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Cisco Unified IP Phone 7970G/7971G-GE Administration Guide for Cisco Unified Communications Manager 7.0
OL-15299-01
Chapter 2 Preparing to Install the Cisco Unified IP Phone on Your Network
Providing Power to the Phone
Understanding How the Cisco Unified IP Phone Interacts with the VLAN
The Cisco Unified IP Phone 7970 Series have an internal Ethernet switch, enabling forwarding of
packets to the phone, and to the access port and the network port on the back of the phone.
If a computer is connected to the access port, the computer and the phone share the same physical link
to the switch and share the same port on the switch. This shared physical link has the following
implications for the VLAN configuration on the network:
• The current VLANs might be configured on an IP subnet basis. However, additional IP address
might not be available to assign the phone to the same subnet as other devices connect to the same
port.
• Data traffic present on the data/native VLAN may reduce the quality of Voice-over-IP traffic.
• Network security may indicate a need to isolate the VLAN voice traffic from the VLAN data traffic.
You can resolve these issues by isolating the voice traffic onto a separate VLAN. The switch port that
the phone is connected to would be configured to have separate VLANs for carrying:
• Voice traffic to and from the IP phone (auxiliary VLAN, on the Cisco Catalyst 6000 series, for
example)
• Data traffic to and from the PC connected to the switch through the access port of the IP phone
(native VLAN)
Isolating the phones on a separate, auxiliary VLAN improves the quality of the voice traffic and allows
a large number of phones to be added to an existing network where there are not enough IP addresses
for each phone.
For more information, refer to the documentation included with a Cisco switch. You can also access
related documentation at this URL:
http://cisco.com/en/US/products/hw/switches/index.html
Related Topics
• Understanding the Phone Startup Process, page 2-7
• Network Configuration Menu, page 4-5
Providing Power to the Phone
Models in the Cisco Unified IP Phone 7970 Series can be powered with external power or with Power
over Ethernet (PoE). External power is provided through a separate power supply. PoE is provided by a
switch through the Ethernet cable attached to a phone.
Note When you install a phone that is powered with external power, connect the power supply to the phone
and to a power outlet before you connect the Ethernet cable to the phone. When you remove a phone that
is powered with external power, disconnect the Ethernet cable from the phone before you disconnect the
power supply.
The following sections provide more information about powering a phone:
• Power Guidelines, page 2-4
• Phone Power Consumption and Display Brightness, page 2-5