55-9
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 55 Configuring a VoIP Network
Understanding How VLANs Work
Note
For more information about the VLANs, see
Chapter 11, “Configuring VLANs.”
Figure 55-3
shows how to connect a Cisco IP Phone 7960 to a Catalyst 6500 series switch.
Figure 55-3
Switch-to-Phone Connections
When the IP phone connects to a 10/100 port on the Catalyst 6500 series switch, the
access port
(PC-to-phone jack) of the IP phone can be used to connect a PC.
The packets to and from the PC and to and from the phone share the same physical link to the switch and
the same port of the switch. The various configurations are shown in the
“Cisco IP Phone 7960” section
on page 55-2
).
Introducing the IP-based phones into the existing switch-based networks raises the following issues:
•
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) that are connected to the same port.
•
The data traffic present on the VLAN supporting phones might reduce the quality of the VoIP traffic.
You can resolve these issues by isolating the voice traffic onto a separate VLAN on each of the ports that
are connected to a phone. The switch port that is configured for connecting a phone would have separate
VLANs that are configured for carrying the following:
•
Voice traffic to and from the IP phone (auxiliary VLAN)
•
Data traffic to and from the PC that is 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.
A new VLAN means a new subnet and a new set of IP addresses.
3-port
switch
P1
P3
P2
Access
port
Cisco IP Phone 7960
Workstation/PC
Catalyst switch
10/100 module
38204
Phone
ASIC
