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Troubleshooting
C-33821-A2-GB20-30 February 1998
Table C-5
(1 of 2)
Modem – VF Connection
Symptom
Action
Modem does not receive a
dial tone
Check the VF line connection. Verify dial tone at the source.
Modem does not go
off-hook and answer an
incoming call
Verify that the Auto-Answer Ring Count configuration option (S-register 0) is set to a value
other than 0 (disable).
incoming call
Verify that the DTE is providing DTR to the modem.
If the DTE does not provide DTR to the modem, verify that the modem’s &D command
(DTR Action configuration option) is set for Ignore (&D0).
Verify all cabling.
Modem goes off-hook,
answers, but does not
connect
Perform a Local Analog Loopback test and verify that data entered at the DTE is echoed
back to the DTE.
connect
Verify that the originating modem is compatible.
Verify that originating modem recognizes your modem’s answer tone.
Modem goes off-hook,
answers, but does not
connect (continued)
Verify that originating modem supports your modem’s modulation schemes. The 3821
Plus
modem recognizes V.34, V.32
terbo,
V.32bis, V.32, V.22bis, V.22, V.21, Bell 212A, and
Bell 103J. It does not support other vendors’ proprietary modulation schemes.
Use the S41 register to force your modem to operate at the same modulation scheme as
the originating modem.
Originate Mode Verify that the modem’s DTE Dialer configuration option is set to the correct setting.
Modem does not go
off-hook and begin dialing
If using AT Dialing, refer to the Table C-4, Modem – DTE Connection.
off-hook and begin dialing
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, determine if a 9 and comma are needed before
the telephone number.
Determine 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.34, V.32bis, or V.32 modulation, set the modem’s Train Time
configuration option to Long.