196 Chapter 6: QoS Features Available on the Catalyst 2950 and 3550 Family of Switches
This configuration assists in avoiding congestion on a per-queue basis. Finally, the wrr-
queue cos-map 4 5 configuration informs the switch to map CoS 5 traffic to transmit queue 4.
Because CoS 5 traffic usually represents VoIP traffic, the ideal situation is to transmit the
traffic with strict priority.
Summary
The Catalyst 2950 Family of switches provides for a wide range of QoS features suited
specifically for access layer implementation. You can summarize QoS feature support on
the Catalyst 2950 Family of switches as follows:
• Classification, marking, and policing require the EI software.
• Support exists for classification based on port CoS configuration, trusting
configuration, and ACLs.
• Per-port ingress policing is supported.
• DSCP-to-CoS mapping table is configurable on a global basis.
• Output scheduling uses strict-priority queuing by default.
• WRR scheduling is configurable as an alternative to strict-priority queuing.
The Catalyst 3550 Family of switches provides for a wide range of QoS features suited
specifically for access layer and distribution layer implementation. You can summarize QoS
feature support on the Catalyst 3550 Family of switches as follows:
• No QoS feature differences exist between SMI and EMI software versions.
• Support exists for classification based on port CoS configuration, trusting
configuration, and ACLs.
• Ingress and egress policing is supported on individual interfaces.
• A variant of VLAN-based policing exists as per-port VLAN-based policing.
• The DSCP-to-CoS mapping table is configured on a per-interface basis.
• Congestion management uses WRR with a strict-priority queuing option.
• Congestion avoidance utilizes the tail-drop and WRED techniques.
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