Cos Queuing Concepts; Cos Queue Mapping; Trusted Ports - NETGEAR M4200 Software Administration Manual

CoS Queuing Concepts

Each port has one or more queues for packet transmission. During configuration, you can
determine the mapping and configuration of these queues.
Based on the service rate and other criteria you configure, queues provide preference to
specified packets. If a delay is 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 queue congestion.
You can CoS on a per-interface basis:
• You can configure CoS mapping.
• Queue parameters and queue management are 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

• The system takes at face value certain priority designations for arriving packets.
• Trust applies only to packets that have that trust information.
• There can be only one trust field at a time - per port.
- 802.1p user priority (This is the default trust mode and is managed through switching
configuration.)
- IP precedence
- IP DiffServ Code Point (DSCP)
The system can assign the service level based upon the 802.1p priority field of the L2
header. You configure this by mapping the 802.1p priorities to one of three traffic class
queues. These queues are:
• Queue 2. Minimum of 50 percent of available bandwidth
• Queue 1. Minimum of 33 percent of available bandwidth
• Queue 0. Lowest priority, minimum of 17 percent of available bandwidth
For untagged traffic, you can specify the default 802.1p priority on a per-port basis.
Managed Switches
CoS Queuing
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