
Data Compression Parameters
117352-B Rev. 00
A-3
Parameter: History Size
Path: Configuration Manager > Protocols > WCP > Lines
Default: 32 K
Options: 32 K
|
8 K
Function: Indicates 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 software compression with a 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 32 K for PPP WCP should not be a problem for the BN, because PPP
allows only one circuit per single or multiple lines. Select 8 K or 32 K for frame
relay and X.25 lines, depending on the resources of your network.
Selecting 32 K 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 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 than an 8 KB history.
If you select different history sizes for each side 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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