3Com 980/000048/001 manual Troubleshooting

3-4 CHAPTER 3: TROUBLESHOOTING

Connection Problems When Originating a Call

Modem fails to go off-hook and originate a call

Check that the modem’s configuration enables either AT dialling or V.25bis dialling. Note: A modem configured to accept AT commands cannot accept V.25bis commands, and vice versa.

If using DTR dialling, check the telephone number stored in directory location 1, and check that the DTE is raising DTR from OFF to ON to initiate a dial.

If using V.25bis asynchronous dialling, check that the correct character format is set to 7 data bits with even parity and 1 stop bit, and the carriage return and line feed are used as command terminators.

If using V.25bis bisynchronous dialling, check that the correct character format uses two synchronous control characters and a start-of-text control character before the text block, and an end-of-text control character after it.

If using V.25bis HDLC, check that the correct character format uses flag, address and control characters before the text block, and a frame sequence check and flag after the text block.

Modem dials but does not connect

If the modem is operating behind a PBX, check if a 9 and comma are needed before the telephone number.

Check whether tone or pulse dialling is needed.

Check if one modem is configured for error correction or disconnect, and the other modem is configured for no error correction. Try initiating the call in buffer mode.

If both modems use V.32bis or V.32, set the modem’s V.32bis training configuration option to Long.