Operation Manual – QoS
H3C S3610&S5510 Series Ethernet Switches
Chapter 2 Traffic Classification, TP, and TS
Configuration
2-6
2.3.2 Evaluating the traffic with the token bucket
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:
z
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).
z
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.
2.3.3 Complicated evaluation
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:
z
CIR
z
CBS
z
Peak information rate (PIR)
z
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 implement different
regulation policies in different conditions, including “enough tokens in C bucket”,
“insufficient tokens in C bucket but enough tokens in E bucket” and “insufficient tokens
in both C bucket and E bucket”.
2.3.4 TP
The typical application of TP is to supervise the specification of certain traffic into the
network and limit it within a reasonable range, or to "discipline" the extra traffic. In this
way, the network resources and the interests of the operators are protected. For
example, you can limit HTTP packets to be within 50% of the network bandwidth. If the
