Cisco 7941G Troubleshooting And Maintenance page 17

Troubleshooting and Maintenance
Table 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
Changing the telephone configuration
Phone resetting
General Troubleshooting Information
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 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 protocol 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.
The network card in the computer cannot
Caution
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.
By default, the network configuration options are
locked to prevent users from making changes that
could impact their network connectivity. You must
unlock the network configuration options before you
can configure them. See Unlock and Lock Options
for details.
The phone resets when it loses contact with the Cisco
Unified Communications Manager software. This lost
connection can be due to any network connectivity
disruption, including cable breaks, switch outages,
and switch reboots.
Troubleshooting and Maintenance
17