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Versions: 00 01

SAM Research Group                                             J. Buford
Internet-Draft                                       Avaya Labs Research
Intended status: Informational                           M. Kolberg, Ed.
Expires: February 4, 2013                         University of Stirling
                                                            T C. Schmidt
                                                             HAW Hamburg
                                                            M. Waehlisch
                                                    link-lab & FU Berlin
                                                         August 03, 2012


            Application Layer Multicast Extensions to RELOAD
                  draft-samrg-sam-baseline-protocol-01

Abstract

   We define a RELOAD Usage for Application Layer Multicast as well as
   extensions to RELOAD message layer to support ALM.  The ALM Usage is
   intended to support a variety of ALM control algorithms in an
   overlay-independent way.  Scribe is defined as an example algorithm.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 4, 2013.

Copyright Notice

   Copyright (c) 2012 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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Overlay Network  . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Overlay Multicast  . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Peer . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Overlay  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Overlay Multicast  . . . . . . . . . . . . . . . . . . . .  6
     3.3.  RELOAD . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     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 Added to RELOAD Protocol  . . . . . . . . . . . . 11
     7.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 11
     7.2.  Tree Lifecycle Messages  . . . . . . . . . . . . . . . . . 12
       7.2.1.  Create Tree  . . . . . . . . . . . . . . . . . . . . . 12
       7.2.2.  Join . . . . . . . . . . . . . . . . . . . . . . . . . 13
       7.2.3.  Join Accept  . . . . . . . . . . . . . . . . . . . . . 13
       7.2.4.  Join Confirm . . . . . . . . . . . . . . . . . . . . . 14
       7.2.5.  Join Decline . . . . . . . . . . . . . . . . . . . . . 14
       7.2.6.  Leave  . . . . . . . . . . . . . . . . . . . . . . . . 14
       7.2.7.  Re-Form or Optimize Tree . . . . . . . . . . . . . . . 15
       7.2.8.  Heartbeat  . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Scribe Algorithm . . . . . . . . . . . . . . . . . . . . . . . 16
     8.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 16
     8.2.  Create . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.3.  Join . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.4.  Leave  . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.5.  JoinConfirm  . . . . . . . . . . . . . . . . . . . . . . . 18
     8.6.  JoinDecline  . . . . . . . . . . . . . . . . . . . . . . . 19
     8.7.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 19
   9.  P2PCast Algorithm Plug-in  . . . . . . . . . . . . . . . . . . 19
     9.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.2.  Create . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     9.3.  Join . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     9.4.  Leave  . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     9.5.  JoinConfirm  . . . . . . . . . . . . . . . . . . . . . . . 21



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     9.6.  JoinDecline  . . . . . . . . . . . . . . . . . . . . . . . 21
     9.7.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 22
   10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     10.1. Create Tree  . . . . . . . . . . . . . . . . . . . . . . . 22
     10.2. Join Tree  . . . . . . . . . . . . . . . . . . . . . . . . 23
     10.3. Leave Tree . . . . . . . . . . . . . . . . . . . . . . . . 24
     10.4. Add Direct Application Edge  . . . . . . . . . . . . . . . 24
     10.5. Adjust Tree to Churn . . . . . . . . . . . . . . . . . . . 24
     10.6. Push Data  . . . . . . . . . . . . . . . . . . . . . . . . 24
   11. Kind Definitions . . . . . . . . . . . . . . . . . . . . . . . 24
     11.1. ALMTree Kind Definition  . . . . . . . . . . . . . . . . . 24
   12. Configuration File Extensions  . . . . . . . . . . . . . . . . 24
   13. Change History . . . . . . . . . . . . . . . . . . . . . . . . 25
   14. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 25
   15. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   16. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     17.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Additional Stuff  . . . . . . . . . . . . . . . . . . 29
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29






























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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 connect nodes over global internet

   Adaptability includes

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

   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



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   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

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

                                 Figure 1

   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 the above figure, "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.

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.  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.  Peer

   Peer: an autonomous end system that is connected to the physical
   network and participates in and contributes resources to overlay



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   construction, routing and maintenance.  Some peers may also perform
   additional roles such as connection relays, super nodes, NAT
   traversal, 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 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 distibuted hash table
   (DHT) for data storage and overlay by which the peers interconnect
   and route messages.  RELOAD is a generic P2P overlay, and application
   support is defined by profiles called Usages.






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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, 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, shown in the figure below.  New ALM messages
   are added to RELOAD Message Transport.  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].






























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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

   The ALM components interact with RELOAD as follows:

   o  ALM uses the RELOAD data storage functionality to store a 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 tree, including average number of tree, delay from
      source to leaf nodes, bandwidth use, lost packet 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 be can
   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.  The
   figure below 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  Register Kind-Id points

   o  Define data structures for each kind

   o  Defines access control rules for each kind

   o  Defines the Resource Name used to hash to the Resource ID where
      the kind is stored

   o  Addresses restoration of values after recovery from a network
      partition

   o  Defines the types of connections that can be initiated using
      AppConnect

   A ALM GroupID is a RELOAD Node-ID.  The owner of a 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.


6.  ALM Tree Control Signaling

   Peers use the overlay to support ALM operations such as:

   o  Create tree

   o  Join




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   o  Leave

   o  Re-Form or optimize tree

   There are a variety of algorithms for peers to form multicast trees
   in the overlay.  We permit multiple such algorithms to be supported
   in the overlay, since different algorithms may be more suitable for
   certain application requirements, and since we wish 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 algorithm for forming a multicast tree in the
   overlay.  Its main advantage is use of the overlay routing mechanism
   for routing both control and data messages.  The group creator
   doesn't have to be the root of the tree or even in the tree.  It
   doesn't consider per node load, admission control, or alternative
   paths.

   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
                        // out of band advertisement or
                        // distribution of groupID,
                        // perhaps by publishing in DHT

                                   Figure 3

   2.  Any joining peer:


   // out of band discovery of groupID, perhaps by lookup in DHT
   joinTree(groupID); // sends "join groupID" message

                                   Figure 4


       The overlay routes the join request using the overlay routing



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       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);

   5.  For the message forwarding there are two approaches:

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

       *  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.


7.  ALM Messages Added to RELOAD Protocol

7.1.  Introduction

   In this document we define messages for overlay multicast tree
   creation, using an existing proposal (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
   [I-D.irtf-sam-hybrid-overlay-framework] (hereafter SAM framework) can
   be used with P2P-SIP, and that the SAM framework is overlay agnostic.

   As discussed in the SAM requirements draft, 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.




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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 GroupId.  The usual interpretation of GroupId is that the peer
   with peer id closest to and less than the GroupId is the root of the
   tree.  The tree has no children at the time it is created.

   The GroupId 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 GroupId from the SessionKey MUST be done using the
   overlay's id generation mechanism.

   A successful Create Tree causes an ALMTree structure to be stored in
   the overlay at the node responsible for NodeID equal to the GroupId.

         struct {
           NodeID PeerId;
           opaque SessionKey<0..2^32-1>;
           NodeID GroupId;
           Dictionary Options;
         } ALMTree;

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

   SessionKey: a well-known string when hashed using the overlay's id
   generation algorithm produces the GroupId.

   GroupId: 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 an Store
   operation.  Before the Store of an ALMTree structure is permitted,
   the storing peer MUST check that:

   o  The certificate contains a SessionKey

   o  The certificate contains a Node-ID that is the same as GroupID
      that it is being stored at Node-ID (this is the NODE-MATCH access



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      policy)

7.2.2.  Join

   Causes the distributed algorithm for peer join of a specific ALM
   group to be invoked.  If successful, the PeerId 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 {
           NodeID PeerId;
           NodeID GroupId;
           Dictionary Options;
         } Join;

   PeerId: overlay address of joining/leaving peer

   GroupId: the overlay address of the root of the tree

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

7.2.3.  Join Accept

   Tells the requesting joining peer that the indicated peer is
   available to act as its parent in the ALM tree specified by GroupId,
   with the corresponding Options specified.  A peer MAY receive more
   than one JoinAccept from diffent candidate parent peers in the
   GroupId tree.  The peer accepts a peer as parent using a JoinConfirm
   message.  A JoinAccept which receives neither a JoinConfirm or
   JoinDecline response MUST expire.

         struct {
           NodeID ParentPeerId;
           NodeID ChildPeerId;
           NodeID GroupId;
           Dictionary Options;
         } JoinAccept;

   ParentPeerId: overlay address of a peer which accepts the joining
   peer

   ChildPeerId: overlay address of joining peer

   GroupId: the overlay address of the root of the tree

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





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7.2.4.  Join Confirm

   A peer receiving a JoinAccept message which it wishes to accept MUST
   explicitly accept it before the expiration of the JoinAccept 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.

         struct {
           NodeID ChildPeerId;
           NodeID ParentPeerId;
           NodeID GroupId;
           Dictionary Options;
         } JoinConfirm;

   ChildPeerId: overlay address of joining peer which is a child of the
   parent peer

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

   GroupId: the overlay address of the root of the tree

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

7.2.5.  Join Decline

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

         struct {
           NodeID PeerId;
           NodeID ParentPeerId;
           NodeID GroupId;
         } JoinDecline;

   PeerId: overlay address of joining peer which declines the JoinAccept

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

   GroupId: the overlay address of the root of the tree

7.2.6.  Leave

   A peer which is part of an ALM tree idenfied by GroupId 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



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   Leave message from a peer which is neither in its parent or child
   lists SHOULD ignore the message.

         struct {
           NodeID PeerId;
           NodeID GroupId;
           Dictionary Options;
         } Leave;

   PeerId: overlay address of leaving peer

   GroupId: the overlay address of the root of the tree

   Options: name-value list of options

7.2.7.  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 {
           NodeID GroupId;
           NodeID PeerId;
           Dictionary Options;
         } Reform;

   GroupId: the overlay address of the root of the tree

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

   Options: name-value list of options

7.2.8.  Heartbeat

   A node signals to its adjacent nodes in the tree that it is alive.
   If a peer 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.







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         struct {
           NodeID PeerId1;
           NodeID PeerId2;
           NodeID GroupId;
         } Heartbeat;

   PeerId1: source of heartbeat

   PeerId2: destination of heartbeat

   GroupId: overlay address of the root of the tree


8.  Scribe Algorithm

8.1.  Overview

   The following table shows a mapping between RELOAD ALM messages (as
   defined in Section 5 of this draft) and Scribe messages as defined in
   [CASTRO2002].































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            +------------------+-------------------+-----------------+
            | Section in Draft |RELOAD ALM Message | Scribe Message  |
            +------------------+-------------------+-----------------+
            | 5.2.1            | CreateALMTree     | Create          |
            +------------------+-------------------+-----------------+
            | 5.2.2            | Join              | Join            |
            +------------------+-------------------+-----------------+
            | 5.2.3            | JoinAccept        |                 |
            +------------------+-------------------+-----------------+
            | 5.2.4            | JoinConfirm       |                 |
            +------------------+-------------------+-----------------+
            | 5.2.5            | JoinDecline       |                 |
            +------------------+-------------------+-----------------+
            | 5.2.8            | Leave             | Leave           |
            +------------------+-------------------+-----------------+
            | 5.2.10           | Reform            |                 |
            +------------------+-------------------+-----------------+
            | 5.2.11           | Heartbeat         |                 |
            +------------------+-------------------+-----------------+
            | new              | Push/Deliver/Send | Multicast       |
            +------------------+-------------------+-----------------+
            |                  | Note 1            | deliver         |
            +------------------+-------------------+-----------------+
            |                  | Note 1            | forward         |
            +------------------+-------------------+-----------------+
            |                  | Note 1            | route           |
            +------------------+-------------------+-----------------+
            |                  | Note 1            | send            |
            +------------------+-------------------+-----------------+

                                 Figure 5

   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 GroupId.  This message will be
   delivered to the node whose NodeId is closest to the GroupId.  This
   node becomes the rendevous point and root for the new multicast tree.
   Groups may have multiple sources of multicast messages.

   CREATE : groups.add(msg.GroupId)

   GroupId: the overlay address of the root of the tree





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8.3.  Join

   To join a multicast tree a node sends a JOIN request with the GroupId
   as the key.  This message gets routed by the overlay to the rendevous
   point of the tree.  If an intermediate node is already a forwarder
   for this tree, it will add the joining node as a child.  Otherwise
   the node will create a child table for the group and adds the joining
   node.  It will 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 is returned to the
   joining node.

   JOIN : if(checkAccept(msg)) {
                       recvJoins.add(msg.source, msgGroupId)
                       SEND(JOINAccept(nodeID, msg.source, msg.GroupId))
                   }

8.4.  Leave

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

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

8.5.  JoinConfirm

   This message is not part of the Scribe protocol, but required by the
   basic protocol proposed in this draft.  Thus the usage will send this
   message to conirm a joining node accepting its parent node.

   JOINConfirm: if(recvJoins.contains(msg.source,msg.GroupId)){
                    if !(groups.contains(msg.GroupId)) {
                      groups.add(msg.GroupId)
                      SEND(msg,msg.GroupId)
                    }
                   groups[msg.GroupId].children.add(msg.source)
                            recvJoins.del(msg.source, msgGroupId)
                 }






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8.6.  JoinDecline

   JOINDecline: if(recvJoins.contains(msg.source,msg.GroupId))
                            recvJoins.del(msg.source, msgGroupId)

8.7.  Multicast

   A message to be multicast to a group is 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 will pass the multicast data
   up to the application.

   MULTICAST : foreach(groups[msg.GroupId].children as NodeId)
                      SEND(msg,NodeId)
               if memberOf(msg.GroupId)
                      invokeMessageHandler(msg.GroupId, msg)


9.  P2PCast Algorithm Plug-in

9.1.  Overview

   P2PCast [P2PCAST]creates a forest of related trees to increase load
   balancing.  P2PCast is independent on 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




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

9.2.  Create

   This message will create a group with group_id.  This message will 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.

9.3.  Join

   To join a multicast tree a joining node N sends 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: 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 N will adopt A as a child (taking A's place in the
      tree) thus becoming an internal node in the stripe that 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 A is a leaf node in Stripe 1, N will become an internal
      node in Stripe 1, taking the place of A, adopting it at the same
      time.  To find a place for itself in the other stripe, N starts a
      random walk down the subtree rooted at the sibling of A (if A is
      the root and thus does not have sublings, N is sent directly to a
      leaf in that tree), which ends as soon as N finds an incomplete
      node or a leaf.  In this case N is adopted by the incomplete node.

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

   P2PCast uses defined messages for communication between nodes during
   reorganisation.  Here these messages are encapsulated by the message
   type REFORM is used.  The P2PCast message is included in the Options
   parameter of REFORM.  The following messages are defined by P2PCast:

      TAKEON: To take another peer as a child

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




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      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 wouldbe 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 is returned to
   the joining node (one for every subtree).

9.4.  Leave

   When leaving a multicast group a node will change its local state to
   indicate that it left the group.  Distregarding 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 bubble 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.

9.5.  JoinConfirm

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

9.6.  JoinDecline

   JOINDecline: if(recvJoins.contains(msg.source,msg.group_id))
                            recvJoins.del(msg.source, msggroup_id)








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9.7.  Multicast

   A message to be multicast to a group is 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 will
   pass the multicast data up to the application.


10.  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.

10.1.  Create Tree

        P1      P2      P3       P4      GroupID
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |
        | CreateTree    |        |       |
        |------------------------------->|
        |       |       |        |       |
        |       |       |        |       |
        |       |    CreateTreeResponse  |
        |<-------------------------------|
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |
        |       |       |        |       |

                                 Figure 6















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10.2.  Join Tree

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

                                 Figure 7



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10.3.  Leave Tree

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

                                 Figure 8

10.4.  Add Direct Application Edge

10.5.  Adjust Tree to Churn

10.6.  Push Data


11.  Kind Definitions

11.1.  ALMTree Kind Definition

   This section defines the ALMTree kind.

   Kind IDs The Resource Name for the ALMTree Kind-ID is the SessionKey
   used to identify the ALM tree

   Data Model The data model is the ALMTree structure.

   Access Control NODE-MATCH


12.  Configuration File Extensions

   In RELOAD, peers receive a configuration document at bootstrap time.
   ALM parameter definitions for the configuration file will be defined
   in a later version.





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13.  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 Peercasting Example.


14.  Open Issues

   o  The specific capabilities of clients in terms of tree creation and
      being parents of other nodes will be described in subsequent
      versions.

   o  ALM parameter definitions for the RELOAD configuration file will
      be defined in a later version.

   o  Should any other ALM algorithms be mapped

   o


15.  IANA Considerations

   This memo includes no request to IANA.

   Code points for the kinds defined in this document MUST not conflict
   with any defined code points for RELOAD.  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 will be
   defined in the private use range.

   Code points for new message types defined in this document must not
   conflict with any defined code points for RELOAD.  Unlike Data Kind-
   IDs which permit private code points, RELOAD does not define private
   or experimental code points for Message Codes.  For experimental
   purposes we recommend using message code points in the range 0x7000
   to 0x70FF for the new message types defined in this specification:

   All ALM Usage messages support the RELOAD Message Extension
   mechanism.








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                  +-----------------------+------------+
                  | Message               | Code Point |
                  +-----------------------+------------+
                  | CreateALMTree         | 0x7000     |
                  | CreateALMTreeResponse | 0x7001     |
                  | Join                  | 0x7002     |
                  | JoinAccept            | 0x7003     |
                  | JoinConfirm           | 0x7004     |
                  | JoinDecline           | 0x7005     |
                  | Leave                 | 0x7006     |
                  | LeaveResponse         | 0x7007     |
                  | Reform                | 0x7008     |
                  | ReformResponse        | 0x7009     |
                  | Heartbeat             | 0x700A     |
                  | Push                  | 0x700B     |
                  | PushResponse          | 0x700C     |
                  +-----------------------+------------+

                            Message Code Points

   No new Error Codes are defined.

   Application-ID: The ALM Usage Application-IDs must not conflict with
   other applications of reload.  Additionally if AppAttach is used, the
   port number must be selected to avoid conflicts.

   Access Control Policies: No new policies.

   ALM Algorithm Types: There is currently one type: SCRIBE-RELOAD.


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 NodeId

   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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   o


17.  References

17.1.  Normative References

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

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

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
              "Internet Group Management Protocol (IGMP) / Multicast
              Listener Discovery (MLD)-Based Multicast Forwarding
              ("IGMP/MLD Proxying")", RFC 4605, August 2006.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.

   [RFC5058]  Boivie, R., Feldman, N., Imai, Y., Livens, W., and D.
              Ooms, "Explicit Multicast (Xcast) Concepts and Options",
              RFC 5058, November 2007.

17.2.  Informative References

   [AGU1984]  Aguilar, L., "Datagram Routing for Internet Multicasting",
              ACM Sigcomm 84 1984, March 1984,
              <http://dl.acm.org/citation.cfm?id=802060>.

   [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.,



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              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>.

   [HE2005]   He, Q. and M. Ammar, "Dynamic Host-Group/Multi-Destination
              Routing for Multicast Sessions", J. Telecommunication
              Systems vol. 28, pp. 409-433, 2005, <http://
              ieeexplore.ieee.org/xpl/
              freeabs_all.jsp?arnumber=1284204&abstractAccess=no&
              userType=inst>.

   [I-D.ietf-mboned-auto-multicast]
              Bumgardner, G. and T. Morin, "Automatic Multicast
              Tunneling", draft-ietf-mboned-auto-multicast-12 (work in
              progress), February 2012.

   [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-21 (work in
              progress), March 2012.

   [I-D.ietf-p2psip-sip]
              Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
              H. Schulzrinne, "A SIP Usage for RELOAD",
              draft-ietf-p2psip-sip-07 (work in progress), January 2012.

   [I-D.irtf-p2prg-rtc-security]
              Schulzrinne, H., Marocco, E., and E. Ivov, "Security
              Issues and Solutions in Peer-to-peer Systems for Realtime
              Communications", draft-irtf-p2prg-rtc-security-05 (work in
              progress), September 2009.

   [I-D.irtf-sam-hybrid-overlay-framework]
              Buford, J., "Hybrid Overlay Multicast Framework",
              draft-irtf-sam-hybrid-overlay-framework-02 (work in
              progress), February 2008.

   [I-D.irtf-samrg-common-api]
              Waehlisch, M., Venaas, S., and T. Schmidt, "A Common API
              for Transparent Hybrid Multicast",
              draft-irtf-samrg-common-api-04 (work in progress),
              January 2012.

   [I-D.matuszewski-p2psip-security-overview]
              Yongchao, S., Matuszewski, M., and D. York, "P2PSIP



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              Security Overview and Risk Analysis",
              draft-matuszewski-p2psip-security-overview-01 (work in
              progress), October 2009.

   [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>.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, August 1989.

   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,
              selection, and registration of an Autonomous System (AS)",
              BCP 6, RFC 1930, March 1996.

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

   [RFC4286]  Haberman, B. and J. Martin, "Multicast Router Discovery",
              RFC 4286, December 2005.

   [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>.


Appendix A.  Additional Stuff

   This becomes an Appendix.


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


   Thomas C. Schmidt
   HAW Hamburg
   Berliner Tor 7
   Hamburg,   20099
   Germany

   Email: schmidt@informatik.haw-hamburg.de
   URI:   http://inet.cpt.haw-hamburg.de/members/schmidt


   Matthias Waehlisch
   link-lab & FU Berlin
   Hoenower Str. 35
   Berlin  10318
   Germany

   Email: mw@link-lab.net























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