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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter20 Configuring QoS Understanding QoS
Queueing and Scheduling on 10/100 Ethernet Ports
Figure 20-6 shows the queueing and scheduling flowchart for 10/100 Ethernet ports.
Figure20-6 Queueing and Scheduling Flowchart for 10/100 Ethernet Ports
Note If the expedite queue is enabled, WRR services it until it is empty before servicing the other three
queues.
During the queueing and scheduling process, the switch uses eg ress q ue ues, wh ich sel ect th e
minimum-reserve level and buffer size, and WRR to provide conge stion ma nage ment .
Each 10/100 Ethernet port has four egress queues, one of which can be the egress expedite queue. Each
queue can access one of eight minimum-reserve levels; each level has 100 packets of buffer space by
default for queueing packets. When the buffer specified for the minimum-reserve level is full, packets
are dropped until space is available.
Figure 20-7 is an example of the 10/100 Ethernet port queue assignments, minimum-reserve levels, and
buffer sizes. The figure shows four egress queues per port, with each queue assigned to a
minimum-reserve level. For example, for Fast Ethernet port 0/1, queue 1 is assi gned to minimum-reserve
level 1, queue 2 is assigned to minimum-reserve level 3, queue 3 is assigned to minimum-reserve level
5, and queue 4 is assigned to minimum-reserve level 7. Y ou ass ign the mini mum-reserv e level to a queue
by using the wrr-queue min-reserve interface configuration command.
65128
No
Yes
Queue number
Read the CoS value of
CoS-to-queue map.
Get minimum-reserve level
and queue size.
Is space
available?
Put packet into specified
queue and service queue
according to WRR.
Drop packets until
space is available.
Start
Done