Srr Shaping And Sharing - Cisco WS-C3750-48PS-S Software Configuration Manual

Understanding QoS
Figure 32-6 WTD and Queue Operation
CoS 6-7
CoS 4-5
CoS 0-3
For more information, see the
Thresholds" section on page
Egress Queue-Set" section on page
and to a Threshold ID" section on page

SRR Shaping and Sharing

Both the ingress and egress queues are serviced by SRR, which controls the rate at which packets are
sent. On the ingress queues, SRR sends packets to the stack ring. On the egress queues, SRR sends
packets to the egress port.
You can configure SRR on egress queues for sharing or for shaping. However, for ingress queues, sharing
is the default mode, and it is the only mode supported.
In shaped mode, the egress queues are guaranteed a percentage of the bandwidth, and they are
rate-limited to that amount. Shaped traffic does not use more than the allocated bandwidth even if the
link is idle. Shaping provides a more even flow of traffic over time and reduces the peaks and valleys of
bursty traffic. With shaping, the absolute value of each weight is used to compute the bandwidth
available for the queues.
In shared mode, the queues share the bandwidth among them according to the configured weights. The
bandwidth is guaranteed at this level but not limited to it. For example, if a queue is empty and no longer
requires a share of the link, the remaining queues can expand into the unused bandwidth and share it
among them. With sharing, the ratio of the weights controls the frequency of dequeuing; the absolute
values are meaningless.
For more information, see the
page
"Configuring SRR Shared Weights on Egress Queues" section on page
Catalyst 3750 Switch Software Configuration Guide
32-12
100%
60%
40%
"Mapping DSCP or CoS Values to an Ingress Queue and Setting WTD
32-56, the
"Allocating Bandwidth Between the Ingress Queues" section on
32-58, the "Configuring SRR Shaped Weights on Egress Queues" section on page
1000
600
400
0
"Allocating Buffer Space to and Setting WTD Thresholds for an
32-60, and the "Mapping DSCP or CoS Values to an Egress Queue
32-62.
Chapter 32 Configuring QoS
32-64, and the
32-65.
78-16180-02