3Com Switch 7754, Configuration Manual

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662 C
HAPTER
61: Q
O
S C
ONFIGURATION
Figure 173 Evaluate the traffic with the token bucket
1 Evaluate the traffic with the token bucket
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 is conforming to the
specification, and otherwise the traffic is nonconforming or excess.
When the token bucket evaluates the traffic, its parameter configurations include:
■
Average rate: The rate at which tokens are put into the bucket, namely, the
permitted average rate of the traffic. It is generally set to committed
information rate (CIR).
■
Burst size: The capacity of the token bucket, namely, the maximum traffic size
that is permitted in every burst. It is generally set to committed burst size (CBS).
The set burst size must be bigger than the maximum packet length.
One evaluation is performed on each arriving packet. In each evaluation, if the
number of tokens in the bucket is enough, the traffic is conforming to the
specification and you must take away some tokens whose number is
corresponding to the packet forwarding authority; if the number of tokens in the
bucket is not enough, it means that too many tokens have been used and the
traffic is excess.
2 Complicated evaluation
You can set two token buckets in order to evaluate more complicated conditions
and implement more flexible regulation policies. For example, TP includes 4
parameters:
■
CIR
■
CBS
■
Peak information rate (PIR)
■
Excess burst size (EBS)
Token
bucket
Drop
Packet
classification
Packets to be sent
through this port
Continue
to send
Put tokens in the bucket at the
set rate