Avaya Configuring Data Compression Services Manuel d'utilisateur télécharger pdf (Page 34)

Configuring Data Compression Services

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117352-D Rev. 00

Hi/fn LZS Algorithm

Hi/fn is a wholly owned subsidiary of Stac, Inc. Bay Networks Hi/fn LZS

compression software incorporates LZS from Hi/fn.

Bay Networks Hi/fn LZS compression software is based on the Hi/fn LZS

algorithm to transport compressed packets across a PPP link. Hi/fn LZS

implements an error detection mechanism, which means that it can detect whether

packets are lost during transmission. Hi/fn LZS does not retransmit packets if they

are lost.

The Hi/fn LZS compression algorithm searches incoming data for redundant data

strings and replaces these strings in the outgoing data with encoded tokens of

shorter length. Hi/fn LZS creates the encoded tokens from information in a table

that the Hi/fn LZS algorithm builds. This table consists of string matches, which

point to previous incoming data. As the table is built and tokens are created,

subsequent data is compressed based on previous data.

Compression Control Protocol (CCP)

Bay Networks uses RFC 1962, the Compression Control Protocol (CCP), to

enable or disable compression across a PPP link and determine what kind of

compression is used. CCP also includes a history reset request and

acknowledgment capability, which Hi/fn LZS uses but WCP does not. WCP uses

its own negotiation mechanism.

Bay Networks WAN Compression Protocol (WCP)

Bay Networks proprietary WAN Compression Protocol (WCP) is an IETF draft

standard. WCP enables compression for frame relay and for X.25, and transports

compressed packets for PPP, frame relay, and X.25. WCP negotiates compression

mode, history size, and buffer size. For PPP and frame relay, WCP also

retransmits packets in the event of packet loss and protects against inadvertent

data expansion (LAPB retransmits packets for X.25).

WCP is most effective for sites that have WAN connections operating at relatively

low speeds such as 56/64 KB, where you want to achieve data compression at low

cost and with minimal memory requirements. WCP supports connections up to

512 KB/s on the FRE-040. For networks operating at faster speeds, you should

use hardware compression.

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 34