RFC 2201 (rfc2201) - Page 1 of 15

Core Based Trees (CBT) Multicast Routing Architecture

Network Working Group                                       A. Ballardie
Request for Comments: 2201                                    Consultant
Category: Experimental                                    September 1997


         Core Based Trees (CBT) Multicast Routing Architecture

Status of this Memo

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

Abstract

   CBT is a multicast routing architecture that builds a single delivery
   tree per group which is shared by all of the group's senders and
   receivers.  Most multicast algorithms build one multicast tree per
   sender (subnetwork), the tree being rooted at the sender's
   subnetwork.  The primary advantage of the shared tree approach is
   that it typically offers more favourable scaling characteristics than
   all other multicast algorithms.

   The CBT protocol [1] is a network layer multicast routing protocol
   that builds and maintains a shared delivery tree for a multicast
   group.  The sending and receiving of multicast data by hosts on a
   subnetwork conforms to the traditional IP multicast service model
   [2].

   CBT is progressing through the IDMR working group of the IETF.  The
   CBT protocol is described in an accompanying document [1]. For this,
   and all IDMR-related documents, see http://www.cs.ucl.ac.uk/ietf/idmr

TABLE OF CONTENTS

   1. Background...................................................  2
   2. Introduction.................................................  2
   3. Source Based Tree Algorithms.................................  3
      3.1 Distance-Vector Multicast Algorithm......................  4
      3.2 Link State Multicast Algorithm...........................  5
      3.3 The Motivation for Shared Trees..........................  5
   4. CBT - The New Architecture...................................  7
      4.1 Design Requirements......................................  7
      4.2 Components & Functions...................................  8
          4.2.1 CBT Control Message Retransmission Strategy........ 10
          4.2.2 Non-Member Sending................................. 11
   5. Interoperability with Other Multicast Routing Protocols ..... 11



Ballardie                     Experimental