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PPP Stac LZS Compression Protocol
RFC 1974

Document type: RFC - Informational (August 1996; No errata)
Document stream: IETF
Last updated: 2013-03-02
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IESG State: RFC 1974 (Informational)
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Network Working Group                                          R. Friend
Request for Comments: 1974                              Stac Electronics
Category: Informational                                       W. Simpson
                                                              DayDreamer
                                                             August 1996

                   PPP Stac LZS Compression Protocol

Status of this Memo

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

Abstract

   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.

   The PPP Compression Control Protocol [2] provides a method to
   negotiate and utilize compression protocols over PPP encapsulated
   links.

   This document describes the use of the Stac LZS data compression
   algorithm, with single or multiple compression histories, for
   compressing PPP encapsulated packets.

Table of Contents

     1.     Introduction ..........................................    2
        1.1       Licensing .......................................    2
        1.2       Specification of Requirements ...................    3
     2.     LZS Packets ...........................................    3
        2.1       Padding .........................................    4
        2.2       Zero Deletion/Insertion .........................    4
        2.3       Reliability and Sequencing ......................    4
           2.3.1  Reset-Request and Reset-Ack Packet Formats.......    5
        2.4       Data Expansion ..................................    6
        2.5       Packet Format ...................................    6
           2.5.1  PPP Protocol ....................................    7
           2.5.2  History Number ..................................    7
           2.5.3  Check Value .....................................    7
              2.5.3.1  LCB ........................................    7
              2.5.3.2  CRC ........................................    7
              2.5.3.3  Sequence Number ............................    8
                 2.5.3.3.1  History Synchronization with Sequence
                             Numbers Example ......................    9

Friend & Simpson             Informational                      [Page 1]
RFC 1974                        Stac LZS                     August 1996

           2.5.4  History Synchronization Procedure ...............   10
           2.5.5  Compressed Data .................................   11
     3.     Sending Compressed Datagrams ..........................   12
        3.1       Transmitter Process .............................   12
        3.2       Receiver Process ................................   12
        3.3       History Maintenance .............................   13
        3.4       History Resynchronization Mechanism .............   14
     4.     Configuration Option Format ...........................   14
     5.     Definition of Extended Mode ...........................   16
        5.1       Extended Mode Packet Format .....................   16
        5.2       Extended Mode Transmitter Process ...............   18
        5.3       Extended Mode Receiver Process ..................   18
        5.4       Extended Mode Synchronization ...................   19
     SECURITY CONSIDERATIONS ......................................   19
     REFERENCES ...................................................   20
     CHAIR'S ADDRESS    ...........................................   20
     AUTHORS' ADDRESSES............................................   20

1.  Introduction

   Starting with a sliding window compression history, similar to LZ1
   [3], Stac Electronics developed a new, enhanced compression algorithm
   identified as Stac LZS.  The LZS algorithm is optimized to compress
   all file types as efficiently as possible.  Even string matches as
   short as two octets are effectively compressed.

   The Stac LZS compression algorithm supports both single compression
   history communication and multiple compression history communication.

   A single compression history will require the minimum amount of
   memory to implement, but may not provide as much compression as a
   multiple history implementation.

   Often, many streams of information are interleaved over the same
   link.  Each virtual link will transmit data that is independent of
   other virtual links.  Using multiple compression histories can
   improve the compression ratio of a communication link by associating
   separate compression histories with separate virtual links of
   communication.

1.1.  Licensing

[include full document text]