2-4
Cisco Unified IP Phone 7975G Administration Guide for Cisco Unified Communications Manager 7.0 (SCCP and SIP)
OL-15790-01
Chapter 2 Preparing to Install the Cisco Unified IP Phone on Your Network
Providing Power to the Phone
Power Guidelines
Table 2-1
provides guidelines that apply to external power and to PoE power for the Cisco Unified IP
Phone 7975G.
Phone Power Consumption and Display Brightness
The power consumed by a phone depends on its power configuration. See
Table 2-1
for a power
configuration overview. See
Table 2-2
for the maximum power consumed by a phone for each
configuration option and the correlating phone screen brightness level.
Note
Power consumption values shown in the table include power losses in the cable that connects the phone
to the switch.
Table 2-1
Guidelines for Powering the Cisco Unified IP Phone 7975G
Power Type
Guidelines
External power— Provided
through the CP-PWR-CUBE-3
external power supply
The Cisco Unified IP Phone Series use the CP-PWR-CUBE-3 power supply.
External power—
Provided through the Cisco
Unified IP Phone Power Injector
The Cisco Unified IP Phone Power Injector may be used with any Cisco Unified IP Phone.
Functioning as a midspan device, the injector delivers inline power to the attached phone.
The Cisco Unified IP Phone Power Injector is connected between a switch port and the IP
Phone, and supports a maximum cable length of 100m between the unpowered switch and
the IP Phone.
IEEE 802.3af PoE
power—Provided by a switch
through the Ethernet cable
attached to the phone
•
The Cisco Unified IP Phone 7975G support IEEE 802.3af Class 3 power on signal pairs
and spare pairs.
•
The Cisco Unified IP Phone 7975G do not support Cisco inline PoE.
•
To ensure uninterruptible operation of the phone, make sure that the switch has a
backup power supply.
•
Make sure that the CatOS or IOS version running on your switch supports your
intended phone deployment. Refer to the documentation for your switch for operating
system version information.
Table 2-2
Power Consumption and Display Brightness for Power Configurations
Phone Model
Power Configuration
Max. Power
Consumed
from a Switch
Phone
Screen
Brightness
Cisco Unified
IP Phone
7975G
IEEE 802.3af Class 3 power from a Cisco switch, with
bidirectional power negotiation enabled
12 W
Full
External power
—
Full
