Paradyne 3760 User Manual

Also see for KeepInTouch 3760: User guide

Paradyne 3760 User Manual Manual pdf 75 page image

Advanced Modem ConceptsD-4 Issue 1 November 1994Modem-to-Computer Flow ControlOften, your computer is able to send data to your modem fasterthan the modem can transmit it across the telephone line. As aresult, the modem’s buffer begins to fill with data received fromthe computer. To prevent the buffer from filling and overflowing,which would result in data loss and errors, the modem tells thecomputer to stop sending data.When the modem’s buffer is almost full (usually 80%), it tells thecomputer to stop sending data as illustrated in Figure D-1. Oncethe modem has a chance to transmit its buffered data, it tells thecomputer to continue sending data.Figure D-1. Modem-to-Computer Flow ControlTo do this, the modem can use either software characters(XON/XOFF) embedded in the data stream or hardwaresignals (CTS/RTS) on the serial connector to control data flow.The \Q command lets you determine which flow control methodthe modem uses to stop data from the computer, as well aswhich method the computer uses to stop data from the modem.In some situations, the computer can stop data flow from themodem as illustrated in link A—B of computer-to-modem flowcontrol in Figure D-2. In this instance, if Computer A’s bufferbegins to fill, it can stop data flow by sending an XOFF toModem B or by lowering its RTS signal to Modem B.