Cisco 7911G - IP Phone VoIP Administration Manual page 238

General Troubleshooting Tips
Table 9-2
Summary
LCD display issues.
Dual-Tone Multi-Frequency
(DTMF) delay.
Loopback condition.
Cisco Unified IP Phone 7906G and 7911G for Cisco Unified Communications Manager 6.0
9-18
Cisco Unified IP Phone Troubleshooting (continued)
Chapter 9 Troubleshooting and Maintenance
Explanation
If the display appears to have rolling lines
or a wavy pattern, it might be interacting
with certain types of older fluorescent
lights in the building. Moving the phone
away from the lights, or replacing the
lights, should resolve the problem.
When you are on a call that requires
keypad input, if you press the keys too
quickly, some of them might not be
recognized.
A loopback condition can occur when the
following conditions are met:
The SW Port Configuration option in
•
the Network Configuration menu on
the phone is set to 10 Half
(10-BaseT / half duplex)
The phone receives power from an
•
external power supply.
The phone is powered down (the
•
power supply is disconnected).
In this case, the switch port on the phone
can become disabled and the following
message will appear in the switch console
log:
HALF_DUX_COLLISION_EXCEED_T
HRESHOLD
To resolve this problem, re-enable the
port from the switch.
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