Cisco WS-C2950SX-48-SI Configuration Manual page 433

Chapter 28 Power Management
Table 28-4 Power Requirements for Some Powered Devices
Device
Cisco legacy IP phone
Cisco + IEEE IP phone
Cisco high-power powered device
Cisco Aironet 1200 Access Point with 802.11a
and 802.11b radio installed
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, Static, 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. If a power outage
occurs, and the mode is set to Static, the phone loses power, but the switching module discovers the
phone and applies the preallocated inline power to the phone.
Powering Off the Phone
The supervisor engine can turn off power to a specific port by sending a message to the switching
module. The power for a port in Auto mode is then added back to the available system power. Power for
ports in Static mode is not added back to the available system power. This situation occurs only when
you power off the phone through the CLI or SNMP.
Phone Removal
The switching module informs the supervisor engine if a powered phone is removed using a link-down
message. The supervisor engine then adds the allocated power for that port back to the available inline
power if the port is in Auto mode.
In addition, the switching module informs the supervisor engine if an unpowered phone is removed.
When you plug a Cisco IP phone into a port and turn the power on, the supervisor engine waits 4 seconds
Caution
for the link to go up on the line. During this time, if you unplug the phone cable and plug in a network
device, you could damage the device. We recommend that you wait at least 10 seconds between
unplugging a device and plugging in a new device.
78-15486-01
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
Understanding How Inline Power Works
Required Power (W)
6.3
7
15.4
11
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Release 8.1
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