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PPP Gandalf FZA Compression Protocol
RFC 1993

Document type: RFC - Informational (August 1996)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

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IESG State: RFC 1993 (Informational)
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Network Working Group                                          A. Barbir
Request for Comments: 1993                                       Gandalf
Category: Informational                                          D. Carr
                                                               Newbridge
                                                              W. Simpson
                                                              DayDreamer
                                                             August 1996

                  PPP Gandalf FZA Compression Protocol

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  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 Gandalf FZA data compression
   algorithm [3] for compressing PPP encapsulated packets.

Table of Contents

     1.     Introduction ..........................................    1
        1.1       Licensing .......................................    1
     2.     FZA Packets ...........................................    2
        2.1       Packet Format ...................................    3
     3.     Configuration Option Format ...........................    4
     SECURITY CONSIDERATIONS ......................................    4
     ACKNOWLEDGEMENTS .............................................    5
     REFERENCES ...................................................    5
     CONTACTS .....................................................    5

Barbir, Carr & Simpson                                          [Page i]


RFC 1993                      Gandalf FZA                    August 1996

1.  Introduction

   FZA is a high performance LZ [4] derivative that maximizes
   compression at the expense of memory and CPU.  Compression
   performance can be adjusted based on CPU and memory available.

   Multiple PPP packets can be combined in a single compressed frame, or
   a single PPP packet can be spread across multiple frames.

1.1.  Licensing

   Source and object licenses are available on a non-discriminatory
   basis for either a royalty or fixed price arrangement.  Patent
   indemnity is included with the license.

Barbir, Carr & Simpson                                          [Page 1]
RFC 1993                      Gandalf FZA                    August 1996

2.  FZA Packets

   Before any FZA packets may be communicated, PPP must reach the
   Network-Layer Protocol phase.

   When the Compression Control Protocol (CCP) has reached the Opened
   state, and FZA is negotiated as the primary compression algorithm,
   the PPP Protocol field indicates type hex 00FB (link compressed
   datagram), or type hex 00FD (compressed datagram).

   The maximum length of the FZA datagram transmitted over a PPP link is
   the same as the maximum length of the Information field of a PPP
   encapsulated packet.

   Padding

      The FZA packets require the negotiation of the Self-Describing-
      Padding Configuration Option [5] at LCP Link Establishment.

   Reliability and Sequencing

      The FZA algorithm expects a reliable link, as described in "PPP
      Reliable Transmission" [6].

      FZA expects the packets to be delivered in sequence.

   Data Expansion

      The maximum expansion of Gandalf FZA is 2:1.  However, typical
      expansion on pre-compressed data is 1.01:1.  Expanded data is sent
      to maintain the integrity of the compression history.

      When the expansion exceeds the size of the peer's Maximum Receive
      Unit for the link, the expanded packet is sent in multiple PPP
      frames.  The compressed data contains an indication of the end of
      the original packet.

Barbir, Carr & Simpson                                          [Page 2]
RFC 1993                      Gandalf FZA                    August 1996

2.1.  Packet Format

   A summary of the Gandalf FZA packet format is shown below.  The
   fields are transmitted from left to right.

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         PPP Protocol          |     Compressed Data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   PPP Protocol

      One or two octets.  The PPP Protocol field is described in the
      Point-to-Point Protocol Encapsulation [1].

      Type 00FD is used when the PPP multilink protocol is not used,

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