Avaya Configuring Data Compression Services Manuel d'utilisateur télécharger pdf (Page 42)

Configuring Data Compression Services

4-6

Parameter: History Size

Default: 32 K for software compression; 8 K for hardware compression

Options: 32 K | 8 K

Function: Indicates the amount of memory allocated to compression history for the

line.

Remember that history size entails separate compression and

decompression histories and lookup tables on each side of a link. For

example, if the link uses software compression with a history of 8 KB,

each end of the link allocates 8 KB of memory for compression, 16 KB

for a compression lookup table, and 8 KB for decompression, or 32 KB

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

allocates 32 KB of memory for compression, 64 KB for a compression

lookup table, and 32 KB for decompression, for a total of 128 KB.

Hardware compression entails similar requirements.

Selecting 32 K for PPP WCP should not pose a problem, because PPP

allows only one circuit per line. Select 8 K or 32 K for Frame Relay and

X.25 lines, depending on the resources of your network. Remember that if

you are running Frame Relay in group mode, each interface in the group

maintains its own history size.

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

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

low available bandwidth.

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

than an 8 KB history.

If you select different history sizes for the two sides of a link, the smaller

of the two becomes the effective history size.

Instructions: Select either 32 K or 8 K.

MIB Object ID: 1.3.6.1.4.1.18.3.4.22.1.1.6

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 42