Huawei v200r001 user manual Introduction to CAR, II.Traffic Measuring with Token Bucket

User Manual - Configuration Guide (Volume 3)	Chapter 2
Versatile Routing Platform	Traffic Classification and Policing

II.Traffic Measuring with Token Bucket

Whether the total number of Tokens in Token Bucket meet the packet forwarding requirement is the basis to evaluate the traffic size. If there are enough Token to forward the packets (usually one Token is associated with the forwarding authority of one bit), the traffic does not exceed the specification; otherwise, the traffic exceeds the specification.

There are main three parameters to evaluate the traffic:

zAverage speed: the speed of Token put into Token Bucket. It is usually set to CIR (Committed Information Rate), that is, allowed average flow speed.

zBurst size: the capacity of the Token Bucket. It is usually set to CBS (Committed Burst Size), that is, the allowed maximum traffic during the evaluation time interval. Burst size must be greater than the longest packet.

zTime Interval: evaluate the traffic every other cycle. It is set by the system. If there are enough Tokens for the packets, it is evaluated as “confirming”. If there are not enough Tokens, it is “not conforming”. “Conforming” indicates that the traffic does not exceed the specification and corresponding number of Tokens that conform to packet forwarding authority will be taken out from the Bucket; “not conforming” indicates that the traffic exceeds the specification and too many Tokens have been consumed.

IIIComplicacy Evaluation

If there is only one Token Bucket, the evaluation result falls into two types: conforming and not conforming.

In order to evaluate more complicated situation and implement more flexible control policy, two Token Buckets will be set. For example, there are 3 parameters in CAR.

CIR(Committed Information Rate)

CBS(Committed Burst Size)

EBS(Excess Burst Size)

The two Token Buckets used transceives Tokens at the same speed of CIR, but with different size--CBS and EBS respectively (CBS is less than EBS. The two Buckets are called C and B.) CBS and EBS are different burst level allowed. The evaluation results in the three cases (that is, sufficient Tokens in C, insufficient Tokens in C but sufficient in D, and sufficient Tokens in neither C nor D), the results are “conforming, partly conforming and not conforming” respectively.

2.1.3 Introduction to CAR

CAR provides classification service and traffic policing by limiting the speed. The user can set IP precedence of the packets coming into the network with CAR classification in order to divide the traffic into multiple precedence levels and service types. The other network equipment can process the data according to the modified IP precedence.

The user can be defined as 6 types of services according to the precedence field of ToS segment in IP packet header. The rule to define the type of packets can be based on multiple criterion, including physical port, source IP address, source MAC address, destination IP address, destination MAC address, application port, IP protocol type or other criterion which can perform classification by using access list or extended access list. Packets can also be classified according to the situation outside the network (i.e., the client type). The network can accept or ignore the classification or reclassify the packets according to a certain rule.

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