Explanation
Summary
A loopback condition can occur when the following
conditions are met:
• The SW Port Configuration option 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 appears in the
switch console log:
HALF_DUX_COLLISION_EXCEED_THRESHOLD
To resolve this problem, reenable the port from the
switch.
Loopback condition
Startup Problems
After you install a phone into your network and you can access the phone web page (phone Configuration
Utility), the phone should start up as described in the related topic below.
If the phone does not start up properly, see the following sections for troubleshooting information.
Cisco IP Phone Does Not Go Through the Normal Startup Process
Problem
When you connect a Cisco IP Phone to the network port, the phone does not go through the normal startup
process as described in the related topic and the phone screen does not display information.
Cause
If the phone does not go through the startup process, the cause may be faulty cables, bad connections, network
outages, lack of power, or the phone may not be functional.
Solution
To determine whether the phone is functional, use the following suggestions to eliminate other potential
problems.
• Verify that the network port is functional:
• Exchange the Ethernet cables with cables that you know are functional.
• Disconnect a functioning Cisco IP Phone from another port and connect it to this network port to
verify that the port is active.
Cisco IP Phone 7800 Series Multiplatform Phones Administration Guide
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Cisco IP Phone Troubleshooting
Startup Problems
