3Com Switch 4800G 24-Port Configuration Manual page 865

Evaluating Traffic with a
Token Bucket
Complicated Evaluation
Figure 259 Evaluate traffic with a token bucket
Put tokens in the bucket at the
Packets to be sent
through this port
Packet
classification
The evaluation for the traffic specification is based on whether the number of
tokens in the bucket can meet the need of packet forwarding. If the number of
tokens in the bucket is enough to forward the packets, the traffic is conforming to
the specification; otherwise, the traffic is nonconforming or excess.
When the token bucket evaluates the traffic, its parameter configurations include:
Average rate: The rate at which tokens are put into the bucket, namely, the
■
permitted average rate of the traffic. It is generally set to committed
information rate (CIR).
Burst size: The capacity of the token bucket, namely, the maximum traffic size
■
that is permitted in each burst. It is generally set to committed burst size (CBS).
The set burst size must be greater than the maximum packet length.
An evaluation is performed on the arrival of each packet. In each evaluation, if the
bucket has enough tokens for use, the traffic is controlled within the specification
and a number of tokens equivalent to the packet forwarding authority must be
taken out; otherwise, this means too many tokens have been used - the traffic is in
excess of the specification.
You can set two token buckets in order to evaluate more complicated conditions
and implement more flexible regulation policies. For example, TP uses four
parameters:
CIR
■
CBS
■
Peak information rate (PIR)
■
Excess burst size (EBS)
■
Two token buckets are used in this evaluation. Their rates of putting tokens into
the buckets are CIR and PIR respectively, and their sizes are CBS and EBS
respectively (the two buckets are called C bucket and E bucket respectively for
short), representing different permitted burst levels. In each evaluation, you can
Traffic Evaluation and Token Bucket
set rate
Continue
to send
Token
bucket
Drop
865