Toshiba V.90 - Manual (Page 76)

MNP and V.42
Data compression
57
If data transmission from the modem under serial port flow control
is interrupted because the computer cannot catch up with it,
modem port flow control is applied to the remote modem so that
transmitted data will not exceed buffer capacity. This flow control
functions in normal mode only.
Data compression
Protocols MNP class 5 and V.42bis are included in the modem to
compress data received from the computer. The receiving modem
decompresses the received data and sends it to its own computer.
This data compression function increases actual transmission
speed up to twofold in communications using MNP5 or up to
three or fourfold in communications using V.42bis. The
compression ratio varies depending on the data. Actual speed will
not always be raised close to the maximum compression ratio.
Commands (%Cn)
Select whether or not to compress data in communications by
MNP class 5 or V.42bis as follows:
%C1 Enables data compression
For details, refer to “AT Commands” on page 13 .