Brocade Communications Systems 53-1002163-02 manual Configuring QoS, QoS overview

	Chapter
Configuring QoS	11

In this chapter

•QoS overview	107
•Rewriting	108
•Queueing	108
•Congestion control	113
•Multicast rate limiting	116
•Scheduling	117
•CEE map configuration	119

QoS overview

Quality of Service (QoS) provides you with the capability to control how the traffic is moved from switch to switch. In a network that has different types of traffic with different needs (CoS), the goal of QoS is to provide each traffic type with a virtual pipe. FCoE uses traffic class mapping, scheduling, and flow control to provide quality of service.

Traffic running through the switches can be classified as either multicast traffic or unicast traffic. Multicast traffic has a single source but multiple destinations. Unicast traffic has a single source with a single destination. With all this traffic going through inbound and outbound ports, QoS can be set based on egress port and priority level of the CoS.

QoS can also be set on interfaces where the end-station knows how to mark traffic with QoS and it lies with the same trusted interfaces. An untrusted interface is when the end-station is untrusted and is at the administrative boundaries.

The QoS features are:

•Queueing—Queueing provides temporary storage for frames while waiting for transmission. Queues are selected based on ingress ports, egress ports, and configured user priority level.

•Congestion control—When queues begin filling up and all buffering is exhausted, frames are dropped. This has a detrimental effect on application throughput. Congestion control techniques are used to reduce the risk of queue overruns without adversely affecting network throughput. Congestion control features include IEEE 802.3x Ethernet Pause, Tail Drop, and Ethernet Priority Flow Control (PFC).

•Multicast rate limiting—Many multicast applications cannot be adapted for congestion control techniques and the replication of frames by switching devices can exacerbate this problem. Multicast rate limiting controls frame replication to minimize the impact of multicast traffic.

Converged Enhanced Ethernet Administrator’s Guide	107
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