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Configuring and Managing External Modems
Modem Troubleshooting Tips
DC-154
Cisco IOS Dial Technologies Configuration Guide
Modem Troubleshooting Tips
Table 14 contains troubleshooting tips on modem access and control.
Table 14 Modem Troubleshooting Tips
Problem Likely Cause
Connection refused. Someone already has a connection to that port.
or
an EXEC is running on that port.
or
The modem failed to lower the carrier detect (CD) signal after a call
disconnected, resulting in an EXEC that remained active after disconnect.
To force the line back into an idle state, clear the line from the console
and try again. If it still fails, ensure that you have set modem inout
command for that line. If you don't have modem control, either turn off
EXEC on the line (by using the exec-timeout line configuration
command) before making a reverse connection or configure the modem
using an external terminal. As a last resort, disconnect the modem, clear
the line, make the Telnet connection, and then attach the modem. The
prevents a misconfigured modem from denying you line access.
Connection appears to hang. Try entering “^U” (clear line), “^Q” (XON), and press Return a few times
to try to establish terminal control.
EXEC does not come up; autoselect is on. Press Return to enter EXEC.
Modem does not hang up after entering quit. The modem is not receiving DTR information, or you have not set up
modem control on the router.
Interrupts another user session when you dial in. The modem is not dropping CD on disconnect, or you have not set up
modem control on the router.
Connection hangs after entering “+++” on the
dialing modem, followed by an ATO.
The answering modem saw and interpreted the “+++” when it was echoed
to you. This is a bug in the answering modem, common to many modems.
There may be a switch to work around this problem; check the modem’s
documentation.
Losing data. You may have Hardware Flow Control only on for either the router’s line
(DTE) or the modem (DCE). Hardware Flow Control should be on for
both or off for both, but not for only one.
Using MDCE. Turn MDCE into an MMOD by moving pin 6 to pin 8 because most
modems use CD and not DSR to indicate the presence of carrier. You can
also program some modems to provide carrier info via DSR.