3Com 56K Lower-speed, Protocols, 32, V.22bis, etc bps and lower, Error Control, Error-Control

	Error Control 12-5
Lower-speed V.	Older, lower-speed "V." protocols do not employ line probing. Instead
Protocols	they use predefined answer tones to specify or identify speed capabilities.
	These protocols define the following maximum speeds:
	■ V.32terbo: 19.2 Kbps, with an additional USR device-to-USR device
	speed of 21.6 Kbps.
	■ V.32bis: 14.4 Kbps.
	■ V.32, V.22bis, etc.: 9600 bps and lower.
	ASL (used in V.32terbo and V.32bis modes) is a technique that allows the
	Business Modem’s receivers and transmitters to act independently of each
	other. One transceiver may slow down and then speed up without
	affecting the data flow on the other. The result is more efficient line
	operation.
	While most modems on the market now use higher speeds, there may be
	a problem in answering older, V.32 modems at 9600 bps. Use Register
	S28 to modify the duration of the extra tones used in V.32 negotiations,
	in the rare instance that this may be necessary. See Appendix A,
	S-Registers.
Error Control	Business Modems can employ error-control techniques during data
	connections.
	High-speed data calls are vulnerable to errors unless the data is protected
	by error control. If your Business Modem connects with a remote device
	at a high speed, but without error control, and if you are not using an
	error control protocol for your call, you may lose data.
	Automatic Repeat Request (ARQ) is a method used in many error-control
	protocols to ensure that any data that has been corrupted in transit is
	retransmitted. We use the term to designate a connection under error
	control.
Error-Control	You can use Error-Control commands to enable ARQ (error control). The
Commands	Business Modem and the remote device must use the same protocol.