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IEN-72 Multiplexing Protocol Jonathan B. Postel 23 January 1979 Information Sciences Institute University of Southern California 4676 Admiralty Way Marina del Rey, California 90291 (213) 822-1511 IEN-72 J. Postel ISI 23 January 1979 Multiplexing Protocol Introduction This Multiplexing Protocol is defined to allow the combining of transmission units of different higher level protocols in one transmission unit of a lower level protocol in packet-switched computer communication in the environment of an interconnected set of computer networks. This protocol assumes that the Internet Protocol [1] is used as the underlying protocol. Format 0 15 16 31 +--------+--------+----------------+ ! ! ! ! ! Zero !Protocol! Length ! ! ! ! ! +--------+--------+----------------+ Multiplexing Header Format Fields Zero is always zero. Protocol is the number of the following lower level protocol. Length is the length in octets of the following protocol block. Postel [page 1] 23 January 1979 Multiplexing Protocol IEN-72 Example Example 0 15 16 31 +--------+--------+--------+--------+ ! Zero !Protocol! Length ! +--------+--------+--------+--------+ ! a transmission unit ! ! of some protocol ! +--------+--------+--------+--------+ ! Zero !Protocol! Length ! +--------+--------+--------+--------+ ! a transmission unit ! ! of some protocol ! +--------+--------+--------+--------+ ! Zero !Protocol! Length ! +--------+--------+--------+--------+ ! a transmission unit ! ! of some protocol ! +--------+--------+--------+--------+ Multiplexing Protocol Concept [page 2] Postel 23 January 1979 IEN-72 Multiplexing Protocol Example 0 15 16 31 +--------+--------+--------+--------+ ! Zero !datagram! Length = 16 ! ----+ +--------+--------+--------+--------+ ! ! source socket ! dest. socket ! ! +--------+--------+--------+--------+ ! ! length = 8 ! checksum ! ! +--------+--------+--------+--------+ ! ! data ! ! +--------+--------+--------+--------+ ! ! data ! ! +--------+--------+--------+--------+ <---+ ! Zero ! TCP ! Length = 28 ! ----+ +--------+--------+--------+--------+ ! ! source port ! destination port! ! +--------+--------+--------+--------+ ! ! sequence number ! ! +--------+--------+--------+--------+ ! ! acknowledgment number ! ! +--------+--------+--------+--------+ ! !offset control! window ! ! +--------+--------+--------+--------+ ! ! checksum ! urgent pointer ! ! +--------+--------+--------+--------+ ! ! data ! ! +--------+--------+--------+--------+ ! ! data ! ! +--------+--------+--------+--------+ <---+ ! Zero !datagram! Length = 12 ! ----+ +--------+--------+--------+--------+ ! ! source socket ! dest. socket ! ! +--------+--------+--------+--------+ ! ! length = 4 ! checksum ! ! +--------+--------+--------+--------+ ! ! data ! ! +--------+--------+--------+--------+ <---+ Multiplexing Protocol Example Protocol Application The major use of this protocol is to allow several transmission units from differing (or the same) higher level protocols to be combined into one transmission unit of a lower level protocol. Postel [page 3] 23 January 1979 Multiplexing Protocol IEN-72 Protocol Number Protocol Number This is protocol 18 (22 octal) when used in the Internet Protocol. Other protocol numbers are listed in [2]. [page 4] Postel 23 January 1979 IEN-72 Multiplexing Protocol References References [1] Postel, J., "Internetwork Protocol Specification -- Version 4," IEN-54, USC-Information Sciences Institute, September 1978. [2] Postel, J., "Assigned Numbers," USC-Information Sciences Institute, RFC-750, NIC-45500, September 1978. Postel [page 5]