Editing Traffic policing (communications) (section)

== Effects ==
The recipient of traffic that has been ''policed'' will observe [[packet loss]] distributed throughout periods when incoming traffic exceeded the contract. If the source does not limit its sending rate (for example, through a [[#Impact on Congestion-Controlled Sources|feedback mechanism]]), this will continue, and may appear to the recipient as if [[link errors]] or some other disruption is causing random packet loss. The received traffic, which has experienced policing en route, will typically comply with the contract, although [[jitter]] may be introduced by elements in the network downstream of the policer.

With reliable protocols, such as [[Transmission Control Protocol|TCP]] as opposed to [[User Datagram Protocol|UDP]], the dropped packets will not be acknowledged by the receiver, and therefore will be resent by the emitter, thus generating more traffic.

=== Impact on congestion-controlled sources ===
Sources with feedback-based [[congestion control]] mechanisms (for example [[Transmission Control Protocol|TCP]]) typically adapt rapidly to static policing, converging on a rate just below the policed sustained rate.{{Citation needed|date=November 2013}}

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Co-operative policing mechanisms, such as packet-based discard<ref>Design and applications of ATM LAN/WAN adapters. Bonjour, D.; De Hauteclocque, G.; Le Moal, J. ATM, 1998. ICATM-98., IEEE International Conference, 22-24 Jun 1998 Page(s):191 - 198 Digital Object Identifier 10.1109/ICATM.1998.688177</ref> facilitate more rapid convergence, higher stability and more efficient resource sharing.  As a result, it may be hard for endpoints to distinguish TCP traffic that has been merely policed from TCP traffic that has been [[traffic shaping|shaped]].

=== Impact in the case of ATM ===
Where [[cell relay|cell]]-level dropping is enforced (as opposed to that achieved through packet-based policing) the impact is particularly severe on longer packets. Since cells are typically much shorter than the maximum packet size, conventional policers discard cells which do not respect packet boundaries, and hence the total amount of traffic dropped will typically be distributed throughout a number of packets. Almost all known [[ATM Adaptation Layer 5#Convergence, segmentation, and reassembly|packet reassembly]] mechanisms will respond to a missing cell by dropping the packet entirely, and consequently a very large number of packet losses can result from moderately exceeding the policed contract.