Explicit Multicast (Xcast) Concepts and Options
RFC 5058

Document Type RFC - Experimental (November 2007; Errata)
Last updated 2013-03-02
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IESG IESG state RFC 5058 (Experimental)
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Send notices to rhboivie@us.ibm.com
Network Working Group                                          R. Boivie
Request for Comments: 5058                                    N. Feldman
Category: Experimental                                               IBM
                                                                 Y. Imai
                                                          WIDE / Fujitsu
                                                               W. Livens
                                                                  ESCAUX
                                                                 D. Ooms
                                                              OneSparrow
                                                           November 2007

            Explicit Multicast (Xcast) Concepts and Options

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

Abstract

   While traditional IP multicast schemes (RFC 1112) are scalable for
   very large multicast groups, they have scalability issues with a very
   large number of distinct multicast groups.  This document describes
   Xcast (Explicit Multi-unicast), a new multicast scheme with
   complementary scaling properties: Xcast supports a very large number
   of small multicast sessions.  Xcast achieves this by explicitly
   encoding the list of destinations in the data packets, instead of
   using a multicast group address.

   This document discusses Xcast concepts and options in several areas;
   it does not provide a complete technical specification.

Boivie, et al.                Experimental                      [Page 1]
RFC 5058               Xcast Concepts and Options          November 2007

Table of Contents

   1. Introduction ....................................................3
   2. Xcast Overview ..................................................4
   3. The Cost of the Traditional IP Multicast Schemes ................6
   4. Motivation ......................................................9
   5. Application ....................................................11
   6. Xcast Flexibility ..............................................12
   7. Xcast Control Plane Options ....................................13
      7.1. SIP Control Plane for Xcast ...............................14
      7.2. Receiver-Initiated Join for Xcast .........................14
   8. Optional Information ...........................................15
      8.1. List of Ports .............................................15
      8.2. List of DSCPs .............................................15
      8.3. Channel Identifier ........................................15
   9. Possible Xcast Packet Encoding .................................16
      9.1. General ...................................................16
      9.2. IPv4 ......................................................17
           9.2.1. IPv4 Header ........................................17
           9.2.2. Xcast4 Header ......................................17
      9.3. IPv6 ......................................................20
           9.3.1. IPv6 Header ........................................20
           9.3.2. Xcast6 Header ......................................20
                  9.3.2.1. Routing Extension Header ..................21
                  9.3.2.2. Destination Extension Header ..............21
   10. Impact on Upper-Layer Protocols ...............................22
      10.1. Checksum Calculation in Transport-Layer Headers ..........22
      10.2. IPsec ....................................................22
   11. Gradual Deployment ............................................23
      11.1. Tunneling ................................................23
      11.2. Premature X2U ............................................25
      11.3. Semi-Permeable Tunneling (IPv6 Only) .....................25
      11.4. Special Case: Deployment without Network Support .........26
      11.5. Using a Small Number of Xcast-Aware Routers to
            Provide Xcast ............................................27
   12. (Socket) API ..................................................28
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