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Data Compression Overview

117352-B Rev. 00

2-3

Data Compression Architecture

WCP and Stac LZS use different compression algorithms and protocols. The

compression protocol that you choose depends on whether you are

communicating with routers from Bay Networks or other vendors.

Table 2-1

lists the algorithms and protocols that Bay Networks uses to provide

data compression services for WCP and Stac LZS respectively:

You want to ensure that routers at both ends of the connection are using the same

compression protocol. You cannot have one router using WCP compression and

another router using Stac LZS compression.

If both ends of the connection are Bay Networks routers, use WCP as the

compression protocol. If the connection is a PPP link and only one end of the

connection is a Bay Networks router, use Stac LZS.

If you want the router to negotiate which protocol is used, set the Compression

Protocol parameter (refer to page A-10 for a parameter description).

LZ-77 Algorithm

Bay Networks WCP data compression software is based on a Lempel-Ziv (LZ-77)

algorithm. The algorithm uses a sliding history buffer that stores the data that the

network link has processed most recently. The compressor compares new data

strings with data it has already processed and stored in the buffer. When the

compressor detects data strings that match data it has already processed, it

replaces those strings with offset and length tokens that are shorter than the

original strings, thus compressing the data.

Table 2-1. Data Compression Algorithms and Protocols

WCP Stac LZS

LZ-77 algorithm Stac LZS algorithm

Compression Control Protocol (RFC 1962) Compression Control Protocol (RFC 1962)

Bay Networks proprietary compression

protocol (WCP)

References the PPP Stac LZS

Compression protocol (RFC 1974) as a

guideline

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 31