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V.42 Error Control
MNP Error Control
Error Control and
Flow Control
The Courier V.Everything modem first tries for a V.42 connection, then a
MNP connection. The following information is based on the Courier
V.Everything modem's setting of &M4
This international standard includes a two-stage hand-shaking process:
A Detection phase that is based on an exchange of predefine
characters.
A Link Access Procedures for Modems (LAPM) Negotiation
phase, during which the devices identify their capabilities concernin
maximum data block size and the number of outstanding data blocks
allowed before an acknowledgment is required.
The Microcom Networking Protocol (MNP) is supported by the ITU-T V.42
Recommendation. MNP is based on special protocol frames. If the remote
device doesn't recognize an MNP Link Request, error control isn't
possible. (In HST asymmetrical mode, 3Com devices use a proprietary
scheme similar to MNP.
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 t
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
13-7
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