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 1996References      [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.comNewman, et. al.              Informational                      [Page 7]RFC 1954               Flow Labelled IPv4 on ATM                May 1996Ipsilon Networks, Inc. is located at:   2191 East Bayshore Road   Suite 100   Palo Alto, CA 94303   USASprint is located at:   Sprint   Sprint Technology Services - Long Distance Division   9300 Metcalf Avenue   Mailstop KSOPKB0802   Overland Park, KS 66212-6333   USANewman, et. al.              Informational                      [Page 8]