Cisco 7912G - Manual (Page 52)

Chapter 2 Preparing to Install the Cisco Unified IP Phone on Your Network
Providing Power to the Cisco Unified IP Phone
2-10
Cisco Unified IP Phone Administration Guide for Cisco Unified CallManager 5.0 (SIP), Cisco Unified IP Phones
OL-8131-01
• Power Source Design, page 2-10
• Redundancy Feature, page 2-11
• Installing the Cisco Unified IP Phone, page 3-6
Power Outage
Your accessibility to emergency service through the phone is dependent on the
phone being powered. If there is an interruption in the power supply, Service and
Emergency Calling Service dialing will not function until power is restored. In the
case of a power failure or disruption, you may need to reset or reconfigure
equipment before using the Service or Emergency Calling Service dialing.
Power Source Design
The phone and switch automatically determine which power source the phone
uses. If the power has to be switched to a different source, the phone user will
experience different results based on which power source is being used by the
phone.
Use the following information to choose a power source for the phone:
• If you plug a phone into the optional power supply before plugging it into the
network, the phone is powered by the power supply.
• If you then unplug the phone from the power supply, the phone resets. If the
switch port is configured for 10/100 Mbps, the switch recognizes the loss of
power and brings the phone back up.
• If the switch port is configured for 10 Mbps only, then you must unplug the
network connection and plug it back into the phone for the switch to
recognize the phone’s loss of power.
• If, however, you plugged the network connection into the phone before you
plugged in the power cord, the phone receives power through the switch, and
unplugging the power cord will not bring down the phone. If the switch
reboots, the phone will then be powered by the power cord.