3Com 56K manual For the modem to Command, AT&K0, AT&K2, AT&K3

12-8CHAPTER 12: HANDSHAKING, ERROR CONTROL, DATA COMPRESSION, AND THROUGHPUT

Data Compression Business Modems employ different data compression techniques during data connections.

For the modem to	Command
Disable data compression	AT&K0
Auto-enable/disable data compression. The Business	AT&K1 (Default)
Modem 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	AT&K2
Selective data compression. Use this setting to transfer	AT&K3
compressed files. The Business Modem negotiates only
for V.42bis compression, and disables MNP Level 5
(MNP5) compression.

Example: Sending AT&K3 is used to transfer compressed files. The modem will only negotiate for V.42bis compression. This command also will disable MNP Level 5 (MNP5) compression.

If a Business Modem successfully establishes a V.42 error control connection with a remote device, it also negotiates for V.42 bis data compression.

If a Business 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.

V.42bis versus MNP5 Business Modems using V.42bis compression negotiate the following Data Compression 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.)