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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
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Chapter 53 Using Automatic QoS
Using the Automatic QoS Macro on the Switch
The priorities for these CoS/DSCP values are as follows:
•
CoS 5
(voice data)
—
Highest priority (priority queue if present, otherwise high queue)
•
CoS 6, 7 (routing protocols)
—
Second priority (high queue)
•
CoS 3, 4 (call signal and video stream)
—
Third priority (high queue)
•
CoS 1, 2 (streaming and mission critical)
—
Fourth priority (high queue)
•
CoS 0
—
Low priority (low queue)
For the ports that do not implement a priority queue, the WRED and tail-drop mechanisms are used to
attain traffic prioritization within the queue. See the
“Global Automatic QoS Detail Settings” section on
page 53-7
for specific scheduling settings.
QoS Scenario—Cisco IP Phone
In most configurations, you can connect the Cisco IP Phone 79xx directly to the Catalyst switch port.
Optionally, you can attach a PC to the phone and use the phone as a hop to the switch.
Typically, the traffic that comes from the phone and enters the switch is marked with a tag using the
802.1Q/p header. The header contains the VLAN information and the CoS 3-bit field. The CoS
determines the priority of the packet. The switch uses the CoS field to distinguish the PC traffic from the
phone traffic. The switch can also use the DSCP field for the same purpose.
In most Cisco IP Phone 79xx configurations, the traffic that comes from the phone and enters the switch
is trusted. You set the port trust to trust-cos to prioritize the voice traffic over other types of traffic in the
network.
The Cisco IP Phone 79xx has a built-in switch that mixes the traffic that comes from the PC, the phone,
and the switch port. The Cisco IP Phone 79xx has the trust and classification capabilities that you need
to configure. For more information, see the
“Port-Specific Automatic QoS Settings—ciscosoftphone”
section on page 53-10
.
QoS Scenario—Cisco SoftPhone
The Cisco SoftPhone is a software product that runs on a standard PC and emulates an IP phone. The
main difference between the Cisco SoftPhone and the Cisco IP Phone 79xx is that the Cisco SoftPhone
marks its voice traffic through a DSCP, while the Cisco IP Phone 79xx marks its traffic through a CoS.
The QoS settings on the switch accommodate this behavior by trusting the Layer 3 marking of the traffic
entering the port. All other behavior is similar to the Cisco IP Phone 79xx.
Using the Automatic QoS Macro on the Switch
These sections describe the automatic QoS macro:
•
Automatic QoS Overview, page 53-4
•
Automatic QoS Configuration Guidelines and Restrictions, page 53-4
•
Global Automatic QoS Macro, page 53-6
•
Port-Specific Automatic QoS Macro, page 53-9
•
CLI Interface for Automatic QoS, page 53-13
•
Detailed Automatic QoS Configuration Statements, page 53-18
