Cisco Ip Phone Voice Traffic - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Understanding Cisco IP Phone Support
Figure 14-1
Figure 14-1
10/100 module
Catalyst switch or

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
PFC
You can configure the ports on WS-X6548-RJ-45 and WS-X6548-RJ-21 switching modules to trust
Note
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 switch to send Cisco Discovery Protocol (CDP) packets
that instruct an attached Cisco IP phone to transmit voice traffic to the switch in any of the following
ways:
•
•
•
In all configurations, the voice traffic carries a Layer 3 IP precedence value (the default is 5 for voice
Note
traffic and 3 for voice control traffic).
You cannot use Cisco IOS software commands to configure the frame type used by data traffic sent from
a device attached to the access port on the Cisco IP phone.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
14-2
shows a Cisco IP phone connected between a switch and a PC.
Cisco IP Phone Connected to a Switch
Cisco Router
QoS").
In the voice VLAN, tagged with a Layer 2 CoS priority value
In the access VLAN, tagged with a Layer 2 CoS priority value
In the access VLAN, untagged (no Layer 2 CoS priority value)
Cisco IP Phone 7960
Phone
ASIC
P2
3-port
P1
P3
switch
Access
port
Chapter 14 Configuring Cisco IP Phone Support
Workstation/PC
Chapter 38, "Configuring
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