Cisco 8831NR Administration Manual page 140

General Troubleshooting Information
Summary
Loopback condition
Moving a network connection from
the conference phone to a
workstation
No dial tone
No LCD screen display
One-way audio
Cisco Unified IP Conference Phone 8831 and 8831NR Administration Guide
130
Explanation
A loopback condition can occur when the following conditions are met:
• The conference phone receives power from an external power
supply
• The conference phone is powered down (the power supply is
disconnected)
In this case, the switch port on the conference phone can become
disabled and the following message will appear in the switch console
log:
HALF_DUX_COLLISION_EXCEED_THRESHOLD
To resolve this problem, re-enable the port from the switch.
If you are powering your conference phone through the network
connection, you must be careful if you decide to unplug the conference
phone network connection and plug the cable into a desktop computer.
The computer's network card cannot receive power through
Caution
the network connection; if power comes through the
connection, the network card can be destroyed. To protect a
network card, wait 10 seconds or longer after unplugging
the cable from the conference phone before plugging it into
a computer. This delay gives the switch enough time to
recognize that there is no longer a conference phone on the
line and to stop providing power to the cable.
Check that all connections are secure and in place. Make sure all
connections are correct.
Check to make sure that the conference phone has power. Make sure
that the power supply unit is plugged in.
When at least one person in a call does not receive audio, IP connectivity
between conference phones is not established. Check the configurations
in routers and switches to ensure that IP connectivity is properly
configures.
Troubleshooting and Maintenance