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Overview of IP Phones
Overview of IP Phones
Catalyst 4000, 4500, 2926G, or 2926 series switches can connect to an IP Phone and carry IP voice
traffic. If necessary, the switch can supply electrical power to the circuit connecting it to an IP Phone.
Cisco classifies three types of IP phones based on the discovery methods that are used to discover the
phone:
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•
•
An IP phone contains an integrated three-port 10/100 switch. The ports are dedicated connections as
described below:
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•
•
Figure 29-1
Figure 29-1 IP Phone Connected to a Catalyst 4000 Family Switch
Catalyst 4000 Family Switch
When you connect an IP phone to a 10/100 port on the Catalyst 4500 series switch, you can use the
access port (PC-to-phone jack) of the IP phone to connect a PC.
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.
Introducing IP-based phones into existing switch-based networks raises the following issues:
•
•
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:
•
•
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).
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
29-2
Legacy Cisco IP Phone—Uses a Cisco proprietary discovery method to detect an IP phone and uses
"link disconnect" to verify an IP phone has been removed from the network
Cisco/IEEE 802.3af compliant—Uses enhanced Cisco Discovery Protocol (CDP) and /or IEEE
802.3af to discover and remove an IP phone
Third party IEEE 802.3af compliant—Uses IEEE 802.3af specified "detection of phone" to detect
an IP phone and "detection of phone removed" to verify that an IP phone has been removed from
the network.
Port 1 connects to the switch or other device that supports VoIP.
Port 2 is an internal 10/100 interface that carries the phone traffic.
Port 3 connects to a PC or other device.
shows one way to configure an IP Phone.
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.
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)
IP Phone
IP
Chapter 29
Configuring VoIP
PC
—
Release 8.1
78-15486-01
- Quick Links:
- Configuration Guide
- Catalyst 2980G Switch
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