Cisco Catalyst 2960 Software Configuration Manual page 756

Understanding QoS
Figure 33-8
Receive packet from
(DSCP or CoS value).
Determine egress queue
number and threshold
based on the label.
Queue the packet. Service
the queue according to
Rewrite DSCP and/or
Each port supports four egress queues, one of which (queue 1) can be the egress expedite queue.These
queues are configured by a queue-set. All traffic leaving an egress port flows through one of these four
queues and is subjected to a threshold based on the QoS label assigned to the packet.
Figure 33-9
the reserved pool. The switch uses a buffer allocation scheme to reserve a minimum amount of buffers
for each egress queue, to prevent any queue or port from consuming all the buffers and depriving other
queues, and to control whether to grant buffer space to a requesting queue. The switch detects whether
the target queue has not consumed more buffers than its reserved amount (under-limit), whether it has
consumed all of its maximum buffers (over limit), and whether the common pool is empty (no free
Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
33-18
Queueing and Scheduling Flowchart for Egress Ports
Start
the internal ring.
Read QoS label
Yes
Are thresholds
being exceeded?
No
the SRR weights.
CoS value as
appropriate.
Send the packet
out the port.
Done
shows the egress queue buffer. The buffer space is divided between the common pool and
Drop packet.
Chapter 33 Configuring QoS
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