Network Working Group                                 P. Newman, Ipsilon
Request for Comments: 1954                         W. L. Edwards, Sprint
Category: Informational                               R. Hinden, Ipsilon
                                                     E. Hoffman, Ipsilon
                                                  F. Ching Liaw, Ipsilon
                                                        T. Lyon, Ipsilon
                                                    G. Minshall, Ipsilon
                                                                May 1996


          Transmission of Flow Labelled IPv4 on ATM Data Links
                          Ipsilon Version 1.0

Status of this Memo

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

IESG Note:

   This note documents a private protocol for IPv4-based flows.  This
   protocol is NOT the product of an IETF working group nor is it a
   standards track document. It has not necessarily benefited from the
   widespread and in depth community review that standards track
   documents receive.

Abstract

   This document specifies the manner for transmitting IPv4 datagrams
   over an ATM data link, both in a default manner and in the presence
   of flow labelling via Ipsilon Flow Management Protocol [IFMP].

Table of Contents

   Introduction....................................................2
   1. Labels.......................................................2
   2. Default Encapsulation........................................2
   3. Flow Type 0 Encapsulation....................................3
   4. Flow Type 1 Encapsulation....................................4
   5. Flow Type 2 Encapsulation....................................5
   References......................................................7
   Security Considerations.........................................7
   Authors' Addresses..............................................7







Newman, et. al.              Informational                      [Page 1]
 
RFC 1954               Flow Labelled IPv4 on ATM                May 1996


Introduction

   This document specifies the manner for transmitting IPv4 datagrams
   over an ATM data link, both in a default manner and in the presence
   of flow labelling via Ipsilon Flow Management Protocol [IFMP].  ATM
   specific functions such as OAM cells, the CLP bit, and ABR RM cells
   are not used.  There are no reserved VCIs other than VPI = 0, VCI =
   0, which indicates an unassigned cell; and VPI = 0, VCI = 15, which
   is used for the default encapsulation.  IFMP messages must be sent
   using the default encapsulation.

. Labels

   Labels, as carried by IFMP, are realized on an ATM data link as
   specific VPI/VCIs.  The format of the Label field for ATM labels is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Reservd|          VPI          |             VCI               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The low order 16 bits of the label correspond to the VCI, with the
   least significant bit of the Label field corresponding to the least
   significant bit of the VCI.  If the link cannot support a full 16 bit
   VCI the unused bits of the VCI must be the most significant bits and
   they must be set to zero.

   The next 12 higher order bits of the label correspond to the VPI,
   with the least significant of these bits corresponding to the least
   significant bit of the VPI.  If the link cannot support a full 12 bit
   VPI, then the unused bits of the VPI must be the most significant
   bits and they must be set to zero.  The most significant four bits of
   the label are reserved.  They should be set to zero by the sender and
   ignored by the receiver.

. Default Encapsulation

   The default encapsulation for IPv4 packets on ATM data links is the
   LLC/SNAP encapsulation specified in section 4.1 "LLC encapsulation
   for routed protocols" of RFC 1483 [RFC1483].  Such frames begin with
   the octets 0xAA 0xAA 0x03 0x00 0x00 0x00 0x08 0x00 (the LLC/SNAP
   header for IPv4).  The LLC/SNAP header is prefixed to the IP datagram
   and the entire packet is encapsulated within the payload of an AAL-5
   CPCS-PDU as specified in RFC 1483 and illustrated below:






Newman, et. al.              Informational                      [Page 2]
 
RFC 1954               Flow Labelled IPv4 on ATM                May 1996


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               LLC (0xAA-AA-03)                |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
   |                   SNAP (0x00-00-00-08-00)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         IPv4 Datagram                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Pad (0 - 47 octets)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +               AAL-5 CPCS-PDU Trailer (8 octets)               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The maximum transmission unit (MTU) of an IPv4 datagram using the
   default encapsulation is 1500 octets.

   Frames using the default encapsulation are sent to: VPI = 0, VCI =
   15.

. Flow Type 0 Encapsulation

   All