V.42bis/MNP2-4 Error Control &Q9
In V.42bis/MNP2-4 Error Control the modem attempts to negotiate a V.42bis
error-control link upon connection. If V.42bis (or V.42) is not achieved,
then MNP2-4 is attempted. If neither error-control protocol is established,
the modem falls-back according to the current setting in S36. If S36 bit
0 is 0 the modem hangs-up. If S36 bit 0 is 1 the modem connects according
to S36 bit 1. If S36 bit 1 is 0 the modem connects in Direct Async mode.
If S36 bit 1 is 1 the modem connects in Buffered Async mode.
The settings in S48 and S46 are ignored. If fall-back to Buffered Async
mode occurs, all data received during protocol negotiations is present in
the received data buffer. &Kn determines the type of local flow-control
while in error-control or buffered modes.
The diagram in the Error-control Mode - &Q5
section depicts modem operation in this mode.