Avaya Configuring Data Compression Services Uživatelský manuál stáhnout pdf (Strana 53)

Customizing Data Compression

117352-C Rev. 00

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8 KB History Size

In general, 8 KB histories are appropriate for frame relay and X.25, when you

have large numbers of VCs and need to conserve memory for each of them.

32 KB History Size

For PPP, with only one circuit per line, you may want to use a 32 KB history. You

may also want to allocate a 32 KB history size for links with speeds higher than 64

Kb/s to improve throughput. The compressor can find a data pattern match up to

three times faster using a 32 KB history than an 8 KB history.

History Size with Hardware Compression

Hardware compression daughterboards and net modules are available in 32, 128,

and 256 contexts. The numbers 32, 128, and 256 assume a history size of 8 KB

per context, although you can configure history size to either 8 KB or 32 KB. For

example, if you configure history size at 32 KB, you use four 8 KB contexts, and

you have that many fewer contexts available to run hardware compression on your

network.

Compression daughterboards reserve one 8 KB context for PPC, as opposed to

CPC. There is no limit to the number of VCs that can use this one PPC context.

The maximum number of VCs for the compression engine is 256.

The compression hardware uses memory in units called pages, where a page

equals 32 KB of memory. Each context that uses a 32 KB history uses one page of

memory. Restrictions for CPC contexts using either 8 or 32 KB histories are that

the memory used for any one history must be continuous, and that it may not cross

pages. For 8 KB contexts, these restrictions create few constraints, but for 32 KB

contexts, they are significant.

Note:

Although software compression does not place strict limits on the

number of contexts you can configure, be aware that memory requirements for

history size are the same for both software and hardware compression.

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Avaya Configuring Data Compression Services Uživatelský manuál Strana 53