Network Working Group                                 P. Newman, IpsilonRequest for Comments: 1954                         W. L. Edwards, SprintCategory: 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 1.0Status 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..............................................7Newman, et. al.              Informational                      [Page 1]RFC 1954               Flow Labelled IPv4 on ATM                May 1996Introduction   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]