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Chapter 8: Quality of Service Configuration
Quality of Service (QoS) is a general term referring to various methods of traffic management you can employ on
your network to ensure that traffic you identify as high-priority can use a sufficient share of the available bandwidth.
The IC39240/480 internally has 4 COS queues per port with which a wide varieties of applications (Video/Audio) can
be supported.
In QOS, packets are classified by the priority assigned to them. Packets can be assigned a priority in various ways. A
packet can be assigned a priority based on the input port, 802.1P header or ACL. There are 8 priorities 0~7. Each
packet is queued on one of the 4 internal queues based on its priority and queuing configuration. Queue 4 has the
highest priority and queue 1 the lowest.
The IC39240/480 supports the following QoS methods:
• Weighted Round Robin
• 802.1P Priority Queuing
• IP precedence, DSCP and DSCP Remark
• Ingress Rate-Limit and Egress Traffic-Shaping
8.1 Scheduling algorithm
There are 2 methods to schedule a packet to be transmitted from the switch : strict priority, and weighed round robin.
In strict priority, the packet with the highest priority will be sent first, the lower priority packets will be sent only when
all higher priority packets have been sent. Therefore a low priority packet will not be sent if higher priority packets are
present all the time.
In weighed round robin, the higher priority will not be able to hog all the XMT resources. The resources are allocated
based on the weight value associated with each queue. The service of a queue will stop when the resource is used
up. Then the service will go to the next queue. This will proceed with the 4 queues in a round robin fashion.
8.1.1 Configuring Weighted Round Robin
When Weighted Round Robin is enabled, the default settings are as follows:
Queue Weight
1 1
2 2
3 4
4 8
One can change the weights assigned to each queue to alter the service priorities. Based on the default values,
queue 4 will be allocated more resource, hence higher priority.
To set weighted round robin settings, use the following command in EXEC mode:
57 Asante IntraCore IC39240/480 User’s Manual