Configuring Traffic Policing, Traffic Shaping, And Line Rate; Traffic Evaluation And Token Buckets - HP A6600 Configuration Manual

Configuring traffic policing, traffic shaping, and
line rate
Traffic policing, traffic shaping, and rate limit are QoS technologies that help assign network resources, such
as bandwidth. These technologies increase network performance and user satisfaction. For example,
configure a flow to use only the resources committed to it in a certain time range, which avoids network
congestion caused by burst traffic.
Traffic policing and GTS limit traffic rate and resource usage according to traffic specifications. Once a
particular flow exceeds its specifications, such as bandwidth, it is shaped or policed to ensure it conforms to
the specifications. Token buckets are typical tools for evaluating traffic specifications.

Traffic evaluation and token buckets

Token bucket features
A token bucket is analogous to a container that holds a certain number of tokens. Each token represents a
certain forwarding capacity. The system puts tokens into the bucket at a constant rate. When the token bucket
is full, the extra tokens cause the token bucket to overflow.
Evaluating traffic with the token bucket
A token bucket mechanism evaluates traffic by looking at the number of tokens in the bucket. If the number
of tokens in the bucket is enough for forwarding the packets, the traffic conforms to the specification, and is
called ―conforming traffic.‖ Otherwise, the traffic does not conform to the specification, and is called ―excess
traffic.‖
A token bucket has the following configurable parameters:
Mean rate at which tokens are put into the bucket, which is the permitted average rate of traffic. It is

usually set to the CIR.
Burst size or the capacity of the token bucket. It is the maximum traffic size permitted in each burst, and

is usually set to the CBS. The set burst size must be greater than the maximum packet size.
Each arriving packet is evaluated. In each evaluation, if the number of tokens in the bucket is enough, the
traffic conforms to the specification and the tokens for forwarding the packet are taken away; if the number
of tokens in the bucket is not enough, the traffic is excessive.
Complicated evaluation
Set two token buckets, bucket C and bucket E, to evaluate traffic in a more complicated environment and
achieve more policing flexibility. For example, traffic policing uses the following parameters:
CIR―Rate at which tokens are put into bucket C. It sets the average packet transmission or forwarding

rate allowed by bucket C.
CBS―Size of bucket C, which specifies the transient burst of traffic bucket C can forward.

EBS―Size of bucket E, which specifies the transient burst of traffic bucket E can forward.

33