Brocade Communications Systems 53-1001761-01 manual Scheduling, Strict priority scheduling

9 Scheduling

Multicast rate limit is applied to the output of each multicast receive queue. Rate limits apply equally to ingress receive queueing (first level expansion) and egress receive queueing (second level expansion) since the same physical receive queues are utilized. You can set policies to limit the maximum multicast frame rate differently for each traffic class level and cap the total multicast egress rate out of the system.

Multicast rate limiting includes the following features:

•All configuration parameters are applied globally. Multicast rate limits are applied to multicast receive queues as frame replications are placed into the multicast expansion queues. The same physical queues are used for both ingress receive queues and egress receive queues so rate limits are applied to both ingress and egress queueing.

•Four explicit multicast rate limit values are supported, one for each traffic class. The rate limit values represent the maximum multicast expansion rate in packets per second (PPS).

Creating a receive queue multicast rate-limit

Perform the following steps from Privileged EXEC mode to create the receive queue multicast rate-limit.

1. Enter global configuration mode.

switch#configure terminal

2.Create a lower maximum multicast frame expansion rate. In this example, the rate is to 10000 PPS.

switch(config)#qos rcv-queue multicast rate-limit 10000

Example of creating a lower maximum multicast frame expansion rate to 10000pkt/s.

switch:admin>cmsh switch>enable

switch#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

switch(config)#qos rcv-queue multicast rate-limit 10000 switch(config)#end

3. Enter the copy command to save the running-config file to the startup-config file.

switch#copy running-config startup-config

Scheduling

Scheduling arbitrates among multiple queues waiting to transmit a frame. The Brocade 8000 supports both Strict Priority (SP) and Deficit Weighted Round Robin (DWRR) scheduling algorithms. Also supported is the flexible selection of the number of traffic classes using SP-to-DWRR. When there are multiple queues for the same traffic class, then scheduling takes these equal priority queues into consideration.

Strict priority scheduling

Strict priority scheduling is used to facilitate support for latency-sensitive traffic. A strict priority scheduler drains all frames queued in the highest priority queue before continuing on to service lower priority traffic classes. A danger with this type of service is that a queue can potentially starve out lower priority traffic classes.

102	Converged Enhanced Ethernet Administrator’s Guide
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