Transmission of Flow Labelled IPv4 on ATM Data Links Ipsilon Version 1.0
RFC 1954

quot; 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:

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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].

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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

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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

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