multicast exclusively handle
   group management, routing, and tree construction, without any support
   from Internet routers.  This is also commonly known as Application-
   Layer Multicast (ALM) or End-System Multicast (ESM).  We call systems
   that use proxies connected in an overlay multicast backbone "proxied
   overlay multicast" or POM.






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2.3.  Source-Specific Multicast (SSM)

   SSM tree: The creator of the tree is the source.  It sends data
   messages to the tree root that are forwarded down the tree.

2.4.  Any-Source Multicast (ASM)

   ASM tree: A node sending a data message sends the message to its
   parent and its children.  Each node receiving a data message from one
   edge forwards it to the remaining tree edges to which it is
   connected.

2.5.  Peer

   Peer: An autonomous end system that is connected to the physical
   network and participates in and contributes resources to overlay
   construction, routing, and maintenance.  Some peers may also perform
   additional roles such as connection relays, super nodes, NAT
   traversal assistance, and data storage.

3.  Assumptions

3.1.  Overlay

   Peers connect in a large-scale overlay, which may be used for a
   variety of peer-to-peer applications in addition to multicast
   sessions.  Peers may assume additional roles in the overlay beyond
   participation in the overlay and in multicast trees.  We assume a
   single-structured overlay routing algorithm is used.  Any of a
   variety of multi-hop, one-hop, or variable-hop overlay algorithms
   could be used.

   Castro, et al. [CASTRO2003] compared multi-hop overlays and found
   that tree-based construction in a single overlay outperformed using
   separate overlays for each multicast session.  We use a single
   overlay rather than separate overlays per multicast session.

   An overlay multicast algorithm may leverage the overlay's mechanism
   for maintaining overlay state in the face of churn.  For example, a
   peer may store a number of DHT (Distributed Hash Table) entries.
   When the peer gracefully leaves the overlay, it transfers those
   entries to the nearest peer.  When another peer joins that is closer
   to some of the entries than the current peer that holds those
   entries, than those entries are migrated.  Overlay churn affects
   multicast trees as well; remedies include automatic migration of the
   tree state and automatic rejoin operations for dislocated child
   nodes.




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3.2.  Overlay Multicast

   The overlay supports concurrent multiple multicast trees.  The limit
   on the number of concurrent trees depends on peer and network
   resources and is not an intrinsic property of the overlay.

3.3.  RELOAD

   We use RELOAD [RELOAD] as the peer-to-peer (P2P) overlay for data
   storage and the mechanism by which the peers interconnect and route
   messages.  RELOAD is a generic P2P overlay, and application support
   is defined by profiles called Usages.

3.4.  NAT

   Some nodes in the overlay may be in a private address space and
   behind firewalls.  We use the RELOAD mechanisms for NAT traversal.
   We permit clients to be leaf nodes in an ALM tree.

3.5.  Tree Topology

   All tree control messages are routed in the overlay.  Two types of
   data or media topologies are envisioned: 1) tree edges are paths in
   the overlay, and 2) tree edges are direct connections between a
   parent and child peer in the tree, formed using the RELOAD AppAttach
   method.

4.  Architecture Extensions to RELOAD

   There are two changes as depicted in Figure 2.  New ALM messages are
   mapped to RELOAD Message Transport using the RELOAD experimental
   message type.  A plugin for ALM algorithms handles the ALM state and
   control.  The ALM algorithm is under control of the application via
   the Group API [COMMON-API].

















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                                                       +---------+
                                                       |Group API|
                                                       +---------+
                                                            |
          ------------------- Application  ------------------------
              +-------+                                     |
              | ALM   |                                     |
              | Usage |                                     |
              +-------+                                     |
           -------------- Messaging Service Boundary --------------
                                                            |
             +--------+      +-----------+---------+    +---------+
             | Storage|<---> | RELOAD    | ALM     |<-->| ALM Alg |
             +--------+      | Message   | Messages|    +---------+
                     ^       | Transport |         |
                     |       +-----------+---------+
                     v          |    |
                    +-------------+  |
                    | Topology    |  |
                    | Plugin      |  |
                    +-------------+  |
                       ^             |
                       v             v
                    +-------------------+
                    | Forwarding &      |
                    | Link Management   |
                    +-------------------+

           ---------- Overlay Link Service Boundary --------------

                 Figure 2: RELOAD Architecture Extensions

   The ALM components interact with RELOAD as follows:

   o  ALM uses the RELOAD data storage functionality to store an ALMTree
      instance when a new ALM tree is created in the overlay and to
      retrieve ALMTree instance(s) for existing ALM trees.

   o  ALM applications and management tools may use the RELOAD data
      storage functionality to store diagnostic information about the
      operation of trees, including average number of trees, delay from
      source to leaf nodes, bandwidth use, and packet loss rate.  In
      addition, diagnostic information may include statistics specific
      to the tree root or to any node in the tree.







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5.  RELOAD ALM Usage

   Applications of RELOAD are restricted in the data types that can be
   stored in the DHT.  The profile of accepted data types for an
   application is referred to as a Usage.  RELOAD is designed so that
   new applications can easily define new Usages.  New RELOAD Usages are
   needed for multicast applications since the data types in base RELOAD
   and existing Usages are not sufficient.

   We define an ALM Usage in RELOAD.  This ALM Usage is sufficient for
   applications that require ALM functionality in the overlay.  Figure 2
   shows the internal structure of the ALM Usage.  This contains the
   Group API ([COMMON-API]), an ALM algorithm plugin (e.g., Scribe), and
   the ALM messages that are then sent out to the RELOAD network.

   A RELOAD Usage is required [RELOAD] to define the following:

   o  Kind-ID and code points

   o  data structures for each Kind

   o  access control rules for each Kind

   o  the Resource Name used to hash to the Resource ID that determines
      where the Kind is stored

   o  address restoration after recovery from a network partition (to
      form a single coherent network)

   o  the types of connections that can be initiated using AppConnect

   An ALM group_id is a RELOAD node_id.  The owner of an ALM group
   creates a RELOAD node_id as specified in [RELOAD].  This means that a
   group_id is used as a RELOAD Destination for overlay routing
   purposes.

6.  ALM Tree Control Signaling

   Peers use the overlay to support ALM operations such as:

   o  CreateALMTree

   o  Join

   o  Leave

   o  Reform or optimize tree




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   There are a variety of algorithms for peers to form multicast trees
   in the overlay.  The approach presented here permits multiple such
   algorithms to be supported in the overlay since different algorithms
   may be more suitable for certain application requirements; the
   approach also supports experimentation.  Therefore, overlay messaging
   corresponding to the set of overlay multicast operations MUST carry
   algorithm identification information.

   For example, for small groups, the join point might be directly
   assigned by the rendezvous point, while for large trees the Join
   request might be propagated down the tree with candidate parents
   forwarding their position directly to the new node.

   Here is a simplistic notation for forming a multicast tree in the
   overlay.  Its main advantage is the use of the overlay for routing
   both control and data messages.  The group creator does not have to
   be the root of the tree or even in the tree.  It does not consider
   per-node load, admission control, or alternative paths.  After the
   creation of a tree, the group_id is expected to be advertised or
   distributed out of band, perhaps by publishing in the DHT.
   Similarly, joining peers will discover the group_id out of band,
   perhaps by a lookup in the tree.

   As stated earlier, multiple algorithms will coexist in the overlay.

   1.  Peer that initiates multicast group:

       group_id = create();  // Allocate a unique group_id.
                             // The root is the nearest
                             // peer in the overlay.

   2.  Any joining peer:

       joinTree(group_id); // sends "join group_id" message

       The overlay routes the Join request using the overlay routing
       mechanism toward the peer with the nearest ID to the group_id.
       This peer is the root.  Peers on the path to the root join the
       tree as forwarding points.

   3.  Leave Tree:

       leaveTree(group_id); // removes this node from the tree








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       Propagates a Leave request to each child node and to the parent
       node.  If the parent node is a forwarding node and this is its
       last child, then it propagates a Leave request to its parent.  A
       child node receiving a Leave request from a parent sends a Join
       request to the group_id.

   4.  Message forwarding:

       multicastMsg(group_id, msg);

       For message forwarding, both Any-Source Multicast (ASM) and
       Source-Specific Multicast (SSM) approaches may be used.

7.  ALM Messages Mapped to RELOAD

7.1.  Introduction

   In this document, we define messages for overlay multicast tree
   creation, using an existing protocol (RELOAD) in the P2P-SIP WG
   [RELOAD] for a universal structured peer-to-peer overlay protocol.
   RELOAD provides the mechanism to support a number of overlay
   topologies.  Hence, the overlay multicast framework defined in this
   document can be used with P2P-SIP and makes the Scalable Adaptive
   Multicast (SAM) framework overlay agnostic.

   As discussed in the SAM requirements document [SAM-GENERIC], there
   are a variety of ALM tree formation and tree maintenance algorithms.
   The intent of this specification is to be algorithm agnostic, similar
   to how RELOAD is overlay algorithm agnostic.  We assume that all
   control messages are propagated using overlay routed messages.

   The message types needed for ALM behavior are divided into the
   following categories:

   o  Tree lifecycle (Create, Join, Leave, Reform, Heartbeat)

   o  Peer region and multicast properties

   The message codes are defined in Section 14.2 of this document.
   Messages are mapped to the RELOAD experimental message type.

   In the following sections, the protocol messages as mapped to RELOAD
   are discussed.  Detailed example message flows are provided in
   Section 11.







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   In the following descriptions, we use the datatype Dictionary, which
   is a set of opaque values indexed by an opaque key with one value for
   each key.  A single dictionary entry is represented by a
   DictionaryEntry as defined in Section 7.2.3 of the RELOAD document
   [RELOAD].  The Dictionary datatype is defined as follows:

   struct {
     DictionaryEntry elements<0..2^16-1>;
     } Dictionary;

7.2.  Tree Lifecycle Messages

   Peers use the overlay to transmit ALM operations defined in this
   section.

7.2.1.  CreateALMTree

   A new ALM tree is created in the overlay with the identity specified
   by group_id.  The common interpretation in a DHT-based overlay of
   group_id is that the peer with a peer_id closest to and less than the
   group_id is the root of the tree.  However, other overlay types are
   supported.  The tree has no children at the time it is created.

   The group_id is generated from a well-known session key to be used by
   other peers to address the multicast tree in the overlay.  The
   generation of the group_id from the session_key MUST be done using
   the overlay's ID-generation mechanism.

      struct {
        node_id peer_id;
        opaque session_key<0..2^32-1>;
        node_id group_id;
        Dictionary options;
      } ALMTree;

   peer_id: overlay address of the peer that creates the multicast tree.

   session_key: a well-known string that when hashed using the overlay's
   ID-generation algorithm produces the group_id.

   group_id: overlay address of the root of the tree.

   options: name-value list of properties to be associated with the
   tree, such as the maximum size of the tree, restrictions on peers
   joining the tree, latency constraints, preference for distributed or
   centralized tree formation and maintenance, and Heartbeat interval.





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   Tree creation is subject to access control since it involves a Store
   operation.  The NODE-MATCH access policy defined in Section 7.3.2 of
   [RELOAD] is used.

   A successful CreateALMTree causes an ALMTree structure to be stored
   in the overlay at the node G responsible for the group_id.  This node
   G performs the RELOAD-defined StoreReq operation as a side effect of
   performing the CreateALMTree.  If the StoreReq fails, the
   CreateALMTree fails too.

   After a successful CreateALMTree, peers can use the RELOAD Fetch
   method to retrieve the ALMTree struct at address group_id.  The
   ALMTree Kind is defined in Section 12.1.

7.2.2.  CreateALMTreeResponse

   After receiving a CreateALMTree message from node S, the peer sends a
   CreateALMTreeResponse to node S.

        struct {
          Dictionary options;
        } CreateALMTreeResponse;

   options: A node may provide algorithm-dependent parameters about the
   created tree to the requesting node.

7.2.3.  Join

   Join causes the distributed algorithm for peer join of a specific ALM
   group to be invoked.  The definition of the Join request is shown
   below.  If successful, the joining peer is notified of one or more
   candidate parent peers in one or more JoinAccept messages.  The
   particular ALM join algorithm is not specified in this protocol.

      struct {
        node_id peer_id;
        node_id group_id;
        Dictionary options;
      } Join;

   peer_id: overlay address of joining/leaving peer

   group_id: overlay address of the root of the tree

   options: name-value list of options proposed by joining peer






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   RELOAD is a request-response protocol.  Consequently, the messages
   JoinAccept and JoinReject (defined below) are matching responses for
   Join.  If JoinReject is received, then no further action on this
   request is carried out.  If JoinAccept is received, then either a
   JoinConfirm or a JoinDecline message (see below) is sent.  The
   matching response for JoinConfirm is JoinConfirmResponse.  The
   matching response for JoinDecline is JoinDeclineResponse.

   The following list shows the matching request-responses according to
   the request-response mechanism defined in [RELOAD].

      Join -- JoinAccept: Node C sends a Join request to node P.  If
      node P accepts, it responds with JoinAccept.

      Join -- JoinReject: Node C sends a Join request to node P.  If
      node P does not accept the Join request, it responds with
      JoinReject.

      JoinConfirm -- JoinConfirmResponse: If node P sent node C a
      JoinAccept and node C confirms with a JoinConfirm request, then
      node P responds with a JoinConfirmResponse.

      JoinDecline -- JoinDeclineResponse: If node P sent node C a
      JoinAccept and node C declines with a JoinDecline request, then
      node P responds with a JoinDeclineResponse.

   Thus, Join, JoinConfirm, and JoinDecline are treated as requests as
   defined in RELOAD, are mapped to the RELOAD exp_a_req message, and
   are therefore retransmitted until either a retry limit is reached or
   a matching response received.  JoinAccept, JoinReject,
   JoinConfirmResponse, and JoinDeclineResponse are treated as message
   responses as defined above and are mapped to the RELOAD exp_a_ans
   message.

   The Join behavior can be described as follows:

   if(checkAccept(msg)) {
       recvJoins.add(msg.source, msg.group_id)
       SEND(JoinAccept(node_id, msg.source, msg.group_id))
   }

7.2.4.  JoinAccept (Join Response)

   JoinAccept tells the requesting joining peer that the indicated peer
   is available to act as its parent in the ALM tree specified by
   group_id, with the corresponding options specified.  A peer MAY
   receive more than one JoinAccept from different candidate parent
   peers in the group_id tree.  The peer accepts a peer as parent using



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   a JoinConfirm message.  A JoinAccept that receives neither a
   JoinConfirm nor JoinDecline message MUST expire.  RELOAD
   implementations are able to read a local configuration file for
   settings.  It is assumed that this file contains the timeout value to
   be used.

      struct {
        node_id parent_peer_id;
        node_id child_peer_id;
        node_id group_id;
        Dictionary options;
      } JoinAccept;

   parent_peer_id: overlay address of a peer that accepts the joining
   peer

   child_peer_id: overlay address of joining peer

   group_id: overlay address of the root of the tree

   options: name-value list of options accepted by parent peer

7.2.5.  JoinReject (Join Response)

   A peer receiving a Join request responds with a JoinReject response
   to indicate the request is rejected.

7.2.6.  JoinConfirm

   A peer receiving a JoinAccept message that it wishes to accept MUST
   explicitly accept it using a JoinConfirm message before the
   expiration of a timer for the JoinAccept message.  The joining peer
   MUST include only those options from the JoinAccept that it also
   accepts, completing the negotiation of options between the two peers.

      struct {
        node_id child_peer_id;
        node_id parent_peer_id;
        node_id group_id;
        Dictionary options;
      } JoinConfirm;

   child_peer_id: overlay address of joining peer that is a child of the
   parent peer

   parent_peer_id: overlay address of the peer that is the parent of the
   joining peer




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   group_id: overlay address of the root of the tree

   options: name-value list of options accepted by both peers

   The JoinConfirm message behavior is described below:

   if(recvJoins.contains(msg.source,msg.group_id)){
      if !(groups.contains(msg.group_id)) {
         groups.add(msg.group_id)
         SEND(msg,msg.group_id)
      }
      groups[msg.group_id].children.add(msg.source)
      recvJoins.del(msg.source, msg.group_id)
   }

7.2.7.  JoinConfirmResponse

   A peer receiving a JoinConfirm message responds with a
   JoinConfirmResponse message.

7.2.8.  JoinDecline

   A peer receiving a JoinAccept message that it does not wish to accept
   MAY explicitly decline it using a JoinDecline message.

      struct {
        node_id peer_id;
        node_id parent_peer_id;
        node_id group_id;
      } JoinDecline;

   peer_id: overlay address of joining peer that declines the JoinAccept

   parent_peer_id: overlay address of the peer that issued a JoinAccept
   to this peer

   group_id: overlay address of the root of the tree

   The behavior of the JoinDecline message is described as follows:

   if(recvJoins.contains(msg.source,msg.group_id))
      recvJoins.del(msg.source, msg.group_id)

7.2.9.  JoinDeclineResponse

   A peer receiving a JoinConfirm message responds with a
   JoinDeclineResponse message.




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7.2.10.  Leave

   A peer that is part of an ALM tree identified by group_id that
   intends to detach from either a child or parent peer SHOULD send a
   Leave request to the peer from which it wishes to detach.  A peer
   receiving a Leave request from a peer that is neither in its parent
   nor child lists SHOULD ignore the message.

      struct {
        node_id peer_id;
        node_id group_id;
        Dictionary options;
      } Leave;

   peer_id: overlay address of leaving peer

   group_id: overlay address of the root of the tree

   options: name-value list of options

   The behavior of the Leave request can be described as:

   groups[msg.group_id].children.remove(msg.source)
   if (groups[msg.group].children = 0)
         SEND(msg,groups[msg.group_id].parent)

7.2.11.  LeaveResponse

   A peer receiving a Leave request responds with a LeaveResponse
   message.

7.2.12.  Reform or Optimize Tree

   This triggers a reorganization of either the entire tree or only a
   subtree.  It MAY include hints to specific peers of recommended
   parent or child peers to which to reconnect.  A peer receiving this
   message MAY ignore it, MAY propagate it to other peers in its
   subtree, and MAY invoke local algorithms for selecting preferred
   parent and/or child peers.

      struct {
        node_id group_id;
        node_id peer_id;
        Dictionary options;
      } Reform;

   group_id: overlay address of the root of the tree




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   peer_id: if omitted, then the tree is reorganized starting from the
   root; otherwise, it is reorganized only at the subtree identified by
   peer_id.

   options: name-value list of options

7.2.13.  ReformResponse

   A peer receiving a Reform message responds with a ReformResponse.

      struct {
        Dictionary options;
      } ReformResponse;

   options: algorithm-dependent information about the results of the
   Reform operation

7.2.14.  Heartbeat

   A child node signals to its adjacent parent nodes in the tree that it
   is alive.  If a parent node does not receive a Heartbeat message
   within N Heartbeat time intervals, it MUST treat this as an explicit
   Leave request from the unresponsive peer.  N is configurable.  RELOAD
   implementations are able to read a local configuration file for
   settings.  It is assumed that this file contains the value for N to
   be used.

      struct {
        node_id peer_id_src;
        node_id peer_id_dst;
        node_id group_id;
        Dictionary options;
      } Heartbeat;

   peer_id_src: source of Heartbeat

   peer_id_dst: destination of Heartbeat

   group_id: overlay address of the root of the tree

   options: an algorithm may use the Heartbeat message to provide state
   information to adjacent nodes in the tree









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7.2.15.  Heartbeat Response

   A parent node responds with a HeartbeatResponse to a Heartbeat from a
   child node indicating that it has received the Heartbeat message.

7.2.16.  NodeQuery

   The NodeQuery message is used to obtain information about the state
   and performance of the tree on a per-node basis.  A set of nodes
   could be queried to construct a centralized view of the multicast
   trees, similar to a web crawler.

        struct {
          node_id peer_id_src;
          node_id peer_id_dst;
        } NodeQuery;

   peer_id_src: source of query

   peer_id_dst: destination of query

7.2.17.  NodeQueryResponse

   The response to a NodeQuery message contains a NodeStatistics
   instance for this node.

   public struct {
      uint32        node_lifetime;
      uint32        total_number_trees;
      uint16        number_algorithms_supported;
      uint8         algorithms_supported[32];
      TreeData      max_tree_data;
      uint16        number_active_trees;
      TreeData      tree_data<0..2^8-1>;
      ImplementationInfo impl_info;
   }  NodeStatistics;

      node_lifetime: time the node has been alive in seconds since last
      restart

      total_number_trees: total number of trees this node has been part
      of during the node lifetime

      number_algorithms_supported: value between 0..2^16-1 corresponding
      to the number of algorithms supported

      algorithms_supported: list of algorithms, each byte encoded using
      the corresponding algorithm code



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      max_tree_data: data about tree with largest number of nodes that
      this node was part of.  NodeQuery can be used to crawl all the
      nodes in an ALM tree to fill this field.  This is intended to
      support monitoring, algorithm design, and general experimentation
      with ALM in RELOAD.

      number_active_trees: current number of trees that the node is part
      of

      tree_data: details of each active tree; the number of such is
      specified by number_active_trees

      impl_info: information about the implementation of this Usage

   public struct {
     uint32       tree_id;
     uint8        algorithm;
     node_id      tree_root;
     uint8        number_parents;
     node_id      parent<0..2^8-1>;
     uint16       number_child_nodes;
     node_id      children<0..2^16-1>;
     uint32       path_length_to_root;
     uint32       path_delay_to_root;
     uint32       path_delay_to_child;
   } TreeData;

      tree_id: the ID of the tree

      algorithm: code identifying the multicast algorithm used by this
      tree

      tree_root: node_id of tree root, or 0 if unknown

      number_parents: 0 .. 2^8-1 indicates number of parent nodes for
      this node

      parent: the RELOAD node_id of each parent node

      number_child_nodes: 0..2^16-1 indicates number of children

      children: the RELOAD node_id of each child node

      path_length_to_root: number of overlay hops to the root of the
      tree

      path_delay_to_root: RTT in milliseconds to root node




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      path_delay_to_child: last measured RTT in milliseconds to child
      node with largest RTT

   public struct {
     uint32       join_confirm_timeout;
     uint32       heartbeat_interval;
     uint32       heartbeat_response_timeout;
     uint16       info_length;
     uint8        info<0..2^16-1>;
   } ImplementationInfo;

      join_confirm_timeout: The default time for
      JoinConfirm/JoinDecline, intended to provide sufficient time for a
      Join request to receive all responses and confirm the best choice.
      Default value is 5000 msec.  An implementation can change this
      value.

      heartbeat_interval: The default Heartbeat interval is 2000 msec.
      Different interoperating implementations could use different
      intervals.

      heartbeat_response_timeout: The default Heartbeat timeout is 5000
      msec and is the max time between Heartbeat reports from an
      adjacent node in the tree at which point the Heartbeat is missed.

      info_length: length of the info field

      info: implementation-specific information, such as name of
      implementation, build version, and implementation-specific
      features





















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7.2.18.  Push

   A peer sends arbitrary multicast data to other peers in the tree.
   Nodes in the tree forward this message to adjacent nodes in the tree
   in an algorithm-dependent way.

      struct {
        node_id group_id;
        uint8  priority;
        uint32 length;
        uint8  data<0..2^32-1>;
      } Push;

   group_id: overlay address of root of the ALM tree

   priority: the relative priority of the message; highest priority is
   255.  A node may ignore this field.

   length: length of the data field in bytes

   data: the data

   In pseudocode, the behavior of Push can be described as:

   foreach(groups[msg.group_id].children as node_id)
        SEND(msg,node_id)
   if memberOf(msg.group_id)
        invokeMessageHandler(msg.group_id, msg)

7.2.19.  PushResponse

   After receiving a Push message from node S, the receiving peer sends
   a PushResponse to node S.

      struct {
        Dictionary options;
      } PushResponse;

   options: A node may provide feedback to the sender about previous
   Push messages in some window, for example, the last N Push messages.
   The feedback could include, for each Push message received, the
   number of adjacent nodes that were forwarded the Push message and the
   number of adjacent nodes from which a PushResponse was received.








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8.  Scribe Algorithm

8.1.  Overview

   Figure 3 shows a mapping between RELOAD ALM messages (as defined in
   Section 5 of this document) and Scribe messages as defined in
   [CASTRO2002].

              +---------+-------------------+-----------------+
              | Section |RELOAD ALM Message | Scribe Message  |
              +---------+-------------------+-----------------+
              | 7.2.1   | CreateALMTree     | Create          |
              +---------+-------------------+-----------------+
              | 7.2.3   | Join              | Join            |
              +---------+-------------------+-----------------+
              | 7.2.4   | JoinAccept        |                 |
              +---------+-------------------+-----------------+
              | 7.2.6   | JoinConfirm       |                 |
              +---------+-------------------+-----------------+
              | 7.2.8   | JoinDecline       |                 |
              +---------+-------------------+-----------------+
              | 7.2.10  | Leave             | Leave           |
              +---------+-------------------+-----------------+
              | 7.2.12  | Reform            |                 |
              +---------+-------------------+-----------------+
              | 7.2.14  | Heartbeat         |                 |
              +---------+-------------------+-----------------+
              | 7.2.16  | NodeQuery         |                 |
              +---------+-------------------+-----------------+
              | 7.2.18  | Push              | Multicast       |
              +---------+-------------------+-----------------+
              |         | Note 1            | deliver         |
              +---------+-------------------+-----------------+
              |         | Note 1            | forward         |
              +---------+-------------------+-----------------+
              |         | Note 1            | route           |
              +---------+-------------------+-----------------+
              |         | Note 1            | send            |
              +---------+-------------------+-----------------+

                   Figure 3: Mapping to Scribe Messages

   Note 1: These Scribe messages are handled by RELOAD messages.

   The following sections describe the Scribe algorithm in more detail.






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8.2.  Create

   This message will create a group with group_id.  This message MUST be
   delivered to the node whose node_id is closest to the group_id.  This
   node becomes the rendezvous point and root for the new multicast
   tree.  Groups MAY have multiple sources of multicast messages.

8.3.  Join

   To join a multicast tree, a node SHOULD send a Join request with the
   group_id as the key.  This message gets routed by the overlay to the
   rendezvous point of the tree.  If an intermediate node is already a
   forwarder for this tree, it SHOULD add the joining node as a child.
   Otherwise, the node SHOULD create a child table for the group and add
   the joining node.  It SHOULD then send the Join request towards the
   rendezvous point terminating the Join request from the child.

   To adapt the Scribe algorithm to the ALM Usage proposed here, after a
   Join request is accepted, a JoinAccept message MUST be returned to
   the joining node.

8.4.  Leave

   When leaving a multicast group, a node SHOULD change its local state
   to indicate that it left the group.  If the node has no children in
   its table, it MUST send a Leave request to its parent, from where it
   SHOULD travel up the multicast tree and stop at a node that still has
   children remaining after removing the leaving node.

8.5.  JoinConfirm

   This message is not part of the Scribe protocol but is required by
   the basic protocol proposed in this document.  Thus, the Usage MUST
   send this message to confirm a joining node accepting its parent
   node.

8.6.  JoinDecline

   Like JoinConfirm, this message is not part of the Scribe protocol.
   Thus, the Usage MUST send this message if a peer receiving a
   JoinAccept message wishes to decline it.

8.7.  Multicast

   A message to be multicast to a group MUST be sent to the rendezvous
   node from where it is forwarded down the tree.  If a node is a member
   of the tree rather than just a forwarder, it SHOULD pass the
   multicast data up to the application.



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9.  P2PCast Algorithm

9.1.  Overview

   P2PCast [P2PCAST] creates a forest of related trees to increase load
   balancing.  P2PCast is independent of the underlying P2P substrate.
   Its goals and approach are similar to SplitStream [SPLITSTREAM]
   (which assumes Pastry as the P2P overlay).  In P2PCast, the content
   provider splits the stream of data into f stripes.  Each tree in the
   forest of multicast trees is an (almost) full tree of arity f.  These
   trees are conceptually separate: every node of the system appears
   once in each tree, with the content provider being the source in all
   of them.  To ensure that each peer contributes as much bandwidth as
   it receives, every node is a leaf in all the trees except for one, in
   which the node will serve as an internal node (proper tree of this
   node).  To reduce the complexity of the discussion that follows, the
   remainder of this section will assume that f = 2.  However, the
   algorithm scales for any number f.

   P2PCast distinguishes the following types of nodes:

   o  Incomplete Node: A node with less than f children in its proper
      stripe

   o  Only-Child Node: A node whose parent (in any multicast tree) is an
      incomplete node

   o  Complete Node: A node with exactly f children in its proper stripe

   o  Special Node: A single node that is a leaf in all multicast trees
      of the forest




















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9.2.  Message Mapping

   Figure 4 shows a mapping between RELOAD ALM messages (as defined in
   Section 5 of this document) and P2PCast messages as defined in
   [P2PCAST].

               +---------+-------------------+-----------------+
               | Section |RELOAD ALM Message | P2PCast Message |
               +---------+-------------------+-----------------+
               | 7.2.1   | CreateALMTree     | Create          |
               +---------+-------------------+-----------------+
               | 7.2.3   | Join              | Join            |
               +---------+-------------------+-----------------+
               | 7.2.4   | JoinAccept        |                 |
               +---------+-------------------+-----------------+
               | 7.2.6   | JoinConfirm       |                 |
               +---------+-------------------+-----------------+
               | 7.2.8   | JoinDecline       |                 |
               +---------+-------------------+-----------------+
               | 7.2.10  | Leave             | Leave           |
               +---------+-------------------+-----------------+
               | 7.2.12  | Reform            | Takeon          |
               |         |                   | Substitute      |
               |         |                   | Search          |
               |         |                   | Replace         |
               |         |                   | Direct          |
               |         |                   | Update          |
               +---------+-------------------+-----------------+
               | 7.2.14  | Heartbeat         |                 |
               +---------+-------------------+-----------------+
               | 7.2.16  | NodeQuery         |                 |
               +---------+-------------------+-----------------+
               | 7.2.18  | Push              | Multicast       |
               +---------+-------------------+-----------------+

                   Figure 4: Mapping to P2PCast Messages

   The following sections describe the mapping of the P2PCast messages
   in more detail.

9.3.  Create

   This message will create a group with group_id.  This message MUST be
   delivered to the node whose node_id is closest to the group_id.  This
   node becomes the rendezvous point and root for the new multicast
   tree.  The rendezvous point will maintain f subtrees.





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9.4.  Join

   To join a multicast tree, a joining node N MUST send a Join request
   to a random node A already part of the tree.  Depending on the type
   of A, the joining algorithm continues as follows:

   o  Incomplete Node: Node A will arbitrarily select for which tree it
      wants to serve as an internal node and adopt N in that tree.  In
      the other tree, node N will adopt node A as a child (taking node
      A's place in the tree), thus becoming an internal node in the
      stripe that node A didn't choose.

   o  Only-Child Node: As this node has a parent that is an incomplete
      node, the joining node will be redirected to the parent node and
      will handle the request as detailed above.

   o  Complete Node: The contacted node A must be a leaf in the other
      tree.  If node A is a leaf node in Stripe 1, node N will become an
      internal node in Stripe 1, taking the place of node A and adopting
      it at the same time.  To find a place for itself in the other
      stripe, node N starts a random walk down the subtree rooted at the
      sibling of node A (if node A is the root and thus does not have
      siblings, node N is sent directly to a leaf in that tree), which
      ends as soon as node N finds an incomplete node or a leaf.  In
      this case, node N is adopted by the incomplete node.

   o  Special Node: as this node is a leaf in all subtrees, the joining
      node MAY adopt the node in one tree and become a child in the
      other.

   P2PCast uses defined messages for communication between nodes during
   reorganization.  To use P2PCast in this context, these messages are
   encapsulated by the message type Reform.  In doing so, the P2PCast
   message is to be included in the options parameter of Reform.  The
   following reorganization messages are defined by P2PCast:

      Takeon: To take another peer as a child

      Substitute: To take the place of a child of some peer

      Search: To obtain the child of a node in a particular stripe

      Replace: Different from Substitute in that the calling node that
      makes a node its child sheds off a random child

      Direct: To direct a node to its would-be parent

      Update: A node sends its updated state to its children



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   To adapt the P2PCast algorithm to the ALM Usage proposed here, after
   a Join request is accepted, a JoinAccept message MUST be returned to
   the joining node (one for every subtree).

9.5.  Leave

   When leaving a multicast group, a node will change its local state to
   indicate that it left the group.  Disregarding the case where the
   leaving node is the root of the tree, the leaving node must be
   complete or incomplete in its proper tree.  In the other trees, the
   node is a leaf and can just disappear by notifying its parent.  For
   the proper tree, if the node is incomplete, it is replaced by its
   child.  However, if the node is complete, a gap is created that is
   filled by a random child.  If this child is incomplete, it can simply
   fill the gap.  However, if it is complete, it needs to shed a random
   child.  This child is directed to its sibling, which sheds a random
   child.  This process ripples down the tree until the next-to-last
   level is reached.  The shed node is then taken as a child by the
   parent of the deleted node in the other stripe.

   Again, for the reorganization of the tree, the Reform message type is
   used as defined in the previous section.

9.6.  JoinConfirm

   This message is not part of the P2PCast protocol but is required by
   the basic protocol defined in this document.  Thus, the Usage MUST
   send this message to confirm a joining node accepting its parent
   node.  As with Join and JoinAccept, this MUST be carried out for
   every subtree.

9.7.  Multicast

   A message to be multicast to a group MUST be sent to the rendezvous
   node from where it is forwarded down the tree by being split into k
   stripes.  Each stripe is then sent via a subtree.  If a receiving
   node is a member of the tree rather than just a forwarder, it MAY
   pass the multicast data up to the application.

10.  Message Format

   All messages are mapped to the RELOAD experimental message type.  The
   mapping is shown in Figure 5.  The message codes are listed in
   Section 14.2.  The format of the body of a message is provided in
   [RELOAD].






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                +-------------------------+------------------+
                | Message                 |RELOAD Code Point |
                +-------------------------+------------------+
                | CreateALMTree           | exp_a_req        |
                +-------------------------+------------------+
                | CreateALMTreeResponse   | exp_a_ans        |
                +-------------------------+------------------+
                | Join                    | exp_a_req        |
                +-------------------------+------------------+
                | JoinAccept              | exp_a_ans        |
                +-------------------------+------------------+
                | JoinReject              | exp_a_ans        |
                +-------------------------+------------------+
                | JoinConfirm             | exp_a_req        |
                +-------------------------+------------------+
                | JoinConfirmResponse     | exp_a_ans        |
                +-------------------------+------------------+
                | JoinDecline             | exp_a_req        |
                +-------------------------+------------------+
                | JoinDeclineResponse     | exp_a_ans        |
                +-------------------------+------------------+
                | Leave                   | exp_a_req        |
                +-------------------------+------------------+
                | LeaveResponse           | exp_a_ans        |
                +-------------------------+------------------+
                | Reform                  | exp_a_req        |
                +-------------------------+------------------+
                | ReformResponse          | exp_a_ans        |
                +-------------------------+------------------+
                | Heartbeat               | exp_a_req        |
                +-------------------------+------------------+
                | HeartbeatResponse       | exp_a_ans        |
                +-------------------------+------------------+
                | NodeQuery               | exp_a_req        |
                +-------------------------+------------------+
                | NodeQueryResponse       | exp_a_ans        |
                +-------------------------+------------------+
                | Push                    | exp_a_req        |
                +-------------------------+------------------+
                | PushResponse            | exp_a_ans        |
                +-------------------------+------------------+

                   Figure 5: RELOAD Message Code Mapping








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   For Data Kind-IDs, the RELOAD specification [RELOAD] states: "Code
   points in the range 0xF0000001 to 0xFFFFFFFE are reserved for private
   use".  ALM Usage Kind-IDs are defined in the private use range.

   All ALM Usage messages map to the RELOAD Message Extension mechanism.

   Code points for the Kinds defined in this document MUST NOT conflict
   with any defined code points for RELOAD.  RELOAD defines exp_a_req
   and exp_a_ans for experimental purposes.  This specification uses
   only these message types for all ALM messages.  RELOAD defines the
   MessageContents data structure.  The ALM mapping uses the fields as
   follows:

   o  message_code: exp_a_req for requests and exp_a_ans for responses

   o  message_body: contains one instance of ALMHeader followed by one
      instance of ALMMessageContents

   o  extensions: unused

10.1.  ALMHeader Definition

   struct {
      uint32           sam_token;
      uint16           alm_algorithm_id;
      uint8            version;
   } ALMHeader;

   The fields in ALMHeader are used as follows:

      sam_token: The first four bytes identify this message as an ALM
      message.  This field MUST contain the value 0xD3414D42 (the string
      "SAMB" with the high bit of the first byte set).

      alm_algorithm_id: The ALM Algorithm ID of the ALM algorithm being
      used.  Each multicast tree uses only one algorithm.  Trees with
      different ALM algorithms can coexist and can share the same nodes.
      ALM Algorithm ID codes are defined in Section 14.1.

      version: The version of the ALM protocol being used.  This is a
      fixed-point integer between 0.1 and 25.4.  This document describes
      version 1.0 with a value of 0xA.









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10.2.  ALMMessageContents Definition

   struct {
      uint16       alm_message_code;
      opaque       alm_message_body;
   } ALMMessageContents;

   The fields in ALMMessageContents are used as follows:

      alm_message_code: This indicates the message being sent.  The
      message codes are listed in Section 14.2.

      alm_message_body: The message body itself, represented as a
      variable-length string of bytes.  The bytes themselves are
      dependent on the code value.  See Sections 8 and 9, which describe
      the various ALM methods for the definitions of the payload
      contents.

10.3.  Response Codes

   Response codes are defined in Section 6.3.3.1 of [RELOAD].  This
   specification maps to RELOAD ErrorResponse as follows:

   ErrorResponse.error_code = Error_Exp_A;

   Error_info contains an ALMErrorResponse instance.

   public struct {
      uint16   alm_error_code;
      opaque   alm_error_info<0..2^16-1>;
   } ALMErrorResponse;

   alm_error_code: The following error code values are defined.  Numeric
   values for these are defined in Section 14.3.

      Error_Unknown_Algorithm: The multicast algorithm is not known or
      not supported.

      Error_Child_Limit_Reached: The maximum number of child nodes has
      been reached for this node.

      Error_Node_Bandwidth_Reached: The overall data bandwidth limit
      through this node has been reached.

      Error_Node_Conn_Limit_Reached: The total number of connections to
      this node has been reached.





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      Error_Link_Cap_Limit_Reached: The capacity of a link has been
      reached.

      Error_Node_Mem_Limit_Reached: An internal memory capacity of the
      node has been reached.

      Error_Node_CPU_Cap_Limit_Reached: An internal processing capacity
      of the node has been reached.

      Error_Path_Limit_Reached: The maximum path length in hop count
      over the multicast tree has been reached.

      Error_Path_Delay_Limit_Reached: The maximum path length in message
      delay over the multicast tree has been reached.

      Error_Tree_Fanout_Limit_Reached: The maximum fanout of a multicast
      tree has been reached.

      Error_Tree_Depth_Limit_Reached: The maximum height of a multicast
      tree has been reached.

      Error_Other: A human-readable description is placed in the
      alm_error_info field.

11.  Examples

   All peers in the examples are assumed to have completed
   bootstrapping.  "Pn" refers to peer N.  "group_id" refers to a peer
   responsible for storing the ALMTree instance with group_id.






















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11.1.  Create Tree

   A node with "NODE-MATCH" rights sends a CreateALMTree request to the
   group_id node, which also has NODE-MATCH rights for its own address.
   The group_id node determines whether to create the new tree and, if
   so, performs a local StoreReq.  If the CreateALMTree succeeds, the
   ALMTree instance can be retrieved using Fetch.  An example message
   flow for creating a tree is depicted in Figure 6.

                P1      P2      P3       P4      group_id
                |       |       |        |       |
                |       |       |        |       |
                |       |       |        |       |
                | CreateALMTree |        |       |
                |------------------------------->|
                |       |       |        |       |
                |       |       |        |       | StoreReq
                |       |       |        |       |--+
                |       |       |        |       |  |
                |       |       |        |       |  |
                |       |       |        |       |<-+
                |       |       |        |       | StoreResponse
                |       |       |        |       |--+
                |       |       |        |       |  |
                |       |       |        |       |  |
                |       |       |        |       |<-+
                |       |       |        |       |
                |       |       |        |       |
                |       | CreateALMTreeResponse  |
                |<-------------------------------|
                |       |       |        |       |
                |       |       |        |       |
                | Fetch         |        |       |
                |------------------------------->|
                |       |       |        |       |
                |       |       |        |       |
                |       |         FetchResponse  |
                |<-------------------------------|
                |       |       |        |       |

             Figure 6: Message Flow Example for CreateALMTree

11.2.  Join Tree

   P1 joins node group_id as child node.  P2 joins the tree as a child
   of P1.  P4 joins the tree as a child of P1.  The corresponding
   message flow is shown in Figure 7.




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                   P1      P2      P3       P4      group_id
                   |       |       |        |       |
                   |       |       |        |       |
                   | Join                           |
                   |------------------------------->|
                   |       |       |        |       |
                   | JoinAccept                     |
                   |<-------------------------------|
                   |       |       |        |       |
                   |       |       |        |       |
                   |       |Join                    |
                   |       |----------------------->|
                   |       |       |        |       |
                   |                            Join|
                   |<-------------------------------|
                   |       |       |        |       |
                   |JoinAccept     |        |       |
                   |------>|       |        |       |
                   |       |       |        |       |
                   |JoinConfirm    |        |       |
                   |<------|       |        |       |
                   |       |       |        |       |
                   |       |       |        |Join   |
                   |       |       |        |------>|
                   |       |       |        |  Join |
                   |<-------------------------------|
                   |       |       |        |       |
                   | Join  |       |        |       |
                   |------>|       |        |       |
                   |       |       |        |       |
                   | JoinAccept    |        |       |
                   |----------------------->|       |
                   |       |       |        |       |
                   |       | JoinAccept     |       |
                   |       |--------------->|       |
                   |       |       |        |       |
                   |       |       |        |       |
                   |       |   JoinConfirm  |       |
                   |<-----------------------|       |
                   |       |       |        |       |
                   |       |   JoinDecline  |       |
                   |       |<---------------|       |
                   |       |       |        |       |
                   |       |       |        |       |

               Figure 7: Message Flow Example for Tree Join





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11.3.  Leave Tree

                   P1      P2      P3       P4      group_id
                   |       |       |        |       |
                   |       |       |        |       |
                   |       |       |  Leave |       |
                   |<-----------------------|       |
                   |       |       |        |       |
                   | LeaveResponse |        |       |
                   |----------------------->|       |
                   |       |       |        |       |
                   |       |       |        |       |

               Figure 8: Message Flow Example for Leave Tree





































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11.4.  Push Data

   The multicast data is pushed recursively P1 => group_id => P1 => P2,
   P4 following the tree topology created in the Join example above.  An
   example message flow is shown in Figure 9.

                   P1      P2      P3       P4      group_id
                   |       |       |        |       |
                   | Push  |       |        |       |
                   |------------------------------->|
                   |       |       |        |       |
                   |       |       |    PushResponse|
                   |<-------------------------------|
                   |       |       |        |       |
                   |       |       |        |   Push|
                   |<-------------------------------|
                   |       |       |        |       |
                   | PushResponse  |        |       |
                   |------------------------------->|
                   |       |       |        |       |
                   |Push   |       |        |       |
                   |------>|       |        |       |
                   |       |       |        |       |
                   |PushResponse   |        |       |
                   |<------|       |        |       |
                   |       |       |        |       |
                   | Push  |       |        |       |
                   |----------------------->|       |
                   |       |       |        |       |
                   |       |   PushResponse |       |
                   |<-----------------------|       |
                   |       |       |        |       |
                   |       |       |        |       |
                   |       |       |        |       |

              Figure 9: Message Flow Example for Pushing Data

12.  Kind Definitions

12.1.  ALMTree Kind Definition

   This section defines the ALMTree Kind per Section 7.4.5 of [RELOAD].
   An instance of the ALMTree Kind is stored in the overlay for each ALM
   tree instance.  It is stored at the address group_id.

   Kind-ID: 0xF0000001.  (This is a private-use code point per
   Section 14.6 of [RELOAD].)  The Resource Name for the ALMTree Kind-ID
   is the session_key used to identify the ALM tree.



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   Data Model: The data model is the ALMTree structure.

   Access Control: NODE-MATCH.  The node performing the store operation
   is required to have NODE-MATCH access.

   Meaning: The meaning of the fields is given in Section 7.2.1.

      struct {
        node_id peer_id;
        opaque session_key<0..2^32-1>;
        node_id group_id;
        Dictionary options;
      } ALMTree;

13.  RELOAD Configuration File Extensions

   There are no ALM parameters defined for the RELOAD configuration
   file.

14.  IANA Considerations

   This section contains the new code points registered by this
   document.

14.1.  ALM Algorithm Types

   IANA has created the "SAM ALM Algorithm IDs" registry.  Entries in
   this registry are 16-bit integers denoting Application-Layer
   Multicast algorithms as described in Section 10.1 of this document.
   Code points in the range 0x0003 to 0x7FFF SHALL be registered via
   RFC 5226 [RFC5226] Expert Review.  Code points in the range 0x8000 to
   0xFFFF are reserved for private use.  The initial contents of this
   registry are:

              +----------------+-------------------+-----------+
              | Algorithm Name | ALM Algorithm ID  | RFC       |
              +----------------+-------------------+-----------+
              | INVALID-ALG    |            0x0000 | RFC 7019  |
              | SCRIBE-SAM     |            0x0001 | RFC 7019  |
              | P2PCAST-SAM    |            0x0002 | RFC 7019  |
              | Reserved       |     0x8000-0xFFFF | RFC 7019  |
              +----------------+-------------------+-----------+

          Figure 10: "SAM ALM Algorithm IDs" Registry Allocations

   These values have been made available for the purposes of
   experimentation.  These values are not meant for vendor-specific use
   of any sort and MUST NOT be used for operational deployments.



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14.2.  Message Code Registration

   IANA has created the "SAM ALM Message Codes" registry.  Entries in
   this registry are 16-bit integers denoting message codes as described
   in Section 10.2 of this document.  Code points in the range 0x0014 to
   0x7FFF SHALL be registered via RFC 5226 [RFC5226] Expert Review.
   Code points in the range 0x8000 to 0xFFFF are reserved for private
   use.  The initial contents of this registry are:

        +-------------------------+----------------------+-----------+
        | Message Code Name       | Message Code Value   | RFC       |
        +-------------------------+----------------------+-----------+
        | InvalidMessageCode      |               0x0000 | RFC 7019  |
        | CreateALMTree           |               0x0001 | RFC 7019  |
        | CreateALMTreeResponse   |               0x0002 | RFC 7019  |
        | Join                    |               0x0003 | RFC 7019  |
        | JoinAccept              |               0x0004 | RFC 7019  |
        | JoinReject              |               0x0005 | RFC 7019  |
        | JoinConfirm             |               0x0006 | RFC 7019  |
        | JoinConfirmResponse     |               0x0007 | RFC 7019  |
        | JoinDecline             |               0x0008 | RFC 7019  |
        | JoinDeclineResponse     |               0x0009 | RFC 7019  |
        | Leave                   |               0x000A | RFC 7019  |
        | LeaveResponse           |               0x000B | RFC 7019  |
        | Reform                  |               0x000C | RFC 7019  |
        | ReformResponse          |               0x000D | RFC 7019  |
        | Heartbeat               |               0x000E | RFC 7019  |
        | HeartbeatResponse       |               0x000F | RFC 7019  |
        | NodeQuery               |               0x0010 | RFC 7019  |
        | NodeQueryResponse       |               0x0011 | RFC 7019  |
        | Push                    |               0x0012 | RFC 7019  |
        | PushResponse            |               0x0013 | RFC 7019  |
        | Reserved                |        0x8000-0xFFFF | RFC 7019  |
        +-------------------------+----------------------+-----------+

          Figure 11: "SAM ALM Message Codes" Registry Allocations

   These values have been made available for the purposes of
   experimentation.  These values are not meant for vendor-specific use
   of any sort and MUST NOT be used for operational deployments.

14.3.  Error Code Registration

   IANA has created the "SAM ALM Error Codes" registry.  Entries in this
   registry are 16-bit integers denoting error codes as described in
   Section 10.3 of this document.  Code points in the range 0x000D to





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   0x7FFF SHALL be registered via RFC 5226 [RFC5226] Expert Review.
   Code points in the range 0x8000 to 0xFFFF are reserved for private
   use.  The initial contents of this registry are:

      +----------------------------------+---------------+-----------+
      | Error Code Name                  | Code Value    | RFC       |
      +----------------------------------+---------------+-----------+
      | InvalidErrorCode                 |       0x0000  | RFC 7019  |
      | Error_Unknown_Algorithm          |       0x0001  | RFC 7019  |
      | Error_Child_Limit_Reached        |       0x0002  | RFC 7019  |
      | Error_Node_Bandwidth_Reached     |       0x0003  | RFC 7019  |
      | Error_Node_Conn_Limit_Reached    |       0x0004  | RFC 7019  |
      | Error_Link_Cap_Limit_Reached     |       0x0005  | RFC 7019  |
      | Error_Node_Mem_Limit_Reached     |       0x0006  | RFC 7019  |
      | Error_Node_CPU_Cap_Limit_Reached |       0x0007  | RFC 7019  |
      | Error_Path_Limit_Reached         |       0x0008  | RFC 7019  |
      | Error_Path_Delay_Limit_Reached   |       0x0009  | RFC 7019  |
      | Error_Tree_Fanout_Limit_Reached  |       0x000A  | RFC 7019  |
      | Error_Tree_Depth_Limit_Reached   |       0x000B  | RFC 7019  |
      | Error_Other                      |       0x000C  | RFC 7019  |
      | Reserved                         | 0x8000-0xFFFF | RFC 7019  |
      +----------------------------------+---------------+-----------+

           Figure 12: "SAM ALM Error Codes" Registry Allocations

   These values have been made available for the purposes of
   experimentation.  These values are not meant for vendor-specific use
   of any sort and MUST NOT be used for operational deployments.

15.  Security Considerations

   Overlays are vulnerable to DoS and collusion attacks.  We are not
   solving overlay security issues.  We assume that the node
   authentication model as defined in [RELOAD] will be used.

   Security issues specific to ALM Usage include the following:

   o  The right to create group_id at some node_id

   o  The right to store Tree info at some location in the DHT

   o  A limit on number of messages per second and bandwidth use

   o  The right to join an ALM tree







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16.  Acknowledgements

   Marc Petit-Huguenin, Michael Welzl, Joerg Ott, and Lars Eggert
   provided important comments on earlier versions of this document.

17.  References

17.1.  Normative Reference

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

17.2.  Informative References

   [BUFORD2008]  Buford, J. and H. Yu, "P2P: Overlay Multicast",
                 Encyclopedia of Wireless and Mobile Communications,
                 2008, <http://www.tandfonline.com/doi/abs/10.1081/
                 E-EWMC-120043583>.

   [BUFORD2009]  Buford, J., Yu, H., and E. Lua, "P2P Networking and
                 Applications (Chapter 9)", Morgan Kaufman, 2009,
                 <http://www.sciencedirect.com/science/book/
                 9780123742148>.

   [CASTRO2002]  Castro, M., Druschel, P., Kermarrec, A., and A.
                 Rowstron, "SCRIBE: A large-scale and decentralized
                 application-level multicast infrastructure", IEEE
                 Journal on Selected Areas in Communications, Vol. 20,
                 No. 8, October 2002, <http://ieeexplore.ieee.org/xpl/
                 login.jsp?tp=&arnumber=1038579>.

   [CASTRO2003]  Castro, M., Jones, M., Kermarrec, A., Rowstron, A.,
                 Theimer, M., Wang, H., and A. Wolman, "An Evaluation of
                 Scalable Application-level Multicast Built Using Peer-
                 to-peer Overlays", Proceedings of IEEE INFOCOM 2003,
                 April 2003, <http://ieeexplore.ieee.org/xpl/
                 login.jsp?tp=&arnumber=1208986>.

   [COMMON-API]  Waehlisch, M., Schmidt, T., and S. Venaas, "A Common
                 API for Transparent Hybrid Multicast", Work in
                 Progress, April 2013.

   [KOLBERG2010] Kolberg, M., "Employing Multicast in P2P Overlay
                 Networks", Handbook of Peer-to-Peer Networking, 2010,
                 <http://link.springer.com/content/pdf/
                 10.1007%2F978-0-387-09751-0_30.pdf>.





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   [P2PCAST]     Nicolosi, A. and S. Annapureddy, "P2PCast: A Peer-to-
                 Peer Multicast Scheme for Streaming Data", Stanford
                 Secure Computer Systems Group Report, May 2003,
                 <http://www.scs.stanford.edu/~reddy/research/p2pcast/
                 report.pdf>.

   [RELOAD]      Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset,
                 S., and H. Schulzrinne, "REsource LOcation And
                 Discovery (RELOAD) Base Protocol", Work in Progress,
                 February 2013.

   [RFC5226]     Narten, T. and H. Alvestrand, "Guidelines for Writing
                 an IANA Considerations Section in RFCs", BCP 26, RFC
                 5226, May 2008.

   [SAM-GENERIC] Muramoto, E., Imai, Y., and N. Kawaguchi, "Requirements
                 for Scalable Adaptive Multicast Framework in Non-GIG
                 Networks", Work in Progress, November 2006.

   [SPLITSTREAM] Castro, M., Druschel, P., Nandi, A., Kermarrec, A.,
                 Rowstron, A., and A. Singh, "SplitStream: High-
                 Bandwidth Multicast in a Cooperative Environment", SOSP
                 '03, Lake Bolton, New York, October 2003,
                 <http://dl.acm.org/citation.cfm?id=945474>.

Authors' Addresses

   John Buford
   Avaya Labs Research
   211 Mt. Airy Rd.
   Basking Ridge, New Jersey  07920
   USA

   Phone: +1 908 848 5675
   EMail: buford@avaya.com


   Mario Kolberg (editor)
   University of Stirling
   Dept. of Computing Science and Mathematics
   Stirling  FK9 4LA
   UK

   Phone: +44 1786 46 7440
   EMail: mkolberg@ieee.org
   URI:   http://www.cs.stir.ac.uk/~mko





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