3Com MSR 50 Series Configuration Manual page 1629

Figure 459 Measuring the traffic with Token Bucket
Measuring the traffic with Token Bucket
Whether or not the token quantity of the Token Bucket can satisfy the packets
forwarding is the basis for Token Bucket to measure the traffic specification. If
enough tokens are available for forwarding packets, traffic is regarded conforming
the specification (generally, one token is associated to the forwarding ability of
one bit), otherwise, non-conform or excess.
When measuring the traffic with Token Bucket, these parameters are included:
Mean rate: The rate of putting Token into Bucket, i.e. average rate of the
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permitting traffic. Generally set as CIR (Committed Information Rate).
Burst size: Token Bucket's capability, i.e. the maximum traffic size of every
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burst. Generally, it is set as CBS (Committed Burst Size), and the bursting size
must be greater than the maximum packets size.
A new evaluation will be made when a new packet arrives. If there are enough
tokens in bucket for each evaluation, it shows that traffics are within the bound,
and at this time the amount of tokens appropriate for the packets forwarding
rights, need to be taken out. Otherwise, it shows that too many tokens have been
used, and traffic specifications are exceeded.
Complicated evaluation
Two Token Buckets can be configured to evaluate conditions that are more
complex and to implement more flexible regulation policy. For example, Traffic
Policing (TP) has three parameters, as follows:
CIR (Committed Information Rate)
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CBS (Committed Burst Size)
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EBS (Excess Burst Size)
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It uses two Token Buckets with the token-putting rate of every bucket set as CIR
equally, but with different capabilities: CBS and EBS (CBS < EBS, called C Bucket
Traffic Evaluation and Token Bucket 1629