Cisco Systems 7940G Manual De Usuario

 provides general troubleshooting information for the Cisco Unified IP Phone.

Connecting a Cisco Unified IP Phone 
to another Cisco Unified IP Phone/

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.

Poor quality when calling digital 
mobile phones using the G.729 
protocol.

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 mobile 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 Communications Manager server.

Moving a network connection from 
the phone to a workstation.

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 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.

Changing the telephone 
configuration.

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 the 

 for details.

Phone resetting.

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.

LCD display issues.

If the display appears to have rolling lines or a wavy pattern, it might be interacting 
with certain types of older fluorescent lights in the building. Moving the phone away 
from the lights, or replacing the lights, should resolve the problem.

Dual-Tone Multi-Frequency (DTMF) 
delay.

When you are on a call that requires keypad input, if you press the keys too quickly, 
some of them might not be recognized.

Codec mismatch between the phone 
and another device.

The RxType and the TxType statistics show the codec that is being used for a 
conversation between this IP phone and the other device. The values of these statistics 
should match. If they do not, verify that the other device can handle the codec 
conversation or that a transcoder is in place to handle the service. 

See the 

 for information about displaying 

these statistics.