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Troubleshooting
C-33810-A2-GB30-20 November 1996
Table C-3
(2 of 2)
Modem – VF Connection
Symptom Action
Originate
Mode
Verify that the modem’s DTE Dialer configuration option is set to the correct setting: either AT,
DTR Dialing, V.25bis Async, V.25bis Bisync, or V.25bis HDLC.
Modem does not go
off-hook and begin
dialing
If using AT Dialing, refer to the Table C-2, Modem – DTE Connection.
If using DTR Dialing, verify the telephone number stored in directory location 1, and verify that
the DTE is raising DTR from Off to ON to initiate a dial.
If using V.25bis Async, verify 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 Bisync, verify 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 the text block.
If using V.25bis HDLC, verify 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, verify if a 9 and comma are needed before the
telephone number
.
Verify whether Tone or Pulse dialing is needed.
Verify if one modem is configured for Error Control or Disconnect and the other modem is
configured for no Error Control. Try calling in Buffer mode.
If both modems use V.32bis or V
.32 modulation, set the modem’
s V.32bis Train configuration
option to Long.
Intermittent disconnects,
high error rates, or
excessive
retransmissions
Perform an End-to-End test. Refer to
the
Pattern
section of Chapter 8,
Test Branch
.
Modem establishes and
disconnects a call
You may have a poor VF connection. Disconnect and dial again.
The remote modem may have encountered an EC Disconnect, where the modem is
configured to establish a call using error correction. If the modems cannot negotiate EC, then
a disconnect occurs.
The remote modem may be in a forced Error Control mode (disconnect if there is no error
control). Reconfigure your modem to V.42/MNP or Buffer and try again.
Check the LCD to verify the reason for disconnect.
Perform a Local Analog Loopback test.
High error rates occur
when running a local
loopback or self-test
Incoming rings can cause data errors during a loopback test. Abort the test, disconnect the
modular VF cord, and restart the test.