Error Control 12-5Lower-speed V.ProtocolsOlder, lower-speed "V." protocols do not employ line probing. Insteadthey use predefined answer tones to specify or identify speed capabilities.These protocols define the following maximum speeds:n V.32terbo: 19.2 Kbps, with an additional USR device-to-USR devicespeed of 21.6 Kbps.n V.32bis: 14.4 Kbps.n V.32, V.22bis, etc.: 9600 bps and lower.ASL (used in V.32terbo and V.32bis modes) is a technique that allows theBusiness Modem’s receivers and transmitters to act independently of eachother. One transceiver may slow down and then speed up withoutaffecting the data flow on the other. The result is more efficient lineoperation.While most modems on the market now use higher speeds, there may bea problem in answering older, V.32 modems at 9600 bps. Use RegisterS28 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 dataconnections.High-speed data calls are vulnerable to errors unless the data is protectedby error control. If your Business Modem connects with a remote deviceat a high speed, but without error control, and if you are not using anerror control protocol for your call, you may lose data.Automatic Repeat Request (ARQ) is a method used in many error-controlprotocols to ensure that any data that has been corrupted in transit isretransmitted. We use the term to designate a connection under errorcontrol.Error-ControlCommandsYou can use Error-Control commands to enable ARQ (error control). TheBusiness Modem and the remote device must use the same protocol.
