3com 2928 Betriebsanweisung

 

2-9 

Evaluate traffic with the token bucket 

Token 

bucket

Packets dropped

Packet 

classification

Packets to be sent 

through this interface

Packets sent

Tokens are put into the 

bucket at the set rate

 

 
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 (generally, one token is associated with a 1-bit forwarding authority), the traffic conforms to the 
specification, and the traffic is called conforming traffic; otherwise, the traffic does not conform to the 
specification, and the traffic is called excess traffic.  
A token bucket has the following configurable parameters: 

z

 

Mean rate: At which tokens are put into the bucket, namely, the permitted average rate of traffic. It 
is usually set to the 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 usually set to the committed burst size (CBS). The set burst size must be greater 
than the maximum packet size.  

One evaluation is performed on each arriving packet. In each evaluation, if the number of tokens in the 
bucket is enough, the traffic conforms to the specification and the corresponding tokens for forwarding 
the packet are taken away; if the number of tokens in the bucket is not enough, it means that too many 
tokens have been used and the traffic is excessive.  

With line rate configured on an interface, all packets to be sent through the interface are firstly handled 
by the token bucket of line rate. If there are enough tokens in the token bucket, packets can be 
forwarded; otherwise, packets are put into QoS queues for congestion management. In this way, the 
traffic passing the physical interface is controlled.