Configuring Traffic Policing, Traffic Shaping, And Rate Limit; Overview; Traffic Evaluation And Token Buckets - HP 5830 Series Configuration Manual

Configuring traffic policing, traffic shaping,
and rate limit
This chapter describes how to configure traffic policing, traffic shaping, and rate limit.

Overview

Traffic policing, traffic shaping, and rate limit are QoS techniques that help assign network resources,
such as assigning bandwidth. They increase network performance and user satisfaction. For example,
you can configure a flow to use only the resources committed to it in a certain time range. This avoids
network congestion caused by bursty traffic.
Traffic policing and generic traffic shaping (GTS) limit the traffic rate and resource usage according to
traffic specifications. Once a particular flow exceeds its specifications, such as assigned bandwidth, the
flow is shaped or policed to make sure that it is under the specifications. You can use token buckets for
evaluating traffic specifications.

Traffic evaluation and token buckets

This section describes 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 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 committed information rate (CIR).
Burst size or the capacity of the token bucket. It is the maximum traffic size permitted in each burst.
•
It is usually set to the committed burst size (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
You can set two token buckets, bucket C and bucket E, to evaluate traffic in a more complicated
environment and achieve more policing flexibility. Traffic policing uses the following parameters:
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