User`s manual

U.S. Robotics I-modem Command Reference
Handshaking, Error Control, Data Compression, and Throughput • Page 11-13
Error-Control Commands
&Mn Enable ARQ (error control) or enable synchronous
protocols. The I-modem and
the remote device must use the same protocol
.
&M0 Normal mode, no error control. Due to the nature of phone line channels,
this is never recommended for analog calls above 2400 bps.
&M1 Online synchronous mode without V.25bis. External I-modems only.
&M4 Normal/ARQ mode. Operate in Normal mode (&M0) if an ARQ connec-
tion canÕt be made.
Note When V.32-type devices revert to Normal mode (&M0), they transfer data
at high speeds without the reliability of error control. To avoid this, both
local and remote devices should always be set for error control. USR
devices in HST mode drop to 2400 bps if theyÕre unable to establish an
error-control connection.
&M5 Enter ARQ asynchronous
mode. The I-modem hangs up if it canÕt make an
ARQ connection.