Avaya Configuring Data Compression Services Manuel d'utilisateur télécharger pdf (Page 26)

Configuring Data Compression Services

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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.

32 KB History Size

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

You may 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 are available in 32 and 128 contexts. The

numbers 32 and 128 assume a history size of 8 KB per context, although you can

conﬁgure history size at either 8 KB or 32 KB. For example, if you conﬁgure

history size at 32 KB, you have used four 8 KB contexts, and you have that many

fewer contexts available to run hardware compression on your network.

Both boards reserve one 8 KB context for Packet-by-Packet, as opposed to

Continuous Packet compression. There is no limit to the number of VCs that can

use this one PPC context.

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 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 put strict limits on the number

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

size are the same for software and hardware compression.

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Avaya Configuring Data Compression Services Manuel d'utilisateur Page 26