Juniper EX9200 Series, Features Manual

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Dual Token Bucket Algorithms
This topic covers the following information:
• Token Bucket Concepts on page 22
•
Guaranteed Bandwidth for Three-Color Marking on page 22
•
Nonconformance Measurement for Single-Rate Three-Color Marking on page 22
• Nonconformance Measurement for Two-Rate Three-Color Marking on page 23
Token Bucket Concepts
When you apply traffic policing to the input or output traffic at an interface, the rate limits
and actions specified in the policer configuration are used to enforce a limit on the average
throughput rate at the interface while also allowing bursts of traffic up to a maximum
number of bytes based on the overall traffic load. Junos OS policers measure traffic-flow
conformance to a policing rate limit by using a
token bucket algorithm . An algorithm based
on a single token bucket allows burst of traffic for short periods, whereas an algorithm
based dual token buckets allows more sustained bursts of traffic.
Guaranteed Bandwidth for Three-Color Marking
A committed information rate (CIR) defines the guaranteed bandwidth for traffic arriving
at or departing from the interface under normal line conditions. A flow of traffic at an
average rate that conforms to the CIR is categorized green, and packets in a green flow
are implicitly marked with
low
packet loss priority (PLP) and then passed through the
interface. During periods of relatively low traffic (traffic that arrives at or departs from
the interface at average rates below the CIR), any unused bandwidth capacity
accumulates in the first token bucket, but only up to a configured number of bytes. If any
unused bandwidth capacity overflows the first bucket, the excess accumulates in a
second token bucket.
The committed burst size (CBS) defines the maximum number of bytes for which unused
amounts of the guaranteed bandwidth can be accumulated in the first token bucket. A
burst of traffic at an average rate that exceeds the CIR is also categorized as green
provided that sufficient unused bandwidth capacity is available in the first token bucket.
Nonconformance Measurement for Single-Rate Three-Color Marking
Single-rate three-color policer configurations specify a second burst size—the excess
burst size (EBS)—that defines the maximum number of bytes for which the second token
bucket can accumulate unused bandwidth that overflows from the first bucket.
A traffic flow is categorized yellow if its average rate exceeds the CIR and the available
bandwidth capacity accumulated in the first bucket if sufficient unused bandwidth
capacity is available in the second token bucket. Packets in a yellow flow are implicitly
marked with
medium-high
PLP and then passed through the interface.
A traffic flow is categorized red its average rate exceeds the CIR and the available
bandwidth capacity accumulated in the second bucket. Packets in a red flow are implicitly
marked with
high
PLP and then either passed through the interface or optionally discarded.
Copyright © 2016, Juniper Networks, Inc. 22
Traffic Policers Feature Guide for EX9200 Switches