3Com REMOTE ACCESS SYSTEM 1500, Management Manual

Page: 139 / 300

Configuring Error Control Options
137
Microcom Networking Protocol Error Control
Microcom Networking Protocol (MNP) is supported by the ITU-T V.42
Recommendation. It was originally developed by Microcom®, Inc. and is
now in the public domain. MNP is based on special protocol frames. If the
remote device does not recognize an MNP Link Request, error control is
not possible.
Error and Flow Control
Flow control of data from the computer is required under error control for
two reasons:
■
The transmitting device buffers a copy of each frame it transmits to
the remote end until it is acknowledged by the receiving device.
■
If errors are encountered, retransmission activity can cause a steady
stream of data from the computer to overflow the buffer.
Error control is required for data compression and recommended for all
calls above 2400 bps.
Cyclic redundancy checking is used to detect errors. An ARQ is issued
when a corrupted data frame is detected, and the data frame is
retransmitted. ARQ denotes error control in U.S. Robotics error control
commands and response codes.
A modem can retransmit a data frame a maximum of twelve times, after
which the modem aborts the call. Disconnection from retry timeout only
occurs under serious line disturbances.
Using Error Control Disabling Error Control
Action Command Default
Disable error control. Not recommended for
calls above 2400 bps. AT&M0 AT&M4 (Enabled)