3Com Switch 8800 Advanced Software V5 Configuration Guide

832 CHAPTER 61: TRAFFIC CLASSIFICATION AND TRAFFIC SHAPING CONFIGURATION
Figure 247 DS field and ToS byte
As shown in Figure 247, the ToS byte of IP header contains 8 bits: the first three
bits (0 to 2) indicates IP precedence, valued in the range 0 to 7; the following 4
bits (3 to 6) indicates ToS priority, valued in the range 0 to 15. In RFC2474, the ToS
field of IP packet header is redefined as DS field, where the DiffServ code point
(DSCP) priority is indicated by the first 6 bits (0 to 5), valued in the range 0 to 63.
The remaining 2 bits (6 and 7) are reserved.
Traffic Shaping
Overview
If no restrictions are imposed on the traffics from the users, bursting data sent by
mass users continuously will make the network become more congested. Thus for
more efficient network function and better network service for more users, the
traffics from the users must be restricted, for example, to restrict a traffic can only
acquire the specific assigned resources in certain time interval so as to prevent the
network congestion caused by excess burst.
Traffic shaping is a traffic monitoring policy to restrict 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 shaping. Then based
upon the evaluation result you can implement a regulation policy. Usually, Token
Bucket is used to value the traffic specification.
Traffic Evaluation and
Token Bucket
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.