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SAM                                                    J. Buford, Avaya
Internet Draft                                      S. Kadadi, Motorola
Intended Status: Informational                           March 12, 2008
Expires: Sept 12, 2008





                           SAM Problem Statement
                  draft-irtf-sam-problem-statement-02.txt


Status of this Memo

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   This Internet-Draft will expire on August 18, 2008.

Copyright

   Copyright (C) The IETF Trust (2008).







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Abstract

   We describe the generally expected behavior of a scalable and
   adaptive multicast architecture, leaving further details to separate
   documents on requirements and the SAM design space. This document is
   a starting point for discussions of feasibility, priority, and
   deployability.

Conventions used in this document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

   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].

Table of Contents


   1. Introduction...................................................2
   2. Heterogeneous Multicast Infrastructure.........................3
      2.1. Varying Infrastructure by Network Region..................3
      2.2. Regional Transitions......................................4
   3. Quality of Service.............................................4
      3.1. Native QOS, No Native Multicast...........................4
      3.2. Other Combinations........................................5
   4. Mobility.......................................................5
      4.1. Multicast Service Selection...............................6
      4.2. Transitions between ALM and Native Multicast..............7
      4.3. Other Considerations......................................7
   5. Security Considerations........................................8
   6. Conclusions....................................................8
   7. IANA Considerations............................................8
   8. References.....................................................8
      8.1. Normative References......................................8
      8.2. Informative References....................................8
   Author's Addresses................................................9
   Full Copyright Statement..........................................9
   Intellectual Property.............................................9
   Acknowledgment...................................................10

1. Introduction

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


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   o  large group size

   o  large numbers of small groups

   o  rate of group membership change

   o  admission control for QoS

   o  use with network layer QoS mechanisms

   o  varying degrees of reliability

   o  trees connecting nodes over 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

   o  use of different control mechanisms and tree structure in
      different regions of network depending on native multicast
      support, network characteristics, and node behavior

   The following sections describe some adaptation scenarios.  After the
   base scenarios are elaborated, then scenarios for scalability and
   dynamic adaptation should be added.

2. Heterogeneous Multicast Infrastructure

2.1. Varying Infrastructure by Network Region

   Regions A, B, C are disjoint areas of the network with some type of
   native multicast support.  Region Z is all other areas of the network
   with no native multicast support.  Region Z may be partitioned by A,
   B, and/or C.

   A multicast connection between nodes in A, B, C, and Z is needed. In
   each region A, B, C, the respective native multicast mechanism is
   used.

   Multicast topology choices include:





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   o  Multicast applications see an end-to-end multicast application
      layer which is mapped to a native layer transparently in the
      regions that it is available. The overlay's group management
      mechansisms hold for all nodes, and are mapped transparently to
      the native layer mechanisms in the appropriate regions.  All nodes
      have addresses in the overlay.

   o  Multicast applications see an end-to-end native multicast, where
      nodes in region Z connect to native regions using tunnels. The
      native group management mechanisms hold for all nodes.

   Homogeneous sub-case: regions A, B, C may use the same native
   multicast protocol.

2.2. Regional Transitions

   A node in a new region D joins the multicast tree.  Region D has
   native support.

   What is the minimum number of nodes in a region needed for native
   support to be used in that part of the tree?

3. Quality of Service

3.1. Native QOS, No Native Multicast

   Each endpoint in the multicast tree specifies QOS constraints such as
   bandwidth, delay, and jitter for a given source.  Multicast join
   includes admission control step for the selected QOS mechanism. This
   means that the join decision combines both multicast tree
   considerations (eg., best metrics) and an admission control decision.
   Paths to different endpoints from a given source might have different
   QOS constraints.  A given multicast tree may mix QOS delivery and
   best effort delivery to different receivers.

   Available IP QOS mechanisms include Intserv, Diffserv, and MPLS.
   Assume all regions of network have interoperable native QOS
   mechanism.  Assume all receivers have homogenous capabilities.

   The topology of the overlay is not assumed to be isomorphic to
   available QOS paths.  The overlay must be sophisticated enough to
   determine what paths are available and arrange its tree construction
   and routing behaviour accordingly.

   In order to enforce QOS, a measurement mechanism is needed. The
   scalability of the measurement, feedback and policing mechanism is an



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   important issue.  RTP is such a measurement and feedback protocol for
   UDP.

   A source might adapt its bit rate and quality depending on feedback
   from receivers.  There might be graceful degradation mechanisms such
   as multi-description coding over different multicast paths.  This
   behavior is application dependent.

3.2. Other Combinations

   Heterogeneous QOS refers to either 1) portions of the network where
   no QOS mechanism exists at native level, or 2) receivers which have
   heterogeneous capabilities.

   These combinations need further elaboration.

   o  Native QOS with Regional Native Multicast

   o  Heterogeneous QOS, No Native Multicast

   o  Heterogeneous QOS, Regional Native Multicast

4. Mobility

   We assume mobile nodes use Mobile IP (MIP), and that regions of the
   network that mobile nodes operate in are MIP enabled. Any node in the
   multicast tree may be mobile, and we consider source node mobility as
   a special case.

   A mobile node's home address (HoA) is associated with its overlay
   address (if this is an overlay) or group multicast address.   As the
   node moves to another network, multicast messages are routed to it
   via the home agent (HA).  In addition to increased latency, node
   mobility can impact robustness of multicast delivery due to loss of
   connectivity during mobility transitions. Some link layer solutions
   may mitigate or eliminate connectivity loss, but may require sending
   packets to both old and new care-of addresses during the transition.

   If the node uses its care-of address (CoA) in the overlay or
   multicast tree, then any mobility transition will be disruptive,
   causing a leave-join sequence.

   Forwarding of packets can be through the home agent.  If the source
   address is the care-of address, these might be rejected by nodes
   expecting packets only from overlay-registered addresses.




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   In general, mobile node transitions to another network lead to lost
   packets during the transition, and downstream nodes in the tree will
   also be disconnected.  Possibile solutions are bi-casting the packets
   to both old and new CoA, or buffering packets at the HA or old or new
   anchored points.

   If the overlay is aware that the node is mobile, then it could
   construct a mesh rather than tree to connect to.  The mesh might
   provide redundant paths to the mobile node's children in the tree.

   The overlay might use knowledge about node movement to make a set of
   target anchor points prejoin the multicast group/service so that the
   handoff delay can be reduced. Solutions similar to low latency
   handoffs/Fast MIPv6 (prereg) could be used.

   There can be different scenarios depending on whether all nodes in
   multicast tree are mobile or a subset of nodes.

4.1. Multicast Service Selection

   As the node moves from one network to another network, it can get
   multicast service in the new network in three ways: 1) from the new
   foreign network, 2) from the home network via a tunnel, 3) from the
   old foreign network via a tunnel, if the transition was from one
   foreign network to another.  The selection may depend on what is
   available in the new foreign network and which of the three
   mechanisms was used in the previous foreign network.

   1. Multicast service to/from the new foreign network

   o  In the case of native multicast, this means that the new foreign
      network has a multicast router which the mobile node uses. The
      mobile node can use the new IP address (obtained in the new
      network). This causes a leave-join sequence. If the router in the
      new network is not already a part the multicast tree, there will
      be additional delay to join the multicast tree in the foreign
      network. The mobile node uses either the CoA as the source address
      of control messages or its HoA.

   2. Multicast service via home network

   o  Multicast packets are tunneled to/from the mobile node by the HA.
      The mobile node uses HoA for multicast control messages. No need
      to join/leave the multicast group during handoff. The transmission
      path is not optimal.




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   o  If the tunnel end-point is not a mobile node, this may result in
      duplicate packets. Consider the case where packets of the same
      multicast group are tunneled to the new network. This means two
      HAs are tunneling packets for the same multicast group to the same
      foreign network. Possible solutions to this are: 1) applications
      in mobile node takes care of duplicate packets, 2) multicast
      packets are sent to mobile node as unicast packets (e.g., Mobile
      IPv4 uses this solution).

   3. Multicast service from old foreign network

   o  The mobile node gets the packets from its old multicast service
      anchor point until it registers/joins new multicast service anchor
      point in new network. Once it starts getting packets from new
      anchor point, it leaves its old anchor point. This means that
      packets are tunneled from the old foreign network until the mobile
      node gets multicast service from the new foreign network.

   o  There is minimal packet loss. There may be duplicate packets
      during the transition. A leave and join sequence results.

4.2. Transitions between ALM and Native Multicast

   Transitions of mobile nodes between heterogeneous multicast networks
   (say, from a native multicast region to OL/ALM multicast region or
   vice versa) need to be considered.

4.3. Other Considerations

   o  Multicast source mobility: Mobile source nodes may have more
      impact than other cases, and overlay tree/mesh may be reorganized
      when the multicast source moves to a new network.  There may be
      solutions specific to source node mobility that may not scale to
      mobile nodes in general.

   o  Scalability of advertisement mechanisms. Multicast advertisements
      are also multicast packets with well known multicast group address
      and port number. If mobile nodes which are in the foreign network
      want to know about multicast services in home network, these
      advertisement packets should be sent to foreign network. The home
      agent can tunnel packets to the foreign network, but it can
      increase the load on the HA.

   o  Network topology supported by the access network.





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5. Security Considerations

   [RESC2006] surveys the security issues specific to overlay networks
   which include:

   o  Correctness of routing due to malicious nodes acting individually
      or collectively

   o  Node impersonation due to lack of secure routing and identity

   o  Fairness enforcement since each node acts autonomously, it can
      chose to limit its resource contribution to the operation of the
      overlay

   o  Denial of service (DOS)

   o  Using overlays for launching DDoS attacks [ROSS2006]

   SAM will not solve the overlay security problems, but should work
   with overlays that provide security mechanisms.

6. Conclusions

   Using this discussion with the separately developed SAM Design Space,
   we will be able to enumerate those ares of the problem space for
   which solutions exist and those which are open problems.  This will
   suggest the steps by which the SAM Framework [BUF2008] is designed.

7. IANA Considerations

   This document has no actions for IANA.

8. References

8.1. Normative References

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

8.2. Informative References

   [MUR2006] E. Muramoto, Y. Imai, N. Kawaguchi. Requirements for
             Scalable Adaptive Multicast Framework in Non-GIG Networks.
             November 2006.  Internet Draft draft-muramoto-irtf-sam-
             generic-require-01.txt, work in progress.




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   [RESC2006] E. Rescorla.  Introduction to Distributed Hash Tables.
             IETF-65 Technical Plenary, March 2006.
             www3.ietf.org/proceedings/06mar/slides/plenaryt-2.pdf

   [ROSS2006] K. Ross.  Exploiting P2P Systems for DDOS Attacks.  IETF
             65 P2PRG CORE Subgroup.  www.cs.uml.edu/~buford/irtf-
             p2prg/ietf65/ietf65-irtf-p2prg-core-ddos.pdf

   [BUF2008] J. Buford. Hybrid Overlay Multicast Framework. IRTF SAM RG.
             draft-irtf-sam-hybrid-overlay-framework-02. March 2008,
             Work in Progress.

Author's Addresses

   John Buford
   Avaya Labs
   307 Middletown-Lincroft Road, 1J 243
   Lincroft, NJ 07738
   USA
   Email: buford at samrg dot org

   Shivanand Kadadi
   Motorola Bangalore India
   Email: a22063@motorola.com

Full Copyright Statement

   Copyright (C) The IETF Trust (2008).
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Intellectual Property

   The IETF takes no position regarding the validity or scope of any
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   pertain to the implementation or use of the technology described in


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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).

























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