Specifications

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Catalyst 2970 Switch Software Configuration Guide
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Chapter 27 Configuring QoS
Configuring Standard QoS
Configuring Egress Queue Characteristics
Depending on the complexity of your network and your QoS solution, you might need to perform all of
the tasks in the next sections. You will need to make decisions about these characteristics:
• Which packets are mapped by DSCP or CoS value to each queue and threshold ID?
• What drop percentage thresholds apply to the queue-set (four egress queues per port), and how much
reserved and maximum memory is needed for the traffic type?
• How much of the fixed buffer space is allocated to the queue-set?
• Does the bandwidth of the port need to be rate limited?
• How often should the egress queues be serviced and which technique (shaped, shared, or both)
should be used?
These sections describe how to configure egress queue characteristics:
• Configuration Guidelines, page 27-57
• Allocating Buffer Space to and Setting WTD Thresholds for an Egress Queue-Set, page 27-58
(optional)
• Mapping DSCP or CoS Values to an Egress Queue and to a Threshold ID, page 27-60 (optional)
• Configuring SRR Shaped Weights on Egress Queues, page 27-61 (optional)
• Configuring SRR Shared Weights on Egress Queues, page 27-62 (optional)
• Configuring the Egress Expedite Queue, page 27-63 (optional)
• Limiting the Bandwidth on an Egress Interface, page 27-64 (optional)
Configuration Guidelines
Follow these guidelines when the expedite queue is enabled or the egress queues are serviced based on
their SRR weights:
• If the egress expedite queue is enabled, it overrides the SRR shaped and shared weights for queue 1.
• If the egress expedite queue is disabled and the SRR shaped and shared weights are configured, the
shaped mode overrides the shared mode for queue 1, and SRR services this queue in shaped mode.
• If the egress expedite queue is disabled and the SRR shaped weights are not configured, SRR
services this queue in shared mode.