Internet Engineering Task Force                              R. Lehtonen
Internet-Draft                                               TeliaSonera
Expires: August 15, 2005                                       S. Venaas
                                               University of Southampton
                                                               M. Hoerdt
                                        University Louis Pasteur - LSIIT
                                                            Feb 11, 2005

           Requirements for discovery of dynamic SSM sources

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   Copyright (C) The Internet Society (2005).


   This draft identifies the need for discovering new SSM sources in a
   multicast session.  It also defines the basic requirements for such

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  5
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1   General requirements . . . . . . . . . . . . . . . . . . .  5
     4.2   Host requirements  . . . . . . . . . . . . . . . . . . . .  5
     4.3   Signalling requirements  . . . . . . . . . . . . . . . . .  6
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     8.1   Normative References . . . . . . . . . . . . . . . . . . .  7
     8.2   Informative References . . . . . . . . . . . . . . . . . .  8
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  8
       Intellectual Property and Copyright Statements . . . . . . . . 10

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1.  Introduction

   Many multi-party applications make use of multicast.  Multicast
   offers obvious benefits when one party is sending the same content to
   multiple receivers.  Also traditional multicast [3] allows for a
   multi-party session to be identified by a single group address.

   Any participant can send to the group without knowing who the
   receivers are, and all receivers can join the group without knowing
   who will send.  This means for e.g.  a video conference, one only
   needs to give the multicast group address to potential participants,
   possibly making a public announcement.  Participants can then come
   and go as they like, and those that happen to be sending to or
   receiving from the group address simultaneously will be able to reach
   each other.

   There are several problems with traditional multicast [6] and it's
   widely believed that Source-Specific Multicast (SSM) [1] is a more
   scalable and easier to deploy interdomain multicast technology in the
   long term.  One of the simplifications of SSM is that source
   discovery is not done in the network.  It's however precisely the
   network source discovery (typically using MSDP and Rendezvous-points)
   that allows anyone to start sending at any point and the receivers to
   get the data without knowing who the sources are.

   SSM requires the application to specify exactly which sources it will
   receive data from.  The source addresses must somehow be learned by
   the receivers out-of-band.  With traditional multicast the multicast
   group to use must be announced out-of-band before the session is to
   take place.  It may be announced using e.g.  SDP over HTTP or SAP.
   For SSM one could also list the addresses of the sources.  This works
   well where all the sources (participants) are known in advance, but
   this will often not be the case.  Also when announcing a multi-party
   session publicly and allowing anyone to join, there should be a
   simple mechanism for registering a participant and getting it
   announced to the others.  This draft defines the basic requirements
   for such functionality.

2.  Problem Statement

   As illustrated in the table 1, various multicast applications
   requirements may require different degree of dynamics in the source
   discovery process.  Existing and future applications require an out
   of band multicast source discovery mechanism which ideally offers the
   same level of performances than the current ASM architecture is
   offering now by in-band means.  Distributed Interactive Simulation
   (D.I.S) [4] is a good example of applications which require a very
   high level of performance from multicast source discovery.

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     |Applications type|Potential transient degree  |Current solution for|
     |                 |of the sources              |for source discovery|
     |Games, D.I.S     |High (measured in seconds)  |ASM or client-server|
     |Distributed      |High                        |client-server       |
     |File Sharing     |                            |                    |
     |Conferencing     |Medium (measured in minutes)|ASM or client-server|
     |TV/Radio         |Low    (measured in days)   |Static publishing   |

   Table 1 : Transient degree of various potential multicast

   Today most of the multi-party applications containing transient
   source of data are client-server based and do not take advantage of
   IP multicast for source discovery.  This limits their efficiency and

   Operational experience and analysis [2] have shown that current ASM
   model implemented with MSDP [5] for source discovery has severe
   scaling and security problems in inter-domain scale.  In addition to
   MSDP there are other problems with the RP based source discovery
   mechanisms like deployment of new mechanisms into routers, RP as the
   traffic congestion point and insufficient support for both IP

   SSM model provides good scaling and security properties and works for
   both IP versions, but does not provide direct support for source
   discovery.  a typical application that requires discovery of sources
   during the session is video conferencing.  The solution for discovery
   of new sources during the ongoing session should be standardized for
   several reasons:

   o  Clients from different origins/vendors may participate in the same
      multicast session.

   o  Without a standardized solution application writers may decide to
      solve this problem in different non-compatible ways.

   o  Source discovery must be manageable, so we need a standard that is
      stable and can be managed/monitored (e.g.  to prevent DoS attacks
      against the multicast infrastructure).

   In any cases this source discovery standard will facilitate the

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   multi-source multicast applications writers to produce new
   applications with less cost and wider compatibility across the
   Internet.  The multi-source multicast applications deployment effort
   can be improved by such a solution.

3.  Applicability Statement

   The source discovery mechanism and its requirements only need that
   the underlying network supports SSM natively end-to-end.  The source
   discovery mechanism is intended to work in both inter-domain and
   intra-domain cases.  The source discovery mechanism should provide
   required SSM channel information to receivers.  Other application
   specific discovery requirements are out-of-scope (e.g.  discovery of
   source bandwidth, supported codecs, identification, etc.).

4.  Requirements

   This section lists the requirements for discovery of dynamic SSM
   sources.  The requirements are separated into general, host and
   signalling parts.

4.1  General requirements

   1.  Solution must provide discovery of dynamic SSM sources during the
       session, offering a comparable level of performance to the
       current ASM architecture.

   2.  Solution shouldn't introduce additional requirements on the
       network (in addition to SSM support).

   3.  Solution must work in SSM address space.

   4.  Solution should be easily manageable and provide good security
       and control properties.

   5.  Solution should allow co-existence with other source discovery

   6.  Gradual deployment must be possible without affecting the
       operation of other SSM hosts.

   7.  Adding AAA and related functionalities (e.g.  source access
       control) must be possible.

4.2  Host requirements

   1.  Source discovery functionality must have at least three different

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        separatable elements; source, receiver and rendezvous elements.
        Sources are required to register themselves to discovery
        process.  Receivers are required to understand source discovery
        signalling.  Rendezvous function is needed between sources and
        receivers for matchmaking and control purposes, a common point
        source discovery signalling.

   2.  Multiple applications and users on the same host must be able to
        use the source discovery functionality.

   3.  A group of users must be able to set up their own rendezvous

   4.  Rendezvous functionality must be able to work in routers and/or
        in specific hosts if needed for redundancy, availability and
        control purposes.

   5.  Rendezvous function should be possible to implement in the SSM
        application itself.

   6.  Overhead of being rendezvous must not be too big in terms of
        processing power, memory or signalling traffic consumption.

   7.  It must be possible to add rendezvous fallback and load-sharing
        properties (these functions are not part of the basic
        requirement set).

   8.  Registering sources to discovery process must be as simple as

   9.  There shouldn't be additional hypothesis on the receivers than
        SSM already brings.

   10.  Discovery mechanism should provide enough information on the
        sources that non-active sources and respective SSM channels can
        be teared down by the receivers.

4.3  Signalling requirements

   1.  Source discovery signalling must be separated from the actual
       multicast traffic to achieve the following advantages:

       *  Allow path setup before actual traffic is sent (also initial
          multicast packet gets delivered to receivers).

       *  Allow multicast traffic patterns to be different from source
          discovery.  Sources might send at low or high rates

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          independent of signalling rate.  Also the source discovery
          signalling might be periodical but not necessarily the traffic

       *  While signalling may go via a central control point the
          multicast traffic should always take the optimal path (no
          traffic congestion point).

   2.  Signalling architecture must be robust.  Information about new
       sources must be distributed to receivers in less than 1 second.
       New receivers must get the complete source information in less
       than 15 seconds (worst case).

   3.  Discovery mechanism must support both IP versions.

   4.  Minimum amount of extra state in routers for source discovery.

   5.  Discovery should use multicast where possible, to reduce the
       overhead of hosting rendezvous function.

   6.  Standardized and available mechanisms and protocols should be
       used where appropriate.

   7.  Source discovery signalling should not necessarily be
       centralized, the rendezvous function may be distributed across
       the network to improve the robustness of the mechanism.

5.  Security Considerations

   This document specifies requirements for source discovery and
   introduces no new security threats.  Security is an important aspect
   when deciding on a solution.

6.  IANA Considerations

   This document has no actions for IANA.

7.  Acknowledgements

   Thanks to Jean-Jacques Pansiot and Pekka Savola for review and
   constructive comments.

8.  References

8.1  Normative References

   [1]  Bhattacharyya, S., "An Overview of Source-Specific Multicast

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        (SSM)", RFC 3569, July 2003.

8.2  Informative References

   [2]  Rajvaidya, P., Ramachandran, K. and K. Almeroth, "Detection and
        Deflection of DoS Attacks Against the Multicast Source Discovery
        Protocol", IEEE Infocom 2003.

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

   [4]  Pullen, J., Myjak, M. and C. Bouwens, "Limitations of Internet
        Protocol Suite for Distributed Simulation the Large Multicast
        Environment", RFC 2502, February 1999.

   [5]  Fenner, B. and D. Meyer, "Multicast Source Discovery Protocol
        (MSDP)", RFC 3618, October 2003.

   [6]  Savola, P., "IPv6 Multicast Deployment Issues",
        Internet-Draft draft-ietf-mboned-ipv6-multicast-issues-01,
        September 2004.

Authors' Addresses

   Rami Lehtonen
   Hataanpaan valtatie 20
   Tampere 33100


   Stig Venaas
   University of Southampton
   School of Electronics and Computer Science
   Southampton, Hampshire SO17 1BJ
   United Kingdom


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   Mickael Hoerdt
   University Louis Pasteur - LSIIT
   C422 - Pole API - Boulevard Sebastien Brant
   67400 ILLKIRCH Cedex


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