Requirements for Multicast Protocols
RFC 1458

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Network Working Group                                        R. Braudes
Request for Comments: 1458                                    S. Zabele
                                                                   TASC
                                                               May 1993

                  Requirements for Multicast Protocols

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Summary

   Multicast protocols have been developed over the past several years
   to address issues of group communication.  Experience has
   demonstrated that current protocols do not address all of the
   requirements of multicast applications.  This memo discusses some of
   these unresolved issues, and provides a high-level design for a new
   multicast transport protocol, group address and membership authority,
   and modifications to existing routing protocols.

Table of Contents

   1.    Introduction  . . . . . . . . . . . . . . . . . . . . . . .   2
   2.    The Image Communication Problem   . . . . . . . . . . . . .   2
   2.1   Scope   . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.2   Requirements  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.    Review of Existing Multicast Protocols  . . . . . . . . . .   4
   3.1   IP/Multicast  . . . . . . . . . . . . . . . . . . . . . . .   4
   3.2   XTP   . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.3   ST-II   . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.4   MTP   . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.5   Summary   . . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.    Reliable Adaptive Multicast Service   . . . . . . . . . . .   9
   4.1   The Multicast Group Authority   . . . . . . . . . . . . . .   9
   4.1.1 Address Management  . . . . . . . . . . . . . . . . . . . .   9
   4.1.2 Service Registration, Requests, Release, and Group
         Membership Maintenance  . . . . . . . . . . . . . . . . . .  10
   4.2   The Reliable Adaptive Multicast Protocol (RAMP)   . . . . .  11
   4.2.1 Quality of Service Levels   . . . . . . . . . . . . . . . .  12
   4.2.2 Error Recovery  . . . . . . . . . . . . . . . . . . . . . .  12
   4.2.3 Flow Control  . . . . . . . . . . . . . . . . . . . . . . .  13
   4.3   Routing Support   . . . . . . . . . . . . . . . . . . . . .  14
   4.3.1 Path Set-up   . . . . . . . . . . . . . . . . . . . . . . .  14
   4.3.2 Path Tear-down  . . . . . . . . . . . . . . . . . . . . . .  15

Braudes & Zabele                                                [Page 1]
RFC 1458          Requirements for Multicast Protocols          May 1993

   4.3.3 Multicast Routing Based on Quality of Service   . . . . . .  15
   4.3.4 Quality of Service Based Packet Loss  . . . . . . . . . . .  15
   5.    Interactions Among the Components: An Example   . . . . . .  15
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Security Considerations   . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Multicast protocols have been developed to support group
   communications.  These protocols use a one-to-many paradigm for
   transmission, typically using class D Internet Protocol (IP)
   addresses to specify specific multicast groups.  While designing
   network services for reliable transmission of very large imagery as
   part of the DARPA-sponsored ImNet program, we have reviewed existing
   multicast protocols and have determined that none meet all of the
   requirements of image communications [3].  This RFC reviews the
   current state of multicast protocols, highlights the missing
   features, and motivates the design and development of an enhanced
   multicast protocol.

   First, the requirements for network services and underlying protocols
   related to image communications are presented.  Existing protocols
   are then reviewed, and an analysis of each protocol against the
   requirements is presented.  The analyses identify the need for a new
   multicast protocol.  Finally, the features of an ideal reliable
   multicast protocol that adapts to network congestion in the
   transmission of large data volumes are presented.  Additional network
   components needed to fully support the new protocol, including a
   Multicast Group Authority and modifications to existing routing
   protocols, are also introduced.

2.  The Image Communications Problem

2.1 Scope

   Image management and communications systems are evolving from film-
   based systems toward an all-digital environment where imagery is
   acquired, transmitted, analyzed, and stored using digital computer
   and communications technologies.  The throughput required for
   communicating large numbers of very large images is extremely large,