3Com Courier, Reference

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Getting Maximum Throughput 13-9
Possible dictionary sizes:
Your modem uses a 12-bit, or 4096-entry dictionary, but can reduce
its size to accommodate a remote modem that uses a 9-, 10-, or
11-bit dictionary.
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Maximum string length of each entry. As the dictionary fills, your
modem deletes the oldest unused strings
V.42 bis compression is more efficient than MNP5 compression, in part
because it dynamically deletes entries that are no longer used. In
addition, it works better with files that are already compressed. These
include .ZIP files and 8-bit binary files.
MNP5 compression should NOT be used with binary files because it adds
data to the files, which lessens throughput. (The additional data is
stripped when the file is decompressed by the remote modem.) When
transferring such files, it's best to set the modem to &K3 (See the
information in data compression). This allows V.42
bis compression to
work dynamically with the compressed data, but disables MNP5.
Getting Maximum
Throughput
The following guidelines should help you to make the most of the
Courier V.Everything modem's advanced performance features. In many
instances, experimentation and experience will indicate what works best
for your applications
Maximum
throughput results
when:
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The communications software allows fixing the serial port rate higher
than the connection rate, by setting the software to 115200, 57600,
or 38400 bps and setting the Courier to &B1.
If the software automatically switches serial port rates to follow the
connection rate, the Courier V.Everything modem's serial port rate
must be also set to follow the connection rate for each call, &B0, an
throughput will be limited.
Bits Entries
9 512
10 1024
11 2048
12 4096