IP Payload Compression Using LZS
RFC 2395

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Network Working Group                                        R. Friend
Request for Comments: 2395                                  R. Monsour
Category: Informational                                    Hi/fn, Inc.
                                                         December 1998

                    IP Payload Compression Using LZS

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes a compression method based on the LZS
   compression algorithm. This document defines the application of the
   LZS algorithm to the IP Payload Compression Protocol [IPCOMP].
   [IPCOMP] defines a method for applying lossless compression to the
   payloads of Internet Protocol datagrams.

Table of Contents

   1. Introduction...................................................2
      1.1 General....................................................2
      1.2 Background of LZS Compression..............................2
      1.3 Licensing..................................................3
      1.4 Specification of Requirements..............................3
   2. Compression Process............................................3
      2.1 Compression History........................................3
      2.2 Compression Encoding Format................................3
      2.3 Padding....................................................4
   3. Decompression Process..........................................4
   4. IPComp Association (IPCA) Parameters...........................4
      4.1 ISAKMP Transform ID........................................5
      4.2 ISAKMP Security Association Attributes.....................5
      4.3 Manual configuration.......................................5
      4.4 Minimum packet size threshold..............................5
      4.5 Compressibility test.......................................5
   5. Security Considerations........................................5
   6. Acknowledgements...............................................5
   7. References.....................................................6
   8. Authors' Addresses.............................................7

Friend & Monsour             Informational                      [Page 1]
RFC 2395            IP Payload Compression Using LZS       December 1998

   9. Appendix: Compression Efficiency versus Datagram Size..........8
   10. Full Copyright Statement......................................9

1. Introduction

1.1 General

   This document specifies the application of LZS compression, a
   lossless compression algorithm, to IP datagram payloads. This
   document is to be used in conjunction with the IP Payload Compression
   Protocol [IPCOMP].  This specification assumes a thorough
   understanding of the IPComp protocol.

1.2 Background of LZS Compression

   Starting with a sliding window compression history, similar to [LZ1],
   Hi/fn developed a new, enhanced compression algorithm identified as
   LZS. The LZS algorithm is a general purpose lossless compression
   algorithm for use with a wide variety of data types.  Its encoding
   method is very efficient, providing compression for strings as short
   as two octets in length.

   The LZS algorithm uses a sliding window of 2,048 bytes.  During
   compression, redundant sequences of data are replaced with tokens
   that represent those sequences. During decompression, the original
   sequences are substituted for the tokens in such a way that the
   original data is exactly recovered. LZS differs from lossy
   compression algorithms, such as those often used for video
   compression, that do not exactly reproduce the original data.

   The details of LZS compression can be found in [ANSI94].

   The efficiency of the LZS algorithm depends on the degree of
   redundancy in the original data.  A table of compression ratios for
   the [Calgary] Corpus file set is provided in the appendix in Section
   7.

Friend & Monsour             Informational                      [Page 2]
RFC 2395            IP Payload Compression Using LZS       December 1998

1.3 Licensing

   Hi/fn, Inc. holds patents on the LZS algorithm. Licenses for a
   reference implementation are available for use in IPPCP, IPSec, TLS
   and PPP applications at no cost.  Source and object licenses are
   available on a non-discriminatory basis. Hardware implementations are
   also available.  For more information, contact Hi/fn at the address
   listed with the authors' addresses.

1.4 Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC-2119].

2. Compression Process