Traffic Prioritization and your Switch 55
How traffic is processed to provide Quality of Service
A received packet at the ingress port is checked for its DSCP and IEEE
802.1D attributes to determine the level of service that the packet should
receive.
802.1D packets are categorized into the 8 traffic classes defined by IEEE
802.1D; the higher the class the higher the priority given the packet on
transmission.
DSCP packets are categorized into the six service levels as shown in
Figure 14 and mapped to the appropriate queue.
The priority defined in the service level directs the packet to the
appropriate egress queue. When a packet comes in with both 802.1D
and DSCP priority markings, the higher of the priorities will be used.
Received packets in the Switch 4200 Family are only checked for DSCP
and 802.1D attributes. No other attributes are supported.
Traffic queues are preset on a per-unit basis on the Switch 4200 Family.
Configuring traffic prioritization for QoS on a 4200 Family
QoS can be configured on your Switch using the 3Com Network
Supervisor or via the Command Line Interface (CLI).
You can also configure QoS via the command line interface (CLI). For a
detailed description of the commands that you require, refer to the
Management Interface Reference Guide supplied in HTML format on the
CD-ROM that accompanies your Switch.
Configure Quality of service in the Switch 4200 Family in the following
way:
1 Apply Traffic classification First identify the types of traffic requiring
special treatment. These types are defined in the QoS feature through the
creation of classifiers. The Switch 4200 Family supports two types of
packet attributes on which to classify incoming traffic, Differentiated
Services Code Point (DSCP) and IEEE 802.1D.
2 Identify Service Levels You must then identify the level of service each
classifier should receive. Note that DSCP service levels will be set
somewhere else in the network and not in the Switch 4200 Family. Note
also that 802.1D service levels are fixed and cannot be altered.
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