IP Header Compression
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Auteur(s) : M. Degermark
, B. Nordgren
, S. Pink
Classé sous : Tcp
RFC 2507 IP Header Compression February 1999
This method is essentially the differential encoding techniques of
Jacobson, described in [RFC-1144], the differences being the placement
of the compressed TCP header fields (see section 6), the use of the
O-flag, the use of the R-flag, and elimination of the C-flag. The
O-flag allows compression of the TCP header when the Timestamp option
is used and the Options fields changes with each header.
DELTA values (except for Reserved field and Options, Padding) MUST be
coded as in [RFC-1144]. A Reserved field value passed with the R-flag
MUST NOT update the context at compressor or decompressor.
7.12.2. Without differential encoding
Source Port NOCHANGE (DEF)
Destination Port NOCHANGE (DEF)
(all the rest) RANDOM
The Identification field in a preceding IPv4 header is RANDOM.
A packet with a TCP header compressed according to the above must be
indicated to be of type COMPRESSED_TCP_NODELTA. It uses the same CID
space as COMPRESSED_TCP packets, and the header MUST be saved as
context. The compressed header is described in section 6.
This packet type can be sent as the response to a header request
instead of sending a full header, can be used over links that reorder
packets, and can be sent instead of a full header when there are
changes that cannot be represented by a compressed header. A
sophisticated compressor can switch to sending only
COMPRESSED_TCP_NODELTA headers when the packet loss frequency is high.
Degermark, et. al. Standards Track [Page 32]