RFC 1553 (rfc1553) - Page 3 of 23

Compressing IPX Headers Over WAN Media (CIPX)

RFC 1553                         CIPX                      December 1993


   header into a one to eight octet header.

   Lastly, it is possible and many times desirable, to use this type
   of header compression in conjunction with some type of data
   compression.

   Data compression technology takes many forms. Link bit stream
   compression is a common approach over very low speed asynchronous
   links, normally performed by modems transparently.  Transparent bit
   stream compression is also offered in some DSUs, routers and
   bridges.  Data compression can be provided using protocols such as
   CCITT V.42bis[3], MNP 5, Lempel-Ziv, or LAPB[4].

   When using both header and data compression, the sequence of
   compression is important.  When sending packets, data compression
   MUST be done after header compression.  Conversely when receiving
   packets, data decompression MUST be done before header
   decompression.

IPX Compression Algorithm

   The normal IPX header consists of the following fields: checksum,
   packet length, transport control (hop count), packet type,
   destination and source address fields.

                             +-----------------------+
                             |       Checksum        |
                             +-----------------------+
                             |     Packet Length     |
                             +-----------+-----------+
                             |    Hops   |Packet Type|
                             +-----------+-----------+
                             |      Destination      |
                             |        Address        |
                             |      (12 Octets)      |
                             +-----------------------+
                             |        Source         |
                             |        Address        |
                             |      (12 Octets)      |
                             +-----------------------+

                                 IPX PACKET HEADER

   The IPX header diagram above is shown without the field alignment
   details.  Consider each field of the IPX header separately, and how
   it typically changes.

   Historically, Novell has not used the Checksum field in the IPX



Mathur & Lewis