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Cisco IP Phone Administration Guide for Cisco CallManager 3.3, Cisco IP Phones 7902G/7905G/7912G
OL-6313-01
Chapter 2 Preparing to Install the Cisco IP Phone on Your Network
Understanding Interactions with Other Cisco IP Telephony Products
Understanding How the Cisco IP Phone Interacts with the
Cisco Catalyst Family of Switches
The Cisco IP Phone 7912G has an internal Ethernet switch, enabling it to switch
incoming traffic to the phone, the access port, or to the network port (see the
“Connecting to the Network” section on page 2-8 for details). The Cisco IP Phone
models 7902G/7905G do not include an internal Ethernet switch or an access port.
If a computer is connected to the access port, the computer and the phone share
the same physical link to the switch and 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 addresses may not be available to assign the phone to the same
subnet as other devices connected to the same port.
• Data traffic present on the VLAN supporting phones might reduce the quality
of Voice-over-IP traffic.
You can resolve these issues by isolating the voice traffic onto a separate VLAN
on each of the ports connected to a phone. The switch port configured for
connecting a phone would have separate VLANs configured for carrying:
• Voice traffic to and from the IP phone (auxiliary VLAN)
• 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 increases 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 more information, refer to the documentation included with the
Cisco Catalyst switch.
Related Topics
• Connecting to the Network, page 2-8
• Understanding the Phone Startup Process, page 2-4
• Modifying VLAN Settings, page 4-24