Weighted fair queuing

Weighted fair queueing (WFQ) is a data packet scheduling algorithm used by network schedulers. WFQ is both a packet based implementation of the generalized processor sharing policy (GPS), and a natural generalization of fair queuing (FQ): whereas FQ shares the link's capacity in equal subparts, WFQ allows to specify, for each flow, which fraction of the capacity will be given.

Weighted fair queuing (WFQ) is also known as Packet-by-Packet GPS (PGPS or P-GPS) since it approximates generalized processor sharing "to within one packet transmission time, regardless of the arrival patterns."

Like other GPS-like scheduling algorithms, the choice of the weights is left to the network administrator.

By regulating the WFQ weights dynamically, WFQ can be utilized for controlling the quality of service, for example to achieve guaranteed data rate.

As presented for fair queueing, there is no unique definition on what is "fair".

Proportional fairness can be achieved by setting the weights to ${\displaystyle w_{i}=1/c_{i}}$, where ${\displaystyle c_{i}}$ is the cost per data bit of data flow ${\displaystyle i}$. For example in CDMA spread spectrum cellular networks, the cost may be the required energy (the interference level), and in dynamic channel allocation systems, the cost may be the number of nearby base station sites that can not use the same frequency channel, in view to avoid co-channel interference.

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