Network Working Group S. Mathur
Request for Comments: 1553 M. Lewis
Category: Standards Track Telebit Corporation
Compressing IPX Headers Over WAN Media (CIPX)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state and
status of this protocol. Distribution of this memo is unlimited.
This document describes a method for compressing the headers of IPX
datagrams (CIPX). With this method, it is possible to
significantly improve performance over lower speed wide area
network (WAN) media. For normal IPX packet traffic, CIPX can
provide a compression ratio of approximately 2:1 including both IPX
header and data. This method can be used on various type of WAN
media, including those supporting PPP and X.25.
This memo ia a product of the Point-to-Point Protocol Extensions
(PPPEXT) Working Group of the IETF. Comments should be sent to
the authors and the email@example.com mailing list.
Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
This word, or the adjective "required", means that the
definition is an absolute requirement of the specification.
This phrase means that the definition is an absolute
prohibition of the specification.
Mathur & Lewis [Page 1]RFC 1553 CIPX December 1993
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
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.
Internetwork Packet Exchange (IPX) is a protocol defined by the
Novell Corporation . 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  for TCP/IP
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
Mathur & Lewis [Page 2]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
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