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Data Compression Overview

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PPP Stac LZS Compression Protocol

PPP uses CCP to negotiate how the router uses the Stac LZS, RFC 1974

compression protocol. 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 only specified as an error detection protocol, it does not contain a

transmit history like WCP. Instead, it relies on upper layer protocols for to

retransmit data when errors occur.

For more information on 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 a lot of redundant strings compresses at a high

ratio.

Throughput varies with the number of devices in the network that 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 T-1 or E-1 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 preserve router memory to perform other functions.

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Avaya Configuring Data Compression Services Manual de usuario Pagina 33