3Com AccessBuilder 980/000048/001, User Manual

Page: 34 / 60

3 - 4 C
H A P T E R
3: T
R O U B L E S H O O T I N G
Connection Problems When Originating a Call
Modem fails to go off-hook and originate a call
Check t hat 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 t he telephone number stored in directory
location 1, and check t hat the DTE is raising DTR from OFF to ON to
initiate a dial.
If using V.25bis asynchronous dialling, check t hat 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 t hat 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 t hat 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 i f a 9 and comma are
needed before the telephone number.
Check w hether tone or pulse dialling is needed.
Check i f 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.