Prerequisites For Configuring Modular Qos Congestion Avoidance; Information About Configuring Modular Qos Congestion Avoidance; Random Early Detection And Tcp; Queue-Limit For Wred - Cisco ASR 9000 Series Configuration Manual

Prerequisites for Configuring Modular QoS Congestion Avoidance

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Prerequisites for Configuring Modular QoS Congestion
Avoidance
This prerequisite is required for configuring QoS congestion avoidance on your network:
You must be in a user group associated with a task group that includes the proper task IDs. The command
reference guides include the task IDs required for each command. If you suspect user group assignment is
preventing you from using a command, contact your AAA administrator for assistance.
Information About Configuring Modular QoS Congestion
Avoidance

Random Early Detection and TCP

The Random Early Detection (RED) congestion avoidance technique takes advantage of the congestion control
mechanism of TCP. By randomly dropping packets prior to periods of high congestion, RED tells the packet
source to decrease its transmission rate. Assuming the packet source is using TCP, it decreases its transmission
rate until all packets reach their destination, indicating that the congestion is cleared. You can use RED as a
way to cause TCP to slow transmission of packets. TCP not only pauses, but it also restarts quickly and adapts
its transmission rate to the rate that the network can support.
RED distributes losses in time and maintains normally low queue depth while absorbing traffic bursts. When
enabled on an interface, RED begins dropping packets when congestion occurs at a rate you select during
configuration.

Queue-limit for WRED

Queue-limit is used to fine-tune the number of buffers available for each queue. It can only be used on a
queuing class. Default queue limit is 100 ms of the service rate for the given queue. The service rate is the
sum of minimum guaranteed bandwidth and bandwidth remaining assigned to a given class either implicitly
or explicitly.
The queue-limit is rounded up to one of the following values: 8 KB, 16 KB, 24 KB, 32 KB, 48 KB, 64 KB,
96 KB, 128 KB, 192 KB, 256 KB, 384 KB, 512 KB, 768 KB, 1024 KB, 1536 KB, 2048 KB, 3072 KB, 4196
KB, 8192 KB, 16394 KB, 32768 KB, 65536 KB, 131072 KB, or 262144 KB.
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
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Prerequisites for Configuring Modular QoS Congestion Avoidance, page 40
Information About Configuring Modular QoS Congestion Avoidance, page 40
Additional References, page 49
Configuring Modular QoS Congestion Avoidance