Avaya Configuring Data Compression Services Manuel d'utilisateur télécharger pdf (Page 35)

Data Compression Overview

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PPP Hi/fn LZS Compression Protocol

PPP uses CCP to negotiate how the router uses the Hi/fn LZS Compression

Protocol (RFC 1974). Specifically, CCP negotiates the different compression

modes that RFC 1974 supports. Bay Networks negotiates only mode 3 and the

number of compression histories, of which we support only one history.

RFC 1974 is specified only as an error detection protocol; unlike WCP, it does not

contain a transmit history. Instead, it relies on upper layer protocols to retransmit

data when errors occur.

For more information about compression protocol modes, refer to RFC 1974.

Data Compression Performance

The goals in using data compression are to achieve a high compression ratio while

maximizing throughput.

Compression ratio

is the size of uncompressed data

compared to the size of the same data after it is compressed.

Throughput

refers to

the amount of data that goes across the network in a specific amount of time. The

amount of throughput can indicate the efficiency and speed of the network.

The compression ratio varies according to the effectiveness of the compression

algorithm, but also according to the characteristics of the data you are

transmitting. Data that includes many redundant strings compresses at a high

ratio.

Throughput varies according to the number of devices in the network through

which the data must travel. Throughput is also affected by the compression and

decompression process.

Hardware Compression

Bay Networks hardware-based compression works with frame relay and PPP

networks. It best serves sites that support T1 or E1 lines, which often concentrate

many lower-speed remote connections. The hardware compression facility

operates at high speeds and also supports high-density WAN connections. Use

hardware compression when you want to achieve high compression ratios and

throughput, and also want to conserve router memory for other functions.

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 35