29-3
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide
—
Release 8.2GLX
78-15908-01
Chapter 29 Configuring VoIP
Configuring VoIP on a Switch
Introducing IP-based phones into 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 on the VLAN that supports the 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 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 requires a new subnet and a new set of IP addresses).
Configuring VoIP on a Switch
To make an IP phone work in your voice network, you must do the following:
•
Configure the auxiliary VLANs for the port.
For more information on setting the auxiliary VLANs, see the
“Configuring Auxiliary VLANs”
section on page 10-13
.
•
Configure inline power if necessary.
The Catalyst 4500 series switch can sense if it is connected to a Cisco IP Phone. The Catalyst 4006
or Catalyst 4500 series switch can supply inline power to a Cisco IP Phone if there is no power on
the circuit. You can connect a Cisco IP Phone to an AC power source, in which case, the phone
provides the power to the voice circuit. If there is power on the circuit, the switch does not supply it.
You can configure the switch to stop supplying power to a Cisco IP Phone and to disable the
detection mechanism. See the
“Configuring PoE” section on page 28-18
for the CLI commands that
you can use to supply inline power to a Cisco IP Phone.