RFC 1553 (rfc1553) - Page 2 of 23

Compressing IPX Headers Over WAN Media (CIPX)

RFC 1553                         CIPX                      December 1993


    SHOULD

      This word, or the adjective "recommended", means that there
      may exist valid reasons in particular circumstances to
      ignore this item, but the full implications should be
      understood and carefully weighed before choosing a
      different course.

    MAY

      This word, or the adjective "optional", means that this
      item is one of an allowed set of alternatives.  An
      implementation which does not include this option MUST be
      prepared to interoperate with another implementation which
      does include the option.

Introduction

   Internetwork Packet Exchange (IPX) is a protocol defined by the
   Novell Corporation [1].  It is derived from the Internet Datagram
   Protocol (IDP) protocol of the Xerox Network Systems (XNS) family
   of protocols.  IPX is a datagram, connectionless protocol that does
   not require an acknowledgment for each packet sent.  The IPX
   protocol corresponds to the network layer of the ISO model.

   Usually, there is a transport layer protocol above IPX.  The most
   common transport protocol is the Netware Core Protocol (NCP), which
   is used for file server access.  The Sequenced Packet Exchange
   (SPX) is the reliable connection-based transport protocol commonly
   used by applications.

   The IPX packet consists of a 30 octet IPX header, usually followed
   by the transport layer protocol header.  The NCP header is 6 octets
   in length.  The SPX header is 12 octets in length.

   Two strategies are described below for compressing IPX headers.
   This specification requires that implementations of CIPX support
   both IPX header compression strategies.  These header compression
   algorithms are based on those Van Jacobson described [2] for TCP/IP
   packets.
   The first strategy is to compress only the IPX header.  This
   compression algorithm can be used to compress any IPX packet,
   without affecting the transport protocol.  This algorithm
   compresses a 30 octet IPX header into a one to seven octet header.

   The second strategy is to compress the combined IPX and NCP
   headers.  This algorithm compresses only NCP packets with NCP type
   of 0x2222 and 0x3333.  This algorithm compresses a 36 octet NCP/IPX



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