Cisco WS-X6066-SLB-APC - Content Switching Module Software Manual page 829

Chapter 44 Configuring a VoIP Network
These sections provide information related to IP phone power requirements and management:
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Unpowered Phone
When an unpowered phone is discovered on a switching module port, the switching module reports to
the supervisor engine that an unpowered phone is present and on which module/port. If the port is
configured in Auto mode, the supervisor engine determines if there is enough available system power
to allow the switching module to power up and run the phone. If there is sufficient power, the supervisor
engine removes the default allocated power required by a phone from the total available system power
and then sends a message to the switching module instructing it to provide power to the port. If there is
not enough available power for the phone, the supervisor engine sends a message to the switching
module indicating that power is denied to the port.
After power is applied to the port, the supervisor engine monitors the port to ensure that the link comes
up. If the link does not come up within 4 seconds, the supervisor engine instructs the switching module
to turn power off. The entire cycle is repeated, and the switching module performs discovery and reports
to the supervisor engine if a device is present on the port.
Power Requirements
IP Phones may have different power requirements. The supervisor engine initially allocates the
configured default of 7W (167 mA at 42V) to the Cisco IP Phone. When the correct amount of power is
determined from the CDP messaging with the Cisco IP Phone, the supervisor engine reduces or increases
the allocated power.
For example, the default allocated power is 7W. A Cisco IP Phone requiring 6.3W is plugged into a port.
The supervisor engine allocates 7W for the Cisco IP Phone and powers it up. Once the Cisco IP Phone
is operational, it sends a CDP message with the actual power requirement to the supervisor engine. The
supervisor engine then decreases the allocated power to the required amount.
Wall-Powered Phones
When a wall-powered phone is present on a switching module port, the switching module cannot detect
its presence. The supervisor engine discovers the phone through CDP messaging with the port. If the
phone supports inline power (the supervisor engine determines this through CDP), and the mode is set
to Auto or Off, the supervisor engine does not attempt to power on the port. If a power outage occurs,
and the mode is set to Auto, the phone loses power, but the switching module discovers the phone and
informs the supervisor engine, which then applies inline power to the phone.
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Unpowered Phone, page 44-13
Power Requirements, page 44-13
Wall-Powered Phones, page 44-13
Powering Off the Phone, page 44-14
Phone Removal, page 44-14
High-Availability Support, page 44-14
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
Configuring VoIP on a Switch
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