Queueing And Scheduling On 10/100 Ethernet Ports - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 29 Configuring QoS

Queueing and Scheduling on 10/100 Ethernet Ports

Figure 29-6
Figure 29-6 Queueing and Scheduling Flowchart for 10/100 Ethernet Ports
Get minimum-reserve level
Put packet into specified
queue and service queue
If the expedite queue is enabled, WRR services it until it is empty before servicing the other three
Note
queues.
During the queueing and scheduling process, the switch uses egress queues (to select the
minimum-reserve level and buffer size) and WRR for congestion management.
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 29-7
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 assigned 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. You assign the minimum-reserve level to a queue
by using the wrr-queue min-reserve interface configuration command.
78-11194-09
shows the queueing and scheduling flowchart for 10/100 Ethernet ports.
Start
Read the CoS value of
CoS-to-queue map.
Queue number
and queue size.
Is space No
available?
Yes
according to WRR.
Done
is an example of the 10/100 Ethernet port queue assignments, minimum-reserve levels, and
Drop packets until
space is available.
Catalyst 3550 Multilayer Switch Software Configuration Guide
Understanding QoS
29-15