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10-1
v1.0, May 2008
Chapter 10
Class of Service (CoS) Queuing
This section describes the Class of Service (CoS) Queue Mapping and Traffic Shaping features.
Overview
Each port has one or more queues for packet transmission. During configuration, you can
determine the mapping and configuration of these queues.
Based on service rate and other criteria you configure, queues provide preference to specified
packets. If a delay becomes necessary, the system holds packets until the scheduler authorizes
transmission. As queues become full, packets are dropped. Packet drop precedence indicates the
packet’s sensitivity to being dropped during times of queue congestion.
CoS mapping, queue parameters, and queue management are configurable per interface.
Queue management is configurable per interface.
Some hardware implementations allow queue depth management using tail dropping or Weighted
random early discard (WRED).
Some hardware implementations allow queue depth management using tail dropping.
The operation of CoS Queuing involves queue mapping and queue configuration.
CoS Queue Mapping
CoS Queue Mapping uses trusted and untrusted ports.
Trusted Ports
• System takes at face value certain priority designation for arriving packets.
• Trust applies only to packets that have that trust information.
• Can only have one trust field at a time - per port.
– 802.1p User Priority (default trust mode - Managed through Switching configuration)