IBM RackSwitch G8000, Application Manual

Page: 133 / 362

© Copyright IBM Corp. 2011
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Chapter 11. Quality of Service
Quality of Service features allow you to allocate network resources to
mission-critical applications at the expense of applications that are less sensitive to
such factors as time delays or network congestion. You can configure your network
to prioritize specific types of traffic, ensuring that each type receives the appropriate
Quality of Service (QoS) level.
The following topics are discussed in this section:
•
“QoS Overview” on page 131
• “Using ACL Filters” on page 133
• “Using DSCP Values to Provide QoS” on page 134
• “Using 802.1p Priority to Provide QoS” on page 140
• “Queuing and Scheduling” on page 141
QoS Overview
QoS helps you allocate guaranteed bandwidth to the critical applications, and limit
bandwidth for less critical applications. Applications such as video and voice must
have a certain amount of bandwidth to work correctly; using QoS, you can provide
that bandwidth when necessary. Also, you can put a high priority on applications
that are sensitive to timing out or that cannot tolerate delay, by assigning their traffic
to a high-priority queue.
By assigning QoS levels to traffic flows on your network, you can ensure that
network resources are allocated where they are needed most. QoS features allow
you to prioritize network traffic, thereby providing better service for selected
applications.
Figure 15 shows the basic QoS model used by the switch.
Figure 15. QoS Model
The basic QoS model works as follows:
•
Classify traffic:
– Read DSCP value.
– Read 802.1p priority value.
– Match ACL filter parameters.
Ports
ACL
Filter
Permit/Deny
Classify
Packets
Perform
Actions
Egress
Ingress
COS
Queue
Queue and
Schedule