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Versions: 00 01 02 03 04 05 06 RFC 7019

SAM Research Group                                             J. Buford
Internet-Draft                                       Avaya Labs Research
Intended status: Experimental                            M. Kolberg, Ed.
Expires: January 24, 2014                         University of Stirling
                                                           July 23, 2013


            Application Layer Multicast Extensions to RELOAD
               draft-irtf-samrg-sam-baseline-protocol-06

Abstract

   We define a RELOAD Usage for Application Layer Multicast 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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 24, 2014.

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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Overlay Network . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Overlay Multicast . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Source Specific Multicast (SSM) . . . . . . . . . . . . .   5
     2.4.  Any Source Multicast (ASM)  . . . . . . . . . . . . . . .   5
     2.5.  Peer  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Assumptions . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Overlay . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Overlay Multicast . . . . . . . . . . . . . . . . . . . .   6
     3.3.  RELOAD  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  NAT . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Tree Topology . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Architecture Extensions to RELOAD . . . . . . . . . . . . . .   7
   5.  RELOAD ALM Usage  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  ALM Tree Control Signaling  . . . . . . . . . . . . . . . . .   9
   7.  ALM Messages Mapped to RELOAD . . . . . . . . . . . . . . . .  10
     7.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .  10
     7.2.  Tree Lifecycle Messages . . . . . . . . . . . . . . . . .  11
       7.2.1.  Create Tree . . . . . . . . . . . . . . . . . . . . .  11
       7.2.2.  CreateTreeResponse  . . . . . . . . . . . . . . . . .  12
       7.2.3.  Join  . . . . . . . . . . . . . . . . . . . . . . . .  12
       7.2.4.  Join Accept (Join Response) . . . . . . . . . . . . .  14
       7.2.5.  Join Reject (Join Response) . . . . . . . . . . . . .  14
       7.2.6.  Join Confirm  . . . . . . . . . . . . . . . . . . . .  14
       7.2.7.  Join Confirm Response . . . . . . . . . . . . . . . .  15
       7.2.8.  Join Decline  . . . . . . . . . . . . . . . . . . . .  15
       7.2.9.  Join Decline Response . . . . . . . . . . . . . . . .  16
       7.2.10. Leave . . . . . . . . . . . . . . . . . . . . . . . .  16
       7.2.11. Leave Response  . . . . . . . . . . . . . . . . . . .  17
       7.2.12. Re-Form or Optimize Tree  . . . . . . . . . . . . . .  17
       7.2.13. Reform Response . . . . . . . . . . . . . . . . . . .  17
       7.2.14. Heartbeat . . . . . . . . . . . . . . . . . . . . . .  17
       7.2.15. Heartbeat Response  . . . . . . . . . . . . . . . . .  18
       7.2.16. NodeQuery . . . . . . . . . . . . . . . . . . . . . .  18
       7.2.17. NodeQuery Response  . . . . . . . . . . . . . . . . .  18
       7.2.18. Push  . . . . . . . . . . . . . . . . . . . . . . . .  21
       7.2.19. PushResponse  . . . . . . . . . . . . . . . . . . . .  21
   8.  Scribe Algorithm  . . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  22
     8.2.  Create  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     8.3.  Join  . . . . . . . . . . . . . . . . . . . . . . . . . .  23
     8.4.  Leave . . . . . . . . . . . . . . . . . . . . . . . . . .  23
     8.5.  JoinConfirm . . . . . . . . . . . . . . . . . . . . . . .  23
     8.6.  JoinDecline . . . . . . . . . . . . . . . . . . . . . . .  23



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     8.7.  Multicast . . . . . . . . . . . . . . . . . . . . . . . .  24
   9.  P2PCast Algorithm . . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  24
     9.2.  Message Mapping . . . . . . . . . . . . . . . . . . . . .  24
     9.3.  Create  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.4.  Join  . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.5.  Leave . . . . . . . . . . . . . . . . . . . . . . . . . .  26
     9.6.  JoinConfirm . . . . . . . . . . . . . . . . . . . . . . .  27
     9.7.  Multicast . . . . . . . . . . . . . . . . . . . . . . . .  27
   10. Message Format  . . . . . . . . . . . . . . . . . . . . . . .  27
     10.1.  ALMHeader Definition . . . . . . . . . . . . . . . . . .  29
     10.2.  ALMMessageContents Definition  . . . . . . . . . . . . .  29
     10.3.  Response Codes . . . . . . . . . . . . . . . . . . . . .  30
   11. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  31
     11.1.  Create Tree  . . . . . . . . . . . . . . . . . . . . . .  31
     11.2.  Join Tree  . . . . . . . . . . . . . . . . . . . . . . .  32
     11.3.  Leave Tree . . . . . . . . . . . . . . . . . . . . . . .  33
     11.4.  Push Data  . . . . . . . . . . . . . . . . . . . . . . .  33
   12. Kind Definitions  . . . . . . . . . . . . . . . . . . . . . .  34
     12.1.  ALMTree Kind Definition  . . . . . . . . . . . . . . . .  34
   13. RELOAD Configuration File Extensions  . . . . . . . . . . . .  34
   14. Change History  . . . . . . . . . . . . . . . . . . . . . . .  35
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
     15.1.  ALM Algorithm Types  . . . . . . . . . . . . . . . . . .  35
     15.2.  Message Code Registration  . . . . . . . . . . . . . . .  36
     15.3.  Error Code Registration  . . . . . . . . . . . . . . . .  36
   16. Security Considerations . . . . . . . . . . . . . . . . . . .  37
   17. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  38
   18. Informative References  . . . . . . . . . . . . . . . . . . .  38
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

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



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   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 [I-D.ietf-p2psip-base] 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.

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 2 of
   [I-D.ietf-p2psip-base], specifically the distinction between Node,
   Peer, and Client.

2.1.  Overlay Network

   Overlay network - An application layer virtual or logical network in
   which end points are addressable and 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



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   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
   which use proxies connected in an overlay multicast backbone "proxied
   overlay multicast" or POM.

2.3.  Source Specific Multicast (SSM)

   SSM tree: The creator of the tree is the source.  It sends data
   messages to the tree root which 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 remaining tree edges it is connected to.

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





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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 out-performed using
   separate overlays for each multicast session.  We use a single
   overlay rather than separate overlays per multicast sessions.

   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 which is closer
   to some of the entries than the current peer which 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 re-join operations for dislocated children
   nodes.

3.2.  Overlay Multicast

   The overlay supports concurrent multiple multicast trees.  The limit
   on 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 [I-D.ietf-p2psip-base] as the Peer-to-Peer 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





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   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, 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 plug-in for ALM algorithms handles the ALM state and
   control.  The ALM Algorithm is under control of the application via
   the Group API [I-D.irtf-samrg-common-api].

                                                        +---------+
                                                        |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:




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   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 tree, delay from
      source to leaf nodes, bandwidth use, packet loss rate.  In
      addition, diagnostic information may include statistics specific
      to the tree root, or to any node in the tree.

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 which require ALM functionality in the overlay.  Figure
   2 shows the internal structure of the ALM Usage.  This contains the
   Group API ([I-D.irtf-samrg-common-api]) an ALM algorithm plugin (e.g.
   Scribe) and the ALM messages which are then sent out to the RELOAD
   network.

   A RELOAD Usage is required [I-D.ietf-p2psip-base] 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  Addresses restoration of values after recovery from a network
      partition

   o  the types of connections that can be initiated using AppConnect

   an ALM GroupID is a RELOAD Node-ID.  The owner of an ALM group
   creates a RELOAD Node-ID as specified in [I-D.ietf-p2psip-base].
   This means that a GroupID is used as a RELOAD Destination for overlay
   routing purposes.



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6.  ALM Tree Control Signaling

   Peers use the overlay to support ALM operations such as:

   o  Create tree

   o  Join

   o  Leave

   o  Re-Form or optimize tree

   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, and to
   support 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 groupID is expected to be advertised or
   distributed out of band, perhaps by publishing in the DHT.
   Similarly, joining peers will discover the groupID out of band,
   perhaps by a lookup in the tree.

   As stated earlier, multiple algorithms will co-exist in the overlay.

   1.  Peer which initiates multicast group:


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


   2.  Any joining peer:





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


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

   3.  Leave Tree:

       leaveTree(groupID) // removes this node from the tree

       Propagates a leave message 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 message to its parent.  A
       child node receiving a leave message from a parent sends a join
       message to the groupID.

   4.  Message forwarding:

       multicastMsg(groupID, msg);

       For the 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
   [I-D.ietf-p2psip-base] 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 SAM
   framework overlay agnostic.

   As discussed in the SAM requirements document
   [I-D.muramoto-irtf-sam-generic-require], 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 life-cycle (create, join, leave, re-form, heartbeat)



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   o  Peer region and multicast properties

   The message codes are defined in Section 15.2 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.

   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
   [I-D.ietf-p2psip-base].  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 (application layer multicast)
   operations defined in this section.

7.2.1.  Create Tree

   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 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;






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   peer_id: the 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: the 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, heartbeat interval.

   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 Create Tree 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 Create Tree.  If the StoreReq fails, the Create Tree
   fails too.

   After a successful Create Tree, 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.  CreateTreeResponse

   After receiving a CreateTree message from node S, the peer sends a
   CreateTreeReponse to node S.

        struct {
          Dictionary options;
        } CreateTreeResponse;


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

7.2.3.  Join

   Causes the distributed algorithm for peer join of a specific ALM
   group to be invoked.  The definition of the Join message 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.




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


   peer_id: overlay address of joining/leaving peer

   group_id: the overlay address of the root of the tree

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

   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 then 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 then 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 behaviour can be described as follows:



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


7.2.4.  Join Accept (Join Response)

   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 a JoinConfirm
   message.  A JoinAccept which receives neither a JoinConfirm or
   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 which accepts the joining
   peer

   child_peer_id: overlay address of joining peer

   group_id: the overlay address of the root of the tree

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

7.2.5.  Join Reject (Join Response)

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

7.2.6.  Join Confirm

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




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      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 which is a child of
   the parent peer

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

   group_id: the overlay address of the root of the tree

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

   The JoinConfirm message behaviour is decribed 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.  Join Confirm Response

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

7.2.8.  Join Decline

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

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






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   peer_id: overlay address of joining peer which declines the
   JoinAccept

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

   group_id: the overlay address of the root of the tree

   The behaviour 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.  Join Decline Response

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

7.2.10.  Leave

   A peer which is part of an ALM tree identified by group_id which
   intends to detach from either a child or parent peer SHOULD send a
   Leave message to the peer it wishes to detach from.  A peer receiving
   a Leave message from a peer which is neither in its parent or 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: the overlay address of the root of the tree

   options: name-value list of options

   The behaviour of the Leave message 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)






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7.2.11.  Leave Response

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

7.2.12.  Re-Form or Optimize Tree

   This triggers a reorganization of either the entire tree or only a
   sub-tree.  It MAY include hints to specific peers of recommended
   parent or child peers to reconnect to.  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: the overlay address of the root of the tree

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

   options: name-value list of options

7.2.13.  Reform Response

   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 message from the unresponsive peer.  N is configurable.  RELOAD
   implementations are able to read a local configuration file for



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   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

7.2.15.  Heartbeat Response

   A parent node responds with a Heartbeat Response 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.  NodeQuery Response

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





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

      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.

      active_number_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 the number_active_trees.

      impl_info: information about the implementation of this usage

   public struct {
     uint32       tree_id;
     uint8        algorithm;
     NodeId       tree_root;
     uint8        number_parents;
     NodeId       parent<0..2^8-1>;
     Uint16       number_children_nodes;
     NodeId       children<0..2^16-1>;
     Uint32       path_length_to_root;
     Uint32       path_delay_to_root;



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     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 NodeId of each parent node

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

      children: the RELOAD NodeId of each child node

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

      path_delay_to_root: RTT in millisec. to root node

      path_delay_to_child: last measured RTT in msec to child node with
      largest RTT.

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


      join_confirm_timeout: The default time for join confirm/decline,
      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.






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      heartbeat timeout interval: 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

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 behaviour 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 PushReponse to node S.

      struct {
        Dictionary options;



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      } 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 which were forwarded the push message, and
   the number of adjacent nodes from which a PushResponse was received.

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          |
              +---------+-------------------+-----------------+
              | 7.2.2   | Join              | Join            |
              +---------+-------------------+-----------------+
              | 7.2.3   | JoinAccept        |                 |
              +---------+-------------------+-----------------+
              | 7.2.4   | JoinConfirm       |                 |
              +---------+-------------------+-----------------+
              | 7.2.5   | JoinDecline       |                 |
              +---------+-------------------+-----------------+
              | 7.2.6   | Leave             | Leave           |
              +---------+-------------------+-----------------+
              | 7.2.7   | Reform            |                 |
              +---------+-------------------+-----------------+
              | 7.2.8   | Heartbeat         |                 |
              +---------+-------------------+-----------------+
              | 7.2.9   | NodeQuery         |                 |
              +---------+-------------------+-----------------+
              | 7.2.10  | Push              | Multicast       |
              +---------+-------------------+-----------------+
              |         | Note 1            | deliver         |
              +---------+-------------------+-----------------+
              |         | Note 1            | forward         |
              +---------+-------------------+-----------------+
              |         | Note 1            | route           |
              +---------+-------------------+-----------------+
              |         | Note 1            | send            |
              +---------+-------------------+-----------------+



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                   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.

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
   rendevous point terminating the JOIN message from the child.

   To adapt the Scribe algorithm into 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 which has
   still children remaining after removing the leaving node.

8.5.  JoinConfirm

   This message is not part of the Scribe protocol, but 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.





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8.7.  Multicast

   A message to be multicast to a group MUST be sent to the rendevous
   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.

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).  The remainder of this section will assume f=2 for the
   discussion.  This is to keep the complexity for the description down.
   However, the algorithm scales for any number f.

   P2PCast distinguishes the following types of nodes:

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

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

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

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

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 |



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               +---------+-------------------+-----------------+
               | 7.2.1   | CreateALMTree     | Create          |
               +---------+-------------------+-----------------+
               | 7.2.2   | Join              | Join            |
               +---------+-------------------+-----------------+
               | 7.2.3   | JoinAccept        |                 |
               +---------+-------------------+-----------------+
               | 7.2.4   | JoinConfirm       |                 |
               +---------+-------------------+-----------------+
               | 7.2.5   | JoinDecline       |                 |
               +---------+-------------------+-----------------+
               | 7.2.6   | Leave             | Leave           |
               +---------+-------------------+-----------------+
               | 7.2.7   | Reform            | Takeon          |
               |         |                   | Substitute      |
               |         |                   | Search          |
               |         |                   | Replace         |
               |         |                   | Direct          |
               |         |                   | Update          |
               +---------+-------------------+-----------------+
               | 7.2.8   | Heartbeat         |                 |
               +---------+-------------------+-----------------+
               | 7.2.9   | NodeQuery         |                 |
               +---------+-------------------+-----------------+
               | 7.2.10  | 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.

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 of the type of A
   the joining algorithm continues as follows:

   o  Incomplete Nodes: 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



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      A's place in the tree) thus becoming an internal node in the
      stripe that node A didn't choose.

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

   o  Complete Nodes: 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, 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
   reorganisation.  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 reorganisation 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 node which makes us
      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

   To adapt the P2PCast algorithm into 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



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   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 which 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 reorganisation 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 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 given in the following table.  The message codes are given
   in Section 15.2.  The format of the body of a message is given in
   Figure 5.

                +-------------------------+------------------+
                | Message                 |RELOAD Code Point |
                +-------------------------+------------------+
                | CreateALMTree           | exp_a_req        |
                +-------------------------+------------------+
                | CreateALMTreeResponse   | exp_a_ans        |
                +-------------------------+------------------+
                | Join                    | exp_a_req        |
                +-------------------------+------------------+
                | JoinAccept              | exp_a_ans        |
                +-------------------------+------------------+



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                | 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

   For Data Kind-IDs, the RELOAD specification 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,
   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




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   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 Algorith ID of the ALM algorithm being
      used.  Each multicast tree uses only one algorithm.  Trees with
      different ALM algorithms can co-exist, and can share the same
      nodes.  ALM Algorithm ID codes are defined in Section 15.1

      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.

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 15.2.

      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 Section 8 and Section 9
      describing the various ALM methods for the definitions of the
      payload contents.




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10.3.  Response Codes

   Response codes are defined in section 6.3.3.1 in 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 Section 15.3.

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

      Error_Child_Limit_Reached: The maximum number of children 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

      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 hopcount 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




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      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.  "GroupID" refers to a peer
   responsible for storing the ALMTree instance with GroupID.

11.1.  Create Tree

   A node with "NODE-MATCH" rights sends a request CreateTree 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 CreateTree succeeds, the
   ALMTree instance can be retrieved using Fetch.  An example message
   flow for ceating a tree is depicted in Figure 6.

                P1      P2      P3       P4      GroupID
                |       |       |        |       |
                |       |       |        |       |
                |       |       |        |       |
                | CreateTree    |        |       |
                |------------------------------->|
                |       |       |        |       |
                |       |       |        |       | StoreReq
                |       |       |        |       |--+
                |       |       |        |       |  |
                |       |       |        |       |  |
                |       |       |        |       |<-+
                |       |       |        |       | StoreResponse
                |       |       |        |       |--+
                |       |       |        |       |  |
                |       |       |        |       |  |
                |       |       |        |       |<-+
                |       |       |        |       |
                |       |       |        |       |
                |       |    CreateTreeResponse  |
                |<-------------------------------|
                |       |       |        |       |
                |       |       |        |       |
                | Fetch         |        |       |
                |------------------------------->|
                |       |       |        |       |
                |       |       |        |       |



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                |       |         FetchResponse  |
                |<-------------------------------|
                |       |       |        |       |

              Figure 6: Message flow example for CreateTree.

11.2.  Join Tree

   P1 joins node GroupID 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.

                    P1      P2      P3       P4      GroupID
                    |       |       |        |       |
                    |       |       |        |       |
                    | Join                           |
                    |------------------------------->|
                    |       |       |        |       |
                    | JoinAccept                     |
                    |<-------------------------------|
                    |       |       |        |       |
                    |       |       |        |       |
                    |       |Join                    |
                    |       |----------------------->|
                    |       |       |        |       |
                    |                            Join|
                    |<-------------------------------|
                    |       |       |        |       |
                    |JoinAccept     |        |       |
                    |------>|       |        |       |
                    |       |       |        |       |
                    |JoinConfirm    |        |       |
                    |<------|       |        |       |
                    |       |       |        |       |
                    |       |       |        |Join   |
                    |       |       |        |------>|
                    |       |       |        |  Join |
                    |<-------------------------------|
                    |       |       |        |       |
                    | Join  |       |        |       |
                    |------>|       |        |       |
                    |       |       |        |       |
                    | JoinAccept    |        |       |
                    |----------------------->|       |
                    |       |       |        |       |
                    |       | JoinAccept     |       |
                    |       |--------------->|       |
                    |       |       |        |       |



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                    |       |       |        |       |
                    |       |   Join Confirm |       |
                    |<-----------------------|       |
                    |       |       |        |       |
                    |       |   Join Decline |       |
                    |       |<---------------|       |
                    |       |       |        |       |
                    |       |       |        |       |

               Figure 7: Message flow example for tree Join.

11.3.  Leave Tree

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

              Figure 8: Message flow example for Leave tree.

11.4.  Push Data

   The multicast data is pushed recursively P1 => GroupID => 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      GroupID
                    |       |       |        |       |
                    | Push  |       |        |       |
                    |------------------------------->|
                    |       |       |        |       |
                    |       |       |    PushResponse|
                    |<-------------------------------|
                    |       |       |        |       |
                    |       |       |        |   Push|
                    |<-------------------------------|
                    |       |       |        |       |
                    | PushResponse  |        |       |
                    |------------------------------->|
                    |       |       |        |       |
                    |Push   |       |        |       |
                    |------>|       |        |       |



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                    |       |       |        |       |
                    |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 in 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.

   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.





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14.  Change History

   o  Version 02: Remove Hybrid ALM material.  Define ALMTree kind.
      Define new RELOAD messages.  Define RELOAD architecture
      extensions.  Add Scribe as base algorithm for ALM usage.  Define
      code points.  Define preliminary ALM-specific security issues.

   o  Version 03: Add P2Pcast Algorithm.

   o  Version 04: Add mapping to RELOAD experimental message.  Modified
      IANA considerations section.  Changed category of id from
      Informational to Experimental.  New algorithm identification
      coding.  New message coding.  Added push message.  Create Tree
      access policy changed to use NODE-MATCH.  Create Tree StoreReq
      clarified.  Updated the diagrams in the Examples section.  Added a
      Push data example.  Defined the ALMTree kind.

   Version 05: Updated references.  Fixed typos.

   Version 06: Fixed typos.

15.  IANA Considerations

   This section contains the new code points registered by this
   document.  [NOTE TO IANA/RFC-EDITOR: Please replace RFC-to-be with
   the RFC number for this specification in the following list. ]

15.1.  ALM Algorithm Types

   We request that IANA create a "SAM ALM Algorithm ID" Registry.
   Entries in this registry are 16-bit integers denoting Application
   Layer Multicast algorithms as described in section Section 10.1 of
   [RFC-to-be].  Code points in the range 0x3 to 0x7fff SHALL be
   registered via RFC 5226 [RFC5226] Expert Review.  Code points in the
   range 0x7fff to 0xfffe are reserved for private use.  The initial
   contents of this registry are:

              +----------------+-------------------+-----------+
              | Algorithm Name | ALM Algorith ID   | RFC       |
              +----------------+-------------------+-----------+
              | INVALID-ALG    |                 0 | RFC-to-be |
              | SCRIBE-SAM     |                 1 | RFC-to-be |
              | P2PCAST-SAM    |                 2 | RFC-to-be |
              | Reserved       |       0x3..0xffff | RFC-to-be |
              +----------------+-------------------+-----------+

                                 Figure 10




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   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.

15.2.  Message Code Registration

   We request that IANA create a "SAM ALM Message Code" Registry.
   Entries in this registry are 16-bit integers denoting message codes
   as described in section Section 10.2 of [RFC-to-be].  Code points in
   the range 0x14 to 0x7fff SHALL be registered via RFC 5226 [RFC5226]
   Expert Review.  Code points in the range 0x7fff to 0xfffe are
   reserved for private use.  The initial contents of this registry are:

        +-------------------------+----------------------+-----------+
        | Message Code Name       | Message Code Value   | RFC       |
        +-------------------------+----------------------+-----------+
        | InvalidMessageCode      |                    0 | RFC-to-be |
        | CreateALMTRee           |                    1 | RFC-to-be |
        | CreateALMTreeResponse   |                    2 | RFC-to-be |
        | Join                    |                    3 | RFC-to-be |
        | JoinAccept              |                    4 | RFC-to-be |
        | JoinReject              |                    5 | RFC-to-be |
        | JoinConfirm             |                    6 | RFC-to-be |
        | JoinConfirmResponse     |                    7 | RFC-to-be |
        | JoinDecline             |                    8 | RFC-to-be |
        | JoinDeclineResponse     |                    9 | RFC-to-be |
        | Leave                   |                   10 | RFC-to-be |
        | LeaveResponse           |                   11 | RFC-to-be |
        | Reform                  |                   12 | RFC-to-be |
        | ReformResponse          |                   13 | RFC-to-be |
        | Heartbeat               |                   14 | RFC-to-be |
        | HeartbeatResponse       |                   15 | RFC-to-be |
        | NodeQuery               |                   16 | RFC-to-be |
        | NodeQueryResponse       |                   17 | RFC-to-be |
        | Push                    |                   18 | RFC-to-be |
        | PushResponse            |                   19 | RFC-to-be |
        | Reserved                |         0x14..0xffff | RFC-to-be |
        +-------------------------+----------------------+-----------+

                                 Figure 11

   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.

15.3.  Error Code Registration





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   We request that IANA create a "SAM ALM Error Code" Registry.  Entries
   in this registry are 16-bit integers denoting error codes as
   described in section Section 10.3 of [RFC-to-be].  Code points in the
   range 0x14 to 0x7fff SHALL be registered via RFC 5226 [RFC5226]
   Expert Review.  Code points in the range 0x7fff to 0xfffe are
   reserved for private use.  The initial contents of this registry are:

       +----------------------------------+--------------+-----------+
       | Error Code Name                  | Code Value   | RFC       |
       +----------------------------------+--------------+-----------+
       | InvalidErrorCode                 |            0 | RFC-to-be |
       | Error_Unknown_Algorithm          |            1 | RFC-to-be |
       | Error_Child_Limit_Reached        |            2 | RFC-to-be |
       | Error_Node_Bandwidth_Reached     |            3 | RFC-to-be |
       | Error_Node_Conn_Limit_Reached    |            4 | RFC-to-be |
       | Error_Link_Cap_Limit_Reached     |            5 | RFC-to-be |
       | Error_Node_Mem_Limit_Reached     |            6 | RFC-to-be |
       | Error_Node_CPU_Cap_Limit_Reached |            7 | RFC-to-be |
       | Error_Path_Limit_Reached         |            8 | RFC-to-be |
       | Error_Path_Delay_Limit_Reached   |            9 | RFC-to-be |
       | Error_Tree_Fanout_Limit_Reached  |           10 | RFC-to-be |
       | Error_Tree_Depth_Limit_Reached   |           11 | RFC-to-be |
       | Error_Other                      |           12 | RFC-to-be |
       | Reserved                         | 0x0D..0xffff | RFC-to-be |
       +----------------------------------+--------------+-----------+

                                 Figure 12

   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.

16.  Security Considerations

   Overlays are vulnerable to DOS and collusion attacks.  We are not
   solving overlay security issues.  We assume the node authentication
   model as defined in [I-D.ietf-p2psip-base].

   ALM Usage specific security issues:

   o  Right to create GroupID at some node_id

   o  Right to store Tree info at some Location in the DHT

   o  Limit on # messages / sec and bandwidth use

   o  Right to join an ALM tree




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17.  Acknowledgement

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

18.  Informative References

   [BUFORD2008]
              Buford, J. and H. Yu, "Peer-to-Peer Overlay Multicast",
              Encyclopedia of Wireless and Mobile Communications 2008,
              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, 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://
              research.microsoft.com/en-us/um/people/antr/past/
              jsac.pdf>.

   [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://research.microsoft.com/en-us/um/people/
              mcastro/publications/infocom-compare.pdf>.

   [I-D.ietf-p2psip-base]
              Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
              H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
              Base Protocol", draft-ietf-p2psip-base-26 (work in
              progress), February 2013.

   [I-D.irtf-samrg-common-api]
              Waehlisch, M., Schmidt, T., and S. Venaas, "A Common API
              for Transparent Hybrid Multicast", draft-irtf-samrg-
              common-api-06 (work in progress), August 2012.

   [I-D.muramoto-irtf-sam-generic-require]
              Muramoto, E., "Requirements for Scalable Adaptive
              Multicast Framework in Non-GIG Networks", draft-muramoto-



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              irtf-sam-generic-require-01 (work in progress), November
              2006.

   [KOLBERG2010]
              Kolberg, M., "Employing Multicast in P2P Networks",
              Handbook of Peer-to-Peer Networking (Ed. X.Shen, H. Yu, J.
              Buford, M. Akon) 2010, 2010, <http://link.springer.com/
              content/pdf/10.1007%2F978-0-387-09751-0_30.pdf>.

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

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

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552, July
              2003.

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

   [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 2003, October 2003, <http://
              research.microsoft.com/en-us/um/people/antr/PAST/
              SplitStream-sosp.pdf>.

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








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   Mario Kolberg (editor)
   University of Stirling
   Dept. 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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