User`s manual

U.S. Robotics I-modem Command Reference
Handshaking, Error Control, Data Compression, and Throughput • Page 11-10
If you want the I-modem connect with V. protocol modems at high speeds, make sure it is
set to B0 for the ITU answer tones. It will also connect with HST modems at speeds up to
16.8 Kbps.
Error Control
I-modems employ error-control techniques only during V.120 and analog connections.
Note High-speed analog calls are highly vulnerable to errors unless the data is
protected by error control. The operations described below take place even
if the I-modem or remote analog device is not set for error control. If your
I-modem connects with a remote analog device at a high speed, but without
error control, and if you are not using an error control protocol
for your
call, you may lose data.
Some of the following text includes the term ARQ, which stands for Automatic Repeat
Request. ARQ is a method used in many error-control protocols to ensure that any data
that has been corrupted in transit is retransmitted. We use the term to designate a connec-
tion under error control.