Checking Power Connection; General Troubleshooting Tips - Cisco 6921 Administration Manual

General Troubleshooting Tips

From Cisco Unified Communications Manager, choose System > Server and verify that the server is
Step 4
referred to by its IP address and not by its DNS name.
Step 5 From Cisco Unified Communications Manager, choose Device > Phone > Find and verify that you have
assigned the correct MAC address to this Cisco Unified IP Phone. For information about determining a
MAC address, see the
page
Power cycle the phone.
Step 6

Checking Power Connection

In most cases, a phone will restart if it powers up by using external power but loses that connection and
switches to PoE. Similarly, a phone may restart if it powers up by using PoE and then gets connected to
an external power supply.
General Troubleshooting Tips
Table 9-1
Table 9-1 Cisco Unified IP Phone Troubleshooting
Summary
Connecting a Cisco Unified IP Phone to
another Cisco Unified IP Phone/
Poor quality when calling digital cell
phones using the G.729 protocol.
Prolonged broadcast storms cause
IP phones to reset, or be unable to make or
answer a call.
Moving a network connection from the
phone to a workstation.
Cisco Unified IP Phone 6921, 6941, and 6961 Administration Guide for Cisco Unified Communications Manager 7.1 (SCCP)
9-8
"Determining the MAC Address for a Cisco Unified IP Phone" section on
2-10.
provides general troubleshooting information for the Cisco Unified IP Phone.
Explanation
Cisco does not support connecting an IP phone to another IP phone through the
PC port. Each IP phone should directly connect to a switch port. If phones are
connected together in a line (by using the PC port), the phones will not work.
In Cisco Unified Communications Manager, you can configure the network to
use the G.729 protocol (the default is G.711). When using G.729, calls between
an IP phone and a digital cellular phone will have poor voice quality. Use G.729
only when absolutely necessary.
A prolonged Layer 2 broadcast storm (lasting several minutes) on the voice
VLAN may cause IP phones to reset, lose an active call, or be unable to initiate
or answer a call. Phones may not come up until a broadcast storm ends.
If you are powering your phone through the network connection, you must be
careful if you decide to unplug the phone's network connection and plug the
cable into a desktop computer.
Caution
The computer's network card cannot receive power through 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 phone before
plugging it into a computer. This delay gives the switch enough time
to recognize that there is no longer a phone on the line and to stop
providing power to the cable.
Chapter 9 Troubleshooting and Maintenance
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