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On a node in packet switching communication network, a network scheduler, also called packet scheduler, is an arbiter program that manages the sequence of network packets in the transmit and receive queues of the network interface controller, which is a circular data buffer. There are several network schedulers available for the different operating system kernels, that implement many of the existing network scheduling algorithms. The network scheduler logic decides, in a way similar to statistical multiplexers, which network packet to forward next from the buffer. The buffer works as a queuing system, storing the network packets temporarily until they are transmitted. The buffer space may be divided into different queues, with each of them holding the packets of one flow according to configured packet classification rules; for example, packets can be divided into flows by their source and destination IP addresses. Network scheduling algorithms and their associated settings determine how the network scheduler manages the buffer. Also, network schedulers are enabling accomplishment of the active queue management and traffic shaping. == Network scheduling algorithms == In the course of time several network scheduling algorithms (also called queueing discipline, qdisc or queueing algorithm) have been developed. Each of the scheduling algorithms used internally for these queuing disciplines provides specific reordering or dropping of network packets inside various transmit or receive buffers. Queuing disciplines are commonly used as attempts to compensate for various networking conditions, like reducing the latency for certain classes of network packets, and are generally used as part of the quality of service (QoS) measures. Examples of algorithms suitable for managing network traffic include: * AVQ (adaptive virtual queue)〔http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.108.4477&rep=rep1&type=pdf〕 * CBQ (class-based queueing) discipline * CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for unresponsive flows) is a variant of RED * CoDel (controlled delay) and fair/flow queue CoDel * Credit-based fair queuing * DRR (deficit round robin) and DWRR, implementation e.g. written by Patrick McHardy for the Linux kernel〔(【引用サイトリンク】title=DRR Linux kernel network scheduler module )〕 and published under the GNU General Public License. * GCRA (generic cell rate algorithm) * HFF (heavy-hitter filter)〔(【引用サイトリンク】title=Heavy-Hitter Filter qdisc )〕 * HFSC (hierarchical fair-service curve) * HTB (hierarchical token bucket)〔(【引用サイトリンク】title=HTB Linux kernel network scheduler module )〕 * QFQ (quick fair queueing)〔(【引用サイトリンク】title=QFQ Linux kernel network scheduler module )〕 * FQ (fair queuing) and WFQ (weighted fair queuing) * FIFO (first in, first out) * pkt_sched: fq: fair queue packet scheduler * NETEM network emulator〔(【引用サイトリンク】title=Network emulator Linux kernel network scheduler module )〕 * PIE (proportional integral controller enhanced)〔(【引用サイトリンク】title=Proportional Integral controller Enhanced (PIE) )〕 * RED (random early detection) as well as ARED (advanced random early detection, GRED (generalized random early detection), RRED (robust random early detection) and WRED (weighted random early detection) * RR (round-robin) and WRR (weighted round robin) * SFB (stochastic fair blue) as well as RSFB (resilient SFB) * SFQ (stochastic fairness queuing)〔(【引用サイトリンク】title=SFQ Linux kernel network scheduler module )〕 * TBF (token bucket filter)〔(【引用サイトリンク】title=TBF Linux kernel network scheduler module )〕 * TEQL (trivial link equalizer) Several of the above have been implemented as Linux kernel modules and are freely available. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「network scheduler」の詳細全文を読む スポンサード リンク
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