Avaya Configuring Data Compression Services Manuel d'utilisateur télécharger pdf (Page 72)

Configuring Data Compression Services

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117352-D Rev. 00

Parameter: History Size

Path: Configuration Manager > Protocols > WCP > Interfaces

Default: Inherit from Line

Options: 32K

Inherit from Line

Function: Specifies the amount of memory allocated to compression history for the line.

Remember that history size has separate compression and decompression

histories and lookup tables on each side of a link. If the link uses a compression

history of 8 KB, each end of the link allocates a total of 32 KB as follows:

• 8 KB for compression

• 16 KB for a lookup table

• 8 KB for decompression

If the link uses a compression history of 32 KB, each end of the link allocates a

total of 128 KB as follows:

• 32 KB for compression

• 64 KB for a lookup table

• 32 KB for decompression

Hardware compression has similar requirements.

Selecting 32K for PPP WCP should not be a problem for the BN, because PPP

allows only one circuit per line. Select 8K or 32K for frame relay and X.25

circuits, depending on the resources of your network. Selecting 32K for PPP

WCP on the ASN can cause problems, particularly if you are using a 32-context

compression net module.

In general, 8 KB histories are appropriate for WAN links that run at speeds of

64 Kb/s or less, because less throughput is required. Use an 8 KB history size

with frame relay and X.25, which have large numbers of VCs and may have low

available bandwidth, and with PPP on a 32-context net module. You may want

to allocate a 32 KB history size for links with speeds higher than 64 Kb/s to

improve throughput. The compression engine can find a data pattern match up

to three times faster using a 32 KB history. If you select different history sizes

for each side of a link, the smaller of the two becomes the effective history size.

Inherit from Line allows you to set WCP parameters at the line level and apply

them to circuits.

Instructions: Select Inherit from Line if you want to accept the value in effect for the WCP

History Size line parameter. Otherwise, select either 32K or 8K.

MIB Object ID: 1.3.6.1.4.1.18.3.4.22.2.1.5

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 72