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3-2 CHAPTER 3: TROUBLESHOOTING
The 3Com Impact digital modem will not operate if
connected to an analog telephone wall jack. Make sure that
the digital modem is connected directly into the ISDN wall
outlet without connection to any intermediate telephone
equipment (an NT1 device is not required with this digital
modem).
4 Make sure that the cables provided by 3Com or a 3Com
authorized reseller are in good condition and show no
evidence of wear or other physical damage.
If damage is apparent after close inspection, contact your
reseller for replacement cables.
5 Monitor the status of the D channel LED.
■ If you are connected to a live digital ISDN line, the
D channel LED remains lit for up to a few minutes after
the self-test but then begins to flash.
When the D channel LED flashes, it indicates that the
ISDN signal is present.
When the D channel LED goes out, it indicates that a
valid communication channel has been established and
calls may be attempted by the user.
■ If the D channel LED remains lit after more than a few
minutes, it is likely that there is a poor physical
connection to the local telephone company.
This fault can be caused by a damaged cable, a broken
wire, a damaged connector, a nonstandard U interface
(proprietary AMI line coding), or a problem within the
telephone company network. If the telephone wires at
your site appear to be satisfactory, call your local
telephone company for repair of telephone company
equipment and troubleshooting assistance.
■ If the D channel LED flashes for more than a few minutes
without going out, there is probably a mismatch between
the settings of the ISDN line and the 3Com Impact digital
modem configuration.