Cisco MGCP IP Phone Administrator's Manual page 27

Chapter 2 Installing the Cisco MGCP IP Phone
If a computer is connected to the access port, packets traveling to and from the computer and to and from
the phone share the same physical link to the switch and the same port on the switch.
This configuration has these implications for the VLAN configuration on the network:
• The current VLANs might be configured on an IP subnet basis, and additional IP addresses might
not be available to assign the phone to a port so that it belongs to the same subnet as other devices
(PC) connected to the same port.
Data traffic present on the VLAN supporting phones might reduce the quality of VoIP 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 Cisco MGCP IP phone (auxiliary VLAN)
•
• Data traffic to and from the PC connected to the switch through the access port of the Cisco MGCP
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 or available
online at the following URL:
http://www.cisco.com/univercd/home/index.htm
Using the Cisco MGCP IP Phone with a Catalyst Switch
Cisco MGCP IP Phone Administrator Guide, Release 5.0 and Release 5.1
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