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Class of Service Configuration
Class of Service (CoS) allows you to specify which data packets have
greater precedence when traffic is buffered in the switch due to
congestion. This switch supports CoS with four egress (output) queues for
each port. Data packets in a port’s high-priority queue will be transmitted
before those in the lower-priority queues. The switch forwards packets
onto the network based on traffic classes. The switch places packets into
outgoing queues by mapping each of the eight incoming priority levels to
one of four outgoing traffic classes. (See “Mapping CoS Values to Egress
Queues” on page 2-97.) You can set the default priority for each interface,
and configure the mapping of frame priority tags to the switch’s traffic
classes.
Setting the Default Priority for Interfaces
You can specify the default port priority for each interface on the switch.
All untagged packets entering the switch are tagged with the specified
default port priority, and then sorted into the appropriate egress queue at
the output port.
Command Usage
• This switch provides four egress queues for each port. It uses
Weighted Round Robin to prevent head-of-queue blockage.
• The default priority applies for an untagged frame received on a port
set to accept all frame types (i.e, receives both untagged and tagged
frames). This priority does not apply to IEEE 802.1Q VLAN tagged
frames. If the incoming frame is an IEEE 802.1Q VLAN tagged
frame, the IEEE 802.1p User Priority bits will be used.
• If the output port is an untagged member of the associated VLAN,
these frames are stripped of all VLAN tags prior to transmission.
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