Traffic Evaluation And Token Bucket - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
Traffic policing and traffic shaping is a traffic monitoring policy to adjust the traffic and
resources through comparing with the traffic specification. To know whether the traffic
exceeds the specification or not is a prerequisite for traffic policing or shaping. Then
based upon the evaluation result you can implement a regulation policy. Usually Token
Bucket is used to value the traffic specification.

2.2.1 Traffic Evaluation and Token Bucket

I. Token bucket features
Token Bucket can be regarded as a container to reserve Token, which has certain
capacity. The system will put Tokens into the Bucket at a defined rate. In case the
Bucket is full, the extra Tokens will overflow and no more Tokens will be added.
incoming packets
Figure 2-1 Measuring the traffic with Token Bucket
II. 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
permitting traffic. Generally set as CIR (Committed Information Rate).
Burst size: Token Bucket's capability, i.e. the maximum traffic size of every 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
Tokens enter bucket
at the given speed
classify
3Com Corporation
2-2
Chapter 2 Traffic Classification, Policing, and Shaping
outgoing packets
Token Bucket
Discarded
packets