Round - robin scheduling - wikipedia Round - robin scheduling This article is about scheduling in computing. For other uses, see Round - robin ( disambiguation ). This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( April 2015 ) A round - robin example with quantum = 3. Round - robin ( RR ) is one of the algorithms employed by process and network schedulers in computing. As the term is generally used, time slices ( also known as time quanta ) are assigned to each process in equal portions and in circular order, handling all processes without priority ( also known as cyclic executive ). Round - robin scheduling is simple, easy to implement, and starvation - free. Round - robin scheduling can also be applied to other scheduling problems, such as data packet scheduling in computer networks. It is an operating system concept. The name of the algorithm comes from the round - robin principle known from other fields, where each person takes an equal share of something in turn. Contents 1 Process scheduling 2 Network packet scheduling 3 See also 4 References Process scheduling Main article : Process scheduler To schedule processes fairly, a round - robin scheduler generally employs time - sharing, giving each job a time slot or quantum ( its allowance of CPU time ), and interrupting the job if it is not completed by then. The job is resumed next time a time slot is assigned to that process. If the process terminates or changes its state to waiting during its attributed time quantum, the scheduler selects the first process in the ready queue to execute. In the absence of time - sharing, or if the quanta were large relative to the sizes of the jobs, a process that produced large jobs would be favoured over other processes. Round - robin algorithm is a pre-emptive algorithm as the scheduler forces the process out of the CPU once the time quota expires. For example, if the time slot is 100 milliseconds, and job1 takes a total time of 250 ms to complete, the round - robin scheduler will suspend the job after 100 ms and give other jobs their time on the CPU. Once the other jobs have had their equal share ( 100 ms each ), job1 will get another allocation of CPU time and the cycle will repeat. This process continues until the job finishes and needs no more time on the CPU. Job1 = Total time to complete 250 ms ( quantum 100 ms ). First allocation = 100 ms. Second allocation = 100 ms. Third allocation = 100 ms Total CPU time of job1 = 250 ms Consider the following table with the arrival time and execute time of the process with the quantum time of 100ms to understand the round - robin scheduling : Process name Arrival time Execute time P0 0 250 P1 50 170 P2 130 75 P3 190 100 P4 210 130 P5 350 50 Another approach is to divide all processes into an equal number of timing quanta such that the quantum size is proportional to the size of the process. Hence, all processes end at the same time. Network packet scheduling Main article : 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 lets 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, 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 ( DRR ) scheduling, weighted round - robin ( WRR ) scheduling, or weighted fair queuing ( WFQ ) may be considered. In 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 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 circular queue data structure. See also Weighted round robin Deficit round robin Multilevel queue References Jump up ^ Arpaci - Dusseau, Remzi H. ; Arpaci - Dusseau, Andrea C. ( 2014 ), Operating Systems : Three Easy Pieces ( Chapter : Scheduling Introduction ) ( PDF ), Arpaci - Dusseau Books Jump up ^ Guowang Miao, Jens Zander, Ki Won Sung, and Ben Slimane, Fundamentals of Mobile Data Networks, Cambridge University Press, ISBN 1107143217, 2016. Jump up ^ Stallings, William ( 2015 ). Operating Systems : Internals and Design Principles. Pearson. p. 409. ISBN 978 - 0 - 13 - 380591 - 8. Jump up ^ Silberschatz, Abraham ; Galvin, Peter B. ; Gagne, Greg ( 2010 ). `` Process Scheduling ''. Operating System Concepts ( 8th ed. ). John_Wiley_&_Sons ( Asia ). p. 194. ISBN 978 - 0 - 470 - 23399 - 3. 5.3. 4 Round Robin Scheduling Queueing theory Single queueing nodes D / M / 1 queue M / D / 1 queue M / D / c queue M / M / 1 queue Burke 's theorem M / M / c queue M / M / ∞ queue M / G / 1 queue Pollaczek -- Khinchine formula Matrix analytic method M / G / k queue G / M / 1 queue G / G / 1 queue Kingman 's formula Lindley equation Fork -- join queue Bulk queue Arrival processes Poisson process Markovian arrival process Rational arrival process Queueing networks Jackson network Traffic equations Gordon -- Newell theorem Mean value analysis Buzen 's algorithm Kelly network G - network BCMP network Service policies FIFO LIFO Processor sharing Round - robin Shortest job first Shortest remaining time Key concepts Continuous - time Markov chain Kendall 's notation Little 's law Product - form solution Balance equation Quasireversibility Flow - equivalent server method Arrival theorem Decomposition method Beneš method Limit theorems Fluid limit Mean field theory Heavy traffic approximation Reflected Brownian motion Extensions Fluid queue Layered queueing network Polling system Adversarial queueing network Loss network Retrial queue Information systems Data buffer Erlang ( unit ) Erlang distribution Flow control ( data ) Message queue Network congestion Network scheduler Pipeline ( software ) Quality of service Scheduling ( computing ) Teletraffic engineering Retrieved from `` https://en.wikipedia.org/w/index.php?title=Round-robin_scheduling&oldid=809102453 '' Categories : Processor scheduling algorithms Network scheduling algorithms Hidden categories : Articles needing additional references from April 2015 All articles needing additional references Talk Contents About Wikipedia Čeština Deutsch Eesti Ελληνικά Español فارسی Français 한국어 Italiano Magyar Nederlands 日本 語 Norsk Polski Português Русский Slovenščina Svenska Українська 中文 Edit links This page was last edited on 7 November 2017, at 03 : 53. 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Question: protocol that is used to transmit data without any schedule time is
Answer: Round-robin