Cisco 7912G User Manual
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Cisco Unified IP Phone Administration Guide for Cisco Unified CallManager 5.0 (SIP), Cisco Unified IP Phones
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Chapter 7 Troubleshooting the Cisco Unified IP Phone
General Troubleshooting Tips for the Cisco Unified IP Phone
General Troubleshooting Tips for the Cisco Unified
IP Phone
provides general troubleshooting information for the Cisco Unified IP
Phones.
Table 7-1
Cisco Unified IP Phone Troubleshooting
Summary
Explanation
Daisy-chaining IP phones
Do not connect an IP phone to another IP phone through the
access port. Each IP phone should directly connect to a switch
port. If you connect IP phones together in a line
(daisy-chaining), a problem with one phone can affect all
subsequent phones in the line. Also, all phones on the line share
bandwidth.
Poor quality when calling digital cell
phones using the G.729 protocol
In Cisco Unified CallManager, 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.
Prolonged broadcast storms cause IP
phones to re-register
Prolonged broadcast storms (lasting several minutes) on the
voice VLAN cause the IP phones to re-register with another
Cisco Unified CallManager server.
Moving a network connection from
the phone to a workstation
If you are powering a 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.