3Com 3C421600A Management Manual page 137

Data Compression Tables
A Data Compression Table describes a table of values assigned for each
character during a call using data compression techniques. The default
values in the table are constantly being changed to ensure the most
efficient throughput possible. Each table uses a dictionary to assign these
values.
Dictionary size is the amount of memory available for data compression
table entries. Entries into the table are codes devised for redundant data.
Then data is packed into these shorter data units, called code words, and
unpacked by the receiving device. Possible dictionary sizes are in Table 30.
Table 30 Dictionary Sizes
Bits Entries
9 512
10 1024
11 2048
The RAS 1500 uses an 11-bit, or 2048-entry dictionary, but can reduce its
size to accommodate a remote modem that uses a 9- or 10-bit dictionary.
As the dictionary fills, the RAS 1500 deletes the oldest unused strings.
Configuring Data Compression
The MNP level 5 Disabled setting allows V.42 compression only (for use
when transferring compressed files). MNP-5 compression is not useful
when transferring files that are already compressed because it tends to
add data to the transmission so that throughput over the link degrades.
Table 31 shows the commands used to configure data compression
methods:
Table 31 Data Compression Commands
Action
Disable compression
Auto Enable compression
Enable compression
MNP Level 5 Disabled
Configuring Data Compression Settings
Command
AT&K0
AT&K1 (Default)
AT&K2
AT&K3
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