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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
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Chapter 16 Configuring Cisco IP Phone Support
Understanding Cisco IP Phone Support
Cisco IP Phone Connections
The Cisco IP phone contains an integrated 3-port 10/100 switch. The ports are dedicated connections to
these devices:
•
Port 1 connects to the router.
•
Port 2 is an internal 10/100 interface that carries the Cisco IP phone traffic.
•
Port 3 connects to a PC or other device.
Figure 16-1
shows a Cisco IP phone connected between a router and a PC.
Figure 16-1 Cisco IP Phone Connected to a Switch
Cisco IP Phone Voice Traffic
The Cisco IP phone transmits voice traffic with Layer 3 IP precedence and Layer 2 CoS values, which
are both set to 5 by default. The sound quality of a Cisco IP phone call can deteriorate if the voice traffic
is transmitted unevenly. To provide more predictable voice traffic flow, you can configure QoS to trust the
Layer 3 IP precedence or Layer 2 CoS value in the voice traffic (refer to
Chapter 41, “Configuring
PFC QoS”
).
Note
You can configure the ports on WS-X6548-RJ-45 and WS-X6548-RJ-21 switching modules to trust
received Layer 2 CoS values (QoS port architecture 1p1q0t/1p3q1t). The WS-X6548-RJ-45 and
WS-X6548-RJ-21 switching modules cannot supply power to Cisco IP phones. Configure QoS policies
that use the Layer 3 IP precedence value on other switching modules.
You can configure a Layer 2 access port with an attached Cisco IP phone to use one VLAN for voice
traffic and another VLAN for data traffic from a device attached to the Cisco IP phone.
You can configure Layer 2 access ports on the router to send Cisco Discovery Protocol (CDP) packets
that instruct an attached Cisco IP phone to transmit voice traffic to the router in any of the following
ways:
•
In the voice VLAN, tagged with a Layer 2 CoS priority value
•
In the access VLAN, tagged with a Layer 2 CoS priority value
3-port
switch
P1
P3
P2
Access
port
Cisco IP Phone 7960
Workstation/PC
Catalyst switch or
Cisco Router
10/100 module
79490
Phone
ASIC