3Com 56K manual Scheme similar to MNP, Flow Control, Two reasons

Error Control 12-7

V.42 Error Control The Business Modem first tries for a V.42 connection, then an MNP connection. The following information is based on the Business 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 predefined characters.

■A Link Access Procedures for Modems (LAPM) Negotiation phase, during which the devices identify their capabilities concerning maximum data block size and the number of outstanding data blocks allowed before an acknowledgment is required.

MNP Error Control	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.)
Error Control and	Flow control of data from the computer is required under error control for
Flow Control	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.