Traffic Policing And Line Rate Configuration; Traffic Policing And Line Rate Overview; Traffic Evaluation And Token Buckets - 3Com 4500G Family Configuration Manual

4

Traffic Policing and Line Rate Configuration

When configuring traffic policing and line rate, go to these sections for information you are interested in:

Traffic Policing and Line Rate Overview

Configuring Traffic Policing
Configuring the Line Rate
Displaying and Maintaining Traffic Policing, GTS, and Line Rate
Traffic Policing 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 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 line rate 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 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:
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).
Burst size or the capacity of the token bucket. It is 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.
Evaluation is performed for each arriving packet. In each evaluation, if the number of tokens in the
bucket is enough, the traffic conforms to the specification and the tokens for forwarding the packet are
taken away; if the number of tokens in the bucket is not enough, the traffic is excessive.
4-1