Cisco Ip Phone Voice Traffic - Cisco 6500 Series Software Configuration Manual

Understanding Cisco IP Phone Support
Figure 11-1 Cisco IP Phone Connected to a Switch
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
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 switch to send Cisco Discovery Protocol version 2
(CDPv2) 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 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
11-2
Cisco Router
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 11 Configuring Cisco IP Phone Support
Workstation/PC
Chapter 31, "Configuring PFC
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