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Customizing Data Compression

114061 Rev. A 3-3

History Size with Hardware Compression

Hardware compression daughterboards and net modules 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 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 it may not cross

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

contexts, they are signiﬁcant.

Thirty-one CPC contexts each using an 8 KB history are possible on the 32

context board, and 127 contexts each using an 8 KB history are possible on the

128 context board. Table 3-1 indicates the maximum number of 8 KB contexts

each board can support.

On a 32 context board, the maximum number of 32 KB contexts is 7, and on a 128

context board, the maximum number of 32 KB contexts is 31, because of the 8 KB

of memory the one PPC context requires. Table 3-2 summarizes this information.

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.

Table 3-1. Hardware Compression -- 8 KB Contexts

Max 8 KB CPC

Contexts

Available 32 KB

CPC Contexts

Reserved 8 KB

PPC Context

32 Context Board 31 0 1

128 Context Board 127 0 1

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 53 54

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Avaya Configuring Data Compression Services Bedienungsanleitung Seite 41