IP over ATM: A Framework Document
RFC 1932

Document Type RFC - Informational (April 1996; No errata)
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Network Working Group                                            R. Cole
Request for Comments: 1932                                       D. Shur
Category: Informational                           AT&T Bell Laboratories
                                                           C. Villamizar
                                                                     ANS
                                                              April 1996

                   IP over ATM: A Framework Document

Status of this Memo

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

   Abstract

   The discussions of the IP over ATM working group over the last
   several years have produced a diverse set of proposals, some of which
   are no longer under active consideration.  A categorization is
   provided for the purpose of focusing discussion on the various
   proposals for IP over ATM deemed of primary interest by the IP over
   ATM working group.  The intent of this framework is to help clarify
   the differences between proposals and identify common features in
   order to promote convergence to a smaller and more mutually
   compatible set of standards.  In summary, it is hoped that this
   document, in classifying ATM approaches and issues will help to focus
   the IP over ATM working group's direction.

1.  Introduction

   The IP over ATM Working Group of the Internet Engineering Task Force
   (IETF) is chartered to develop standards for routing and forwarding
   IP packets over ATM sub-networks.  This document provides a
   classification/taxonomy of IP over ATM options and issues and then
   describes various proposals in these terms.

   The remainder of this memorandum is organized as follows:

   o Section 2 defines several terms relating to networking and
     internetworking.

   o Section 3 discusses the parameters for a taxonomy of the
     different ATM models under discussion.

   o Section 4 discusses the options for low level encapsulation.

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RFC 1932           IP over ATM: A Framework Document          April 1996

   o Section 5 discusses tradeoffs between connection oriented and
     connectionless approaches.

   o Section 6 discusses the various means of providing direct
     connections across IP subnet boundaries.

   o Section 7 discusses the proposal to extend IP routing to better
     accommodate direct connections across IP subnet boundaries.

   o Section 8 identifies several prominent IP over ATM proposals that
     have been discussed within the IP over ATM Working Group and
     their relationship to the framework described in this document.

   o Section 9 addresses the relationship between the documents
     developed in the IP over ATM and related working groups and the
     various models discussed.

2.  Definitions and Terminology

   We define several terms:

   A Host or End System: A host delivers/receives IP packets to/from
     other systems, but does not relay IP packets.

   A Router or Intermediate System: A router delivers/receives IP
     packets to/from other systems, and relays IP packets among
     systems.

   IP Subnet: In an IP subnet, all members of the subnet are able to
      transmit packets to all other members of the subnet directly,
      without forwarding by intermediate entities.  No two subnet
      members are considered closer in the IP topology than any other.
      From an IP routing and IP forwarding standpoint a subnet is
      atomic, though there may be repeaters, hubs, bridges, or switches
      between the physical interfaces of subnet members.

   Bridged IP Subnet: A bridged IP subnet is one in which two or
      more physically disjoint media are made to appear as a single IP
      subnet.  There are two basic types of bridging, media access
      control (MAC) level, and proxy ARP (see section 6).

   A Broadcast Subnet: A broadcast network supports an arbitrary
      number of hosts and routers and additionally is capable of
      transmitting a single IP packet to all of these systems.

   A Multicast Capable Subnet: A multicast capable subnet supports
     a facility to send a packet which reaches a subset of the
     destinations on the subnet.  Multicast setup may be sender

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RFC 1932           IP over ATM: A Framework Document          April 1996

     initiated, or leaf initiated.  ATM UNI 3.0 [4] and UNI 3.1
     support only sender initiated while IP supports leaf initiated
     join.  UNI 4.0 will support leaf initiated join.

   A Non-Broadcast Multiple Access (NBMA) Subnet: An NBMA supports
     an arbitrary number of hosts and routers but does not
     natively support a convenient multi-destination connectionless
     transmission facility, as does a broadcast or multicast capable
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