USRobotics V.34 user manual Other V. Protocol Operations

COURIER HIGH SPEED MODEMS

OTHER V. PROTOCOL OPERATIONS

Earlier, lower-speed V. protocols do not employ line probing. Instead they use predefined answer tones to specify, or identify, speed capabilities. These protocols define the following maximum speeds.

∙V.32 terbo: 19.2K bps, with an additional Courier-to- Courier speed of 21.6K bps.

∙V.32 bis: 14.4K bps.

∙V.32: 9600 bps.

ASL (used in V.32 terbo and V.32 bis modes) is a strategy that allows the modems' receivers and transmitters to act independently of each other. We have always featured a fallback/fall forward feature with error-correcting modems that allows them to slow down if there are problems with the phone line, in order to avoid data errors, and then speed up again. But the independence of the receiving and transmitting channels means that one channel or the other may slow down and then speed up, without affecting the data flow on the other. The result is more efficient line operation.

WARNING: Answering V.32 terbo modems shift their serial port rate up to 38.4K (for 21.6K connections) if the calling V.32 terbo modem dials in at 21.6K. The answering V.32 terbo modem then sends data to its computer at 38.4K bps. V.32 bis modems shift their serial port rate to 19.2K bps in order to make 14.4K bps connections. If your ocomputer or terminal does not support these higher serial port rates, you need to disable V.32 terbo and/or V.32 bis. See Appendix B, Register S34.

NOTE: While many modems on the market now use the more efficient speeds, there may be a problem in answering older, "dumb" V.32 modems at 9600 bps. Register S28 is used to modify the duration of the extra tones used in V.32 negotiations, in the rare instance that this may be necessary. See S-Registers, in Appendix B.

Link Negotiation and Error Control A-3