3Com MSR 50 Series Configuration Manual page 1711

Figure 488 Fundamentals of FR class token bucket
In the token bucket approach, a packet requiring traffic control is put into the
token bucket for processing before transmission. If enough tokens are available in
the token bucket for sending the packet, the packet will be allowed to pass, that
is, the packet will be sent normally. If the number of tokens is not enough, the
packet will be put in the FR class queue. Once enough tokens are collected in the
token bucket, the packet will be taken out of the queue for transmission. In this
way, you can control the traffic size of some type of packets. Tokens are in the unit
of bit.
Following are the meanings of the FR protocol-provisioned parameters when they
are applied in the FRTS implementation:
The sum of CBS and EBS equals the token bucket size.
■
CIR ALLOW defines the number of tokens put into the token bucket per
■
second.
For efficiency sake, the FRTS solution introduced the concept of dynamic Tc. Tc
(Tc=size of packet/CIR) is in the range of 10 to 100 milliseconds, and allows of
dynamic adjustment depending on the transmitted packet size. That is, the device
will distribute the required tokens to the packet waiting for transmission within
the current Tc regardless of the packet size (which is smaller than 1500 bytes).
Figure 489 Relationship between Tc and CIR
Tc(ms)
15
10
5
400 800
Frame Relay QoS Overview
K=1/CIR
Size of packet (byte)
1200
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