Editing Traffic policing (communications) (section)

== Process ==
RFC 2475 describes traffic policing elements like a ''meter'' and a ''dropper''.<ref>[http://tools.ietf.org/html/rfc2475#section-2.3.3.1 IETF RFC 2475] "An Architecture for Differentiated Services" section 2.3.3 - definitions of meter, dropper and marker</ref>  They may also optionally include a ''marker''. The meter measures the traffic and determines whether or not it exceeds the contract (for example by [[Generic cell rate algorithm|GCRA]]). Where it exceeds the contract, some policy determines if any given [[Protocol data unit|PDU]] is dropped, or if marking is implemented, if and how it is to be marked. Marking can comprise setting a congestion flag (such as [[Explicit Congestion Notification|ECN]] flag of [[Transmission Control Protocol|TCP]] or [[Cell Loss Priority|CLP]] bit of [[Asynchronous Transfer Mode|ATM]]) or setting a traffic aggregate indication (such as [[Differentiated Services]] Code Point of [[Internet Protocol|IP]]).

In simple implementations, traffic is classified into two categories, or "colors" : compliant (green) and in excess (red). RFC 2697 proposes a more precise classification, with three "colors".<ref>[http://tools.ietf.org/html/rfc2697 IETF RFC 2697] "A Single Rate Three Color Marker"</ref> In this document, the contract is described through three parameters: '''Committed Information Rate''' (CIR), '''Committed Burst Size''' (CBS), and '''Excess Burst Size''' (EBS). A packet is "green" if it doesn't exceed the CBS, "yellow" if it does exceed the CBS, but not the EBS, and "red" otherwise.

The "single-rate three-color marker" described by RFC 2697 allows for temporary bursts. The bursts are allowed when the line was under-used before they appeared. A more predictable algorithm is described in RFC 2698, which proposes a "double-rate three-color marker".<ref>[http://tools.ietf.org/html/rfc2698 IETF RFC 2698] "A Two Rate Three Color Marker"</ref> RFC 2698 defines a new parameter, the Peak Information Rate (PIR). RFC 2859 describes the "Time Sliding Window Three Colour Marker" which meters a traffic stream and marks packets based on measured throughput relative to two specified rates: Committed Target Rate (CTR) and Peak Target Rate (PTR).<ref>[http://tools.ietf.org/search/rfc2859 IETF RFC 2859] "A Time Sliding Window Three Color Marker"</ref>