Editing Round-robin scheduling (section)

==Network packet scheduling==
{{Main|Network scheduler}}
In [[best-effort]] [[packet switching]] and other [[statistical multiplexing]], round-robin scheduling can be used as an alternative to [[first-come first-served]] queuing.

A multiplexer, switch, or router that provides round-robin scheduling has a separate queue for every data flow, where a data flow may be identified by its source and destination address. The algorithm allows every active data flow that has data packets in the queue to take turns in transferring packets on a shared channel in a periodically repeated order. The scheduling is [[Work-conserving scheduler|work-conserving]], meaning that if one flow is out of packets, the next data flow will take its place. Hence, the scheduling tries to prevent link resources from going unused.

Round-robin scheduling results in [[max-min fairness]] if the data packets are equally sized, since the data flow that has waited the longest time is given scheduling priority. It may not be desirable if the size of the data packets varies widely from one job to another. A user that produces large packets would be favored over other users. In that case [[fair queuing]] would be preferable.

If guaranteed or differentiated quality of service is offered, and not only best-effort communication, [[deficit round robin|deficit round-robin]] (DRR) scheduling, [[weighted round robin|weighted round-robin]] (WRR) scheduling, or [[weighted fair queuing]] (WFQ) may be considered.

In [[multiple access|multiple-access]] networks, where several terminals are connected to a shared physical medium, round-robin scheduling may be provided by [[token passing]] [[channel access]] schemes such as [[Token Ring]], or by [[polling (computer science)|polling]] or resource reservation from a central control station.

In a centralized wireless packet radio network, where many stations share one frequency channel, a scheduling algorithm in a central base station may reserve time slots for the mobile stations in a round-robin fashion and provide fairness. However, if [[link adaptation]] is used, it will take a much longer time to transmit a certain amount of data to "expensive" users than to others since the channel conditions differ. It would be more efficient to wait with the transmission until the channel conditions are improved, or at least to give scheduling priority to less expensive users. Round-robin scheduling does not utilize this. Higher throughput and [[system spectrum efficiency]] may be achieved by channel-dependent scheduling, for example a [[proportionally fair]] algorithm, or [[maximum throughput scheduling]]. Note that the latter is characterized by undesirable [[scheduling starvation]]. This type of scheduling is one of the very basic algorithms for Operating Systems in computers which can be implemented through a circular queue data structure.