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Single-Rate Three-Color Policer Overview

 

A single-rate three-color policer defines a bandwidth limit and a maximum burst size for guaranteed traffic and a second burst size for peak traffic. A single-rate three-color policer is most useful when a service is structured according to packet length and not peak arrival rate.

Single-rate three-color policing meters a traffic stream based on the following configured traffic criteria:

  • Committed information rate (CIR)—Bandwidth limit for guaranteed traffic.

  • Committed burst size (CBS)—Maximum packet size permitted for bursts of data that exceed the CIR.

  • Excess burst size (EBS)—Maximum packet size permitted for peak traffic.

Single-rate tricolor marking (single-rate TCM) classifies traffic as belonging to one of three color categories and performs congestion-control actions on the packets based on the color marking:

  • Green—Traffic that conforms to either the bandwidth limit or the burst size for guaranteed traffic (CIR or CBS). For a green traffic flow, single-rate  marks the packets with an implicit loss priority of low and transmits the packets.

  • Yellow—Traffic that exceeds both the bandwidth limit and the burst size for guaranteed traffic (CIR and CBS) but not the burst size for peak traffic (EBS). For a yellow traffic flow, single-rate marks the packets with an implicit loss priority of medium-high and transmits the packets.

  • Red—Traffic that exceeds the burst size for peak traffic (EBS), single-rate  marks packets with an implicit loss priority of high and, optionally, discards the packets.

If congestion occurs downstream, the packets with higher loss priority are more likely to be discarded.