MNP and V.42

97

Flow control

Commands (\Nn)

The following N modulation handshake commands are used to set the communication mode:

\N0, \N1

Remote modem unable to use MNP or V.42

\N2

Remote modem uses MNP

\N3

Uncertain if remote modem can use MNP or

 

V.42

\N4

Remote modem uses V.42

\N5, \N7

Same as \N3

For details, refer to “AT Commands” on page 51.

Flow control

In both normal mode and reliable mode, the buffers in the modem and its flow control function permit communication even if the speed is different between a personal computer and modem (serial port) or between modems (modem port).

If there is a speed difference between the serial port and modem port, the buffers in the modem will become full periodically. Therefore, the communication activity is controlled so that data transmission or reception is temporarily halted before the data exceeds buffer capacity, and transmission is resumed when the receiving buffers have room. This is the flow control function.

The modem card has two kinds of flow control:

❖Serial port flow control

❖Modem port flow control (only in reliable mode)