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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.

1. 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.

2. 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.

3. Flow Type 0 Encapsulation

   All IPv4 frames using Flow Type 0 are encapsulated within the payload
   of an AAL-5 CPCS-PDU.  This is the null encapsulation of section 5.1
   "VC based multiplexing of routed protocols" from RFC 1483 [RFC1483].
   There is no LLC/SNAP header.  The first octet of the frame
   corresponds to the first octet of the IPv4 datagram (i.e., the octet
   that contains the IP version number (4) and Internet Header Length
   (IHL) ).  The IP datagram is encapsulated within the payload of an
   AAL-5 CPCS-PDU as specified in RFC 1483 and illustrated below:

















Newman, et. al.              Informational                      [Page 3]

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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         IPv4 Datagram                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pad (0 - 47 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                AAL-5 CPCS-PDU Trailer (8 octets)              +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The MTU of an IPv4 datagram using Flow Type 0 encapsulation is 1500
   octets.

   Frames using Flow Type 0 encapsulation are sent to the VPI/VCI
   specified in the Label field of the corresponding IFMP Flow Type 0
   Redirect message element [IFMP].

4. Flow Type 1 Encapsulation

   All IPv4 frames using Flow Type 1 are encapsulated directly in the
   payload of an AAL-5 CPCS-PDU.  This is the null encapsulation of
   section 5.1 "VC based multiplexing of routed protocols" from RFC 1483
   [RFC1483].  There is no LLC/SNAP header.  Also, the following fields
   of the IP header are not transmitted: Version, Internet Header Length
   (IHL), Type of Service (TOS), Time to Live (TTL), Protocol, Source
   Address, and Destination Address.  In addition, the first 4 octets
   immediately following the IP header (as determined by the IHL field)
   are not transmitted.  (These 4 octets correspond to the source and
   destination ports for TCP and UDP datagrams.)  The value of the Total
   Length field is not changed; it remains the total length of the IP
   datagram before the above fields were removed.  The transmitted value
   of the Checksum field is the checksum value that would have been
   computed for the entire IP header if the TTL field had been set to
   zero (i.e., the actual value of the TTL field is "subtracted", using
   one's-complement arithmetic, from the Checksum before transmission).

   The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
   PDU as specified in RFC 1483 and illustrated below:









Newman, et. al.              Informational                      [Page 4]

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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Total Length          |        Identification         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Flags|     Fragment Offset     |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                             Data                              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pad (0 - 47 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                AAL-5 CPCS-PDU Trailer (8 octets)              +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The MTU of the IPv4 datagram using Flow Type 1 encapsulation is 1484
   octets (1500 octets minus the 16 octets specified above).

   Frames using Flow Type 1 encapsulation are sent to the VPI/VCI
   specified in the Label field of the corresponding IFMP Flow Type 1
   redirect message element [IFMP].

5. Flow Type 2 Encapsulation

   All IPv4 frames using Flow Type 2 are encapsulated directly in the
   payload of an AAL-5 CPCS-PDU.  This is the null encapsulation of
   section 5.1 "VC based multiplexing of routed protocols" from RFC 1483
   [RFC1483].  There is no LLC/SNAP header.  Also, the following fields
   of the IP header are not transmitted: Version, Internet Header Length
   (IHL), Time to Live (TTL), Source Address, and Destination Address.
   The first 4 octets immediately following the IP header (as determined
   by the IHL field) are transmitted.  (These 4 octets correspond to the
   source and destination ports for TCP and UDP datagrams.) The value of
   the Total Length field is not changed; it remains the total length of
   the IP datagram before the above fields were removed.  The
   transmitted value of the Checksum field is the checksum value that
   would have been computed for the entire IP header if the TTL field
   had been set to zero (i.e., the actual value of the TTL field is
   "subtracted", using one's-complement arithmetic, from the Checksum
   before transmission).

   The IP datagram is encapsulated within the payload of an AAL-5 CPCS-
   PDU as specified in RFC 1483 and illustrated below:





Newman, et. al.              Informational                      [Page 5]

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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |Type of Service|         Total Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Identification         |Flags|     Fragment Offset     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |   Protocol    |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                             Data                              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Pad (0 - 47 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                AAL-5 CPCS-PDU Trailer (8 octets)              +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Reserved fields are not used and should be set to zero by the
   sender and ignored by the receiver.

   The MTU of the IPv4 datagram using Flow Type 2 encapsulation is 1492
   octets (1500 octets minus the 8 octets specified above).

   Frames using Flow Type 2 encapsulation are sent to the VPI/VCI
   specified in the Label field of the corresponding IFMP Flow Type 2
   redirect message element [IFMP].






















Newman, et. al.              Informational                      [Page 6]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


References

      [IFMP] Newman, P., et. al., "Ipsilon Flow Management Protocol
                Specification for IPv Version 1.0", Ipsilon Networks
                Inc., RFC 1953, May 1996.

      [RFC1483] Heinanen, J., "Multiprotocol Encapsulation over ATM
                Adaptation Layer 5", RFC 1483, July 1993.

SECURITY CONSIDERATIONS

   Security issues are not discussed in this document.

AUTHORS' ADDRESSES

   Peter Newman                        Phone: +1 (415) 846-4603
   Ipsilon Networks, Inc.              EMail: pn@ipsilon.com

   W. L. Edwards, Chief Scientist      Phone:  +1 (913) 534 5334
   Sprint                              EMail:  texas@sprintcorp.com

   Robert M. Hinden                    Phone: +1 (415) 846-4604
   Ipsilon Networks, Inc.              EMail: hinden@ipsilon.com

   Eric Hoffman                        Phone: +1 (415) 846-4610
   Ipsilon Networks, Inc.              EMail: hoffman@ipsilon.com

   Fong Ching Liaw                     Phone: +1 (415) 846-4607
   Ipsilon Networks, Inc.              EMail: fong@ipsilon.com

   Tom Lyon                            Phone: +1 (415) 846-4601
   Ipsilon Networks, Inc.              EMail: pugs@ipsilon.com

   Greg Minshall                       Phone: +1 (415) 846-4605
   Ipsilon Networks, Inc.              EMail: minshall@ipsilon.com
















Newman, et. al.              Informational                      [Page 7]

RFC 1954               Flow Labelled IPv4 on ATM                May 1996


Ipsilon Networks, Inc. is located at:

   2191 East Bayshore Road
   Suite 100
   Palo Alto, CA 94303
   USA

Sprint is located at:

   Sprint
   Sprint Technology Services - Long Distance Division
   9300 Metcalf Avenue
   Mailstop KSOPKB0802
   Overland Park, KS 66212-6333
   USA




































Newman, et. al.              Informational                      [Page 8]