Editing Priority queue (section)

=== Bandwidth management ===

Priority queuing can be used to manage limited resources such as [[Bandwidth (computing)|bandwidth]] on a transmission line from a [[computer network|network]] [[router (computing)|router]]. In the event of outgoing [[traffic]] queuing due to insufficient bandwidth, all other queues can be halted to send the traffic from the highest priority queue upon arrival. This ensures that the prioritized traffic (such as real-time traffic, e.g. an [[Real-time Transport Protocol|RTP]] stream of a [[Voice over Internet Protocol|VoIP]] connection) is forwarded with the least delay and the least likelihood of being rejected due to a queue reaching its maximum capacity. All other traffic can be handled when the highest priority queue is empty. Another approach used is to send disproportionately more traffic from higher priority queues.

Many modern protocols for [[local area network]]s also include the concept of priority queues at the [[media access control]] (MAC) sub-layer to ensure that high-priority applications (such as [[VoIP]] or [[IPTV]]) experience lower latency than other applications which can be served with [[best-effort service]]. Examples include [[IEEE 802.11e]] (an amendment to [[IEEE 802.11]] which provides [[quality of service]]) and [[ITU-T]] [[G.hn]] (a standard for high-speed [[local area network]] using existing home wiring ([[Power line communication|power lines]], phone lines and [[Ethernet over coax|coaxial cables]]).

Usually a limitation (policer) is set to limit the bandwidth that traffic from the highest priority queue can take, in order to prevent high priority packets from choking off all other traffic. This limit is usually never reached due to high level control instances such as the [[Cisco Systems, Inc.|Cisco]] [[Callmanager]], which can be programmed to inhibit calls which would exceed the programmed bandwidth limit.
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Priority queues exist on ISO-layer 2 (which is Ethernet or WAN interfaces such as T1 / E1) and are filled by entry-criterions such as [[Diffserv]] Codepoints or IP-Precedence. Network equipment usually can be programmed to pick up priority packets by the layer 4 info (IP protocol and port) or the new one by a mechanism called [[NBAR]].
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