User`s manual

U.S. Robotics I-modem Command Reference
Handshaking, Error Control, Data Compression, and Throughput • Page 11-15
Analog
If an I-modem successfully establishes a V.42 error control connection with a remote
device, it also negotiates for V.42bis data compression.
If the I-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 (see Chapter 13,
Querying), and in the CONNECT message if the I-modem is set to &A3 (see Chapter 5,
Controlling Result Code Displays).
V.42bis versus MNP5 Data Compression
I-modems using V.42bis 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.)