3Com S7906E - Switch, Руководство по настройке

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Traffic Policing, Traffic Shaping, and Line Rate
Configuration
When configuring traffic classification, traffic policing, and traffic shaping, go to these sections for
information you are interested in:
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Traffic Policing, Traffic Shaping, and Line Rate Overview
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Configuring Traffic Policing
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Configuring GTS
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Configuring the Line Rate
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Displaying and Maintaining Traffic Policing, GTS, and Line Rate
Traffic Policing, Traffic Shaping, and Line Rate Overview
Without limits on user traffic, a network can be overwhelmed very easily. To help assign network
resources such as bandwidth efficiently to improve network performance and hence user satisfaction,
QoS technologies such as traffic policing, traffic shaping, and rate limit were introduced. For example,
you can configure a flow to use only the resources committed to it in a certain time range, thus avoiding
network congestion caused by burst traffic.
Traffic policing and generic traffic shaping (GTS) limit traffic rate and resource usage according to traffic
specifications. Once a particular traffic exceeds its specifications such as bandwidth assigned to it, it is
shaped or policed to ensure that it is under the specifications. Generally, token buckets are used to
evaluate traffic specifications.
Traffic Evaluation and Token Buckets
Token bucket features
A token bucket is analogous to a container holding a certain number of tokens. The system puts tokens
into the bucket at a set rate. When the token bucket is full, the extra tokens overflows.
Evaluating traffic with the token bucket
The evaluation of traffic specifications is based on whether the number of tokens in the bucket can
meet the need of packet forwarding. Generally, one token is associated with a 1-bit forwarding authority.
If the number of tokens in the bucket is enough for forwarding the packets, the traffic conforms to the
specification and is called conforming traffic; otherwise, the traffic does not conform to the specification
and is called excess traffic.
A token bucket has the following configurable parameters:
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Mean rate: At which tokens are put into the bucket, namely, the permitted average rate of traffic. It
is usually set to the committed information rate (CIR).
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Burst size: the capacity of the token bucket, namely, the maximum traffic size that is permitted in
each burst. It is usually set to the committed burst size (CBS). The set burst size must be greater
than the maximum packet size.