Toshiba V.90 - Manual (Page 72)

MNP and V.42
Operation modes
53
The protocol of both modems must be the same. Therefore, if the
remote modem supports only class 3 or below, the protocol for the
remote modem will be used. If the remote modem does not use
MNP, the communication will be made at the speed of the remote
modem.
V.42 error correction
The V.42 (ITU-T-Rec V.42) protocol is recommended by the ITU
(International Telecommunications Union). V.42 specifies two
kinds of protocols, LAP-M (Link Access Procedure for Modem)
and MNP classes 2, 3, and 4. This protocol first tries to establish a
link to the remote modem with LAP-M. If it is unsuccessful, it
tries to connect with MNP. Although this modem uses class 4
correction, it can connect in class 5 to remote modems that support
class 5.
Operation modes
The operation mode depends on whether an error-correction
protocol is being used.
Normal mode
Errors are not corrected, even if communication speed is different
between a personal computer and modem, or between modems,
the buffers in the modem and the flow control function permit
communication without changing communication speed.
Reliable mode
This mode is used with MNP or V.42 protocols to ensure error-
free communication.