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Configuring Data Compression Services

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Data Compression Architecture

Bay Networks uses the following algorithm and protocols to provide data

compression services:

• LZ-77 algorithm

• Compression Control Protocol (draft RFC)

• Bay Networks proprietary compression protocol (WCP)

LZ-77 Algorithm

We base our data compression 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.

Compression Control Protocol (CCP)

Bay Networks uses the draft RFC Compression Control Protocol (CCP) only to

enable or disable compression for PPP. CCP also includes a history reset request

and acknowledgment capability, but our implementation of data compression does

not use these features.

Bay Networks Compression (WCP)

Bay Networks data compression uses a proprietary transfer protocol (WCP) to

enable compression for Frame Relay and for X.25, and to transport compressed

packets for Frame Relay, X.25, and PPP. WCP negotiates compression mode,

history size, and buffer size. For Frame Relay and PPP WCP also retransmits

packets in the event of packet loss, and provides protection from inadvertent data

expansion (LAPB retransmits packets for X.25).

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 20