represents how a policer is implemented using the token bucket
algorithm. The token allocator allocates tokens to the policer based on the configured
bandwidth limit, which is the token size multiplied by the token arrival rate.
token size x token arrival rate = policer rate (configured bandwidth limit)
Figure 3: Token Bucket Algorithm
Token Allocator
Token Bucket
Incoming
Packet
g041264
Outgoing
Packet
When a packet arrives at an interface configured with a policer, tokens that represent
the number of bits that correspond to the length of the packet are used (or “cashed in”)
from the token bucket. If the token arrival rate is higher than the rate of traffic so that
there are tokens not being used, the token bucket is filled to capacity, and arriving tokens
“overflow” the bucket and are lost. The token bucket depth represents the single
user-configured burst size for the policer.
If there are tokens in the token bucket and the incoming traffic rate is higher than the
token rate (the configured policer rate, bandwidth limit), the traffic can use the tokens
until the bucket is empty. The token consumption rate can be as high as the incoming
traffic rate, which creates the burst of traffic shown in
By using the token bucket algorithm, the average bandwidth rate being allowed is close
to the configured bandwidth limit while simultaneously supporting bursty traffic, as
shown in
Figure 4: Traffic Behavior Using Policer and Burst Size
Traffic
Volume
Bandwidth Limit
Time
Unused
Tokens
Unused
Tokens
Unused
Tokens
g041265
Bursts use
unused tokens
27
Copyright © 2016, Juniper Networks, Inc.
Chapter 5: Implementing Traffic Policers on EX 9200 Switches
Содержание EX9200 Series
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