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Cisco Catalyst 3750-X User Manual

Cisco Catalyst 3750-X
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39-20
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 39 Configuring QoS
Understanding QoS
Figure 39-12 Queueing and Scheduling Flowchart for Egress Ports on Catalyst 3560-X Switches
Each port supports four egress queues, one of which (queue 1) can be the egress expedite queue. These
queues are assigned to a queue-set. All traffic exiting the switch flows through one of these four queues
and is subjected to a threshold based on the QoS label assigned to the packet.
Figure 39-13 sho
ws the egress queue buffer. The buffer space is divided between the common pool and
the reserved pool. The switch uses a buffer allocat
ion 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
90565
Receive packet from
the internal ring.
Read QoS label
(DSCP or CoS value).
Determine egress queue
number and threshold
based on the label.
Are thresholds
being exceeded?
Send the packet
out the port.
Queue the packet. Service
the queue according to
the SRR weights.
Drop packet.
Start
Done
Ye s
No
Rewrite DSCP and/or
CoS value as
appropriate.

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Cisco Catalyst 3750-X Specifications

General IconGeneral
Switching Capacity160 Gbps
Stacking Bandwidth64 Gbps
Max Stacking Units9
Layer SupportLayer 2 and Layer 3
Form FactorRack-mountable
DRAM256 MB
Flash Memory64 MB
ModelCisco Catalyst 3750-X Series
Ports24 or 48 10/100/1000 Ethernet ports
Uplink Interfaces4 SFP or 2 SFP+
FeaturesStackWise Plus, EnergyWise
ImageIP Base or IP Services
Operating Temperature0 to 40°C
Operating Humidity10 to 85% noncondensing

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