Data Compression - 3Com Courier Reference

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HAPTER ANDSHAKING

Data Compression

V.42 bis versus MNP5
Data Compression
, ,
ERROR CONTROL DATA COMPRESSION
Courier V.Everything modems employ different data compression
techniques during data connections.
For the modem to
Disable data compression
Auto-enable/disable data compression. The Courier
V.Everything mode enables compression if the serial
port rate is fixed (&B1) and disables compression if the
serial port rate follows the connection rate (&B0).
Always enable data compression
Selective data compression. Use this setting to transfer
compressed files. The Courier V.Everything modem
negotiates only for V.42 bis compression, and disables
MNP Level 5 (MNP5) compression.
Example: Sending
AT&K3
modem will only negotiate for V.4 bis compression. This command also
will disable MNP Level 5 (MNP5) compression.
If a Courier V.Everything modem successfully establishes a V.42 error
control connection with a remote device, it also negotiates for V.42bis
data compression.
If a Courier V.Everything modem successfully establishes an MNP
connection with a remote device, it also negotiates for MNP5 data
compression.
The type of compression for a call, if any, is reported in the ATI6 display
and in the CONNECT message if the modem is set to &A3
Courier V.Everything modems using V.4 bis compression negotiate the
following options and report them in the ATI6 display
Dictionary size, that is, the amount of memory available for
compression table entries. (Entries are codes devised for redundant
data. The data is packed into shorter data units, called code words,
and unpacked by the receiving device.)
,
AND THROUGHPUT
is used to transfer compressed files. The
Command
AT&K0
AT&K1 (Default)
AT&K2
AT&K3