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Data Compression Overview

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Data Compression Architecture

WCP and Hi/fn LZS use different compression algorithms and protocols. The

compression protocol that you choose depends on whether you are

communicating with routers from Nortel Networks or other vendors.

Table 2-1

lists the algorithms and protocols that Nortel Networks uses to provide

data compression services for WCP and Hi/fn LZS.

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

compression protocol:

• If both ends of the connection are Nortel Networks routers, configure both

routers to use WCP as the compression protocol.

• If the connection is a PPP link and only one end of the connection is a Nortel

Networks router, configure both routers to use Hi/fn LZS.

If you want the router to negotiate which protocol is used, use the BCC or Site

Manager to set the Compression Protocol parameter to Any (see page A-15

for the

parameter description).

LZ-77 Algorithm

Nortel 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 Hi/fn LZS

LZ-77 algorithm Hi/fn LZS algorithm

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

Nortel Networks proprietary WAN

Compression Protocol (WCP)

References the PPP Hi/fn LZS

Compression Protocol (RFC 1974) as a

guideline

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Avaya Configuring Data Compression Services Bedienungsanleitung Seite 37