IP Multicast Applications: Challenges and Solutions
RFC 3170

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Network Working Group                                           B. Quinn
Request for Comments: 3170                                Celox Networks
Category: Informational                                      K. Almeroth
                                                        UC-Santa Barbara
                                                          September 2001

                       IP Multicast Applications:
                        Challenges and Solutions

Status of this Memo

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

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document describes the challenges involved with designing and
   implementing multicast applications.  It is an introductory guide for
   application developers that highlights the unique considerations of
   multicast applications as compared to unicast applications.

   To this end, the document presents a taxonomy of multicast
   application I/O models and examples of the services they can support.
   It then describes the service requirements of these multicast
   applications, and the recent and ongoing efforts to build protocol
   solutions to support these services.

Table of Contents

   1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.2 Focus and Scope. . . . . . . . . . . . . . . . . . . . . . . 3
   2. IP Multicast-enabled Network. . . . . . . . . . . . . . . . . . 3
     2.1 Essential Protocol Components. . . . . . . . . . . . . . . . 4
       2.1.1 Expedient Joins and Leaves . . . . . . . . . . . . . . . 5
       2.1.2 Send without a Join. . . . . . . . . . . . . . . . . . . 5
   3. IP Multicast Application Taxonomy . . . . . . . . . . . . . . . 6
     3.1 One-to-Many Applications . . . . . . . . . . . . . . . . . . 8
     3.2 Many-to-Many Applications. . . . . . . . . . . . . . . . . . 9
     3.3 Many-to-One Applications . . . . . . . . . . . . . . . . . .10
   4. Common Multicast Service Requirements . . . . . . . . . . . . .13
     4.1 Bandwidth Requirements . . . . . . . . . . . . . . . . . . .13

Quinn, et al.                Informational                      [Page 1]
RFC 3170               IP Multicast Applications          September 2001

     4.2 Delay Requirements . . . . . . . . . . . . . . . . . . . . .13
   5. Unique Multicast Service Requirements . . . . . . . . . . . . .14
     5.1 Address Management . . . . . . . . . . . . . . . . . . . . .16
     5.2 Session Management . . . . . . . . . . . . . . . . . . . . .16
     5.3 Heterogeneous Receiver Support . . . . . . . . . . . . . . .18
     5.4 Reliable Data Delivery . . . . . . . . . . . . . . . . . . .20
     5.5 Security . . . . . . . . . . . . . . . . . . . . . . . . . .21
     5.6 Synchronized Play-Out. . . . . . . . . . . . . . . . . . . .23
   6. Service APIs. . . . . . . . . . . . . . . . . . . . . . . . . .23
   7. Security Considerations . . . . . . . . . . . . . . . . . . . .24
   8. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . .24
   9. References. . . . . . . . . . . . . . . . . . . . . . . . . . .24
   10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .27
   11. Full Copyright Statement . . . . . . . . . . . . . . . . . . .28

1. Introduction

   IP Multicast will play a prominent role on the Internet in the coming
   years.  It is a requirement, not an option, if the Internet is going
   to scale.  Multicast allows application developers to add more
   functionality without significantly impacting the network.

   Developing multicast-enabled applications is ostensibly simple.
   Having datagram access allows any application to send to a multicast
   address.  A multicast application need only increase the Internet
   Protocol (IP) time-to-live (TTL) value to more than 1 (the default
   value) to allow outgoing datagrams to traverse routers.  To receive a
   multicast datagram, applications join the multicast group, which
   transparently generates an [IGMPv2, IGMPv3] group membership report.

   This apparent simplicity is deceptive, however.  Enabling multicast
   support in applications and protocols that can scale well on a
   heterogeneous network is a significant challenge.  Specifically,
   sending constant bit rate datastreams, reliable data delivery,
   security, and managing many-to-many communications all require
   special consideration.  Some solutions are available, but many of
   these services are still active research areas.

1.1 Motivation

   The purpose of this document is to provide a framework for
   understanding the challenges of designing and implementing multicast
   applications.  In order to use multicast communications correctly,
   application developers must first understand the various I/O models
   and the network services (in addition to basic multicast