Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 637

Chapter 38 Configuring PFC QoS
Marking is the process of setting a Layer 3 DSCP value in a packet; in this publication, the definition
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of marking is extended to include setting Layer 2 CoS values. Marking changes the value of a label.
• Packets carry traffic at Layer 3.
Policing is limiting bandwidth used by a flow of traffic. Policing is done on the PFC3B. Policing can
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mark or drop traffic.
• Queues—Queues are allocations of buffer space used to temporarily store data on a port.
• QoS labels—PFC QoS uses CoS, DSCP, and IP Precedence as QoS labels. QoS labels are
prioritization values carried in Layer 3 packets and Layer 2 frames.
• Scheduling is the assignment of Layer 2 frames to a queue. PFC QoS assigns frames to a queue
based on Layer 2 CoS values.
Shaped round robin (SRR) is a dequeuing algorithm.
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• Threshold—Percentage of queue capacity above which traffic is dropped.
• Type of Service (ToS) is a one-byte field that exists in an IP version 4 header that is used to specify
the priority value applied to the packet. The ToS field consists of eight bits. The first three bits
specify the IP precedence value, which can range from zero to seven, with zero being the lowest
priority and seven being the highest priority. The ToS field can also be used to specify a DSCP value.
DSCP is defined by the six most significant bits of the ToS. DSCP values can range from 0 to 63.
Weight—ratio of bandwidth allocated to a queue.
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OL-11439-03
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
PFC QoS Glossary
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