Scheduling for Fairness: Fair Queueing and CSFQ
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15-744: Computer Networking Fair Queuing Overview Example
Fair Queuing • Fair Queuing • Core-stateless Fair queuing 15-744: Computer Networking • Assigned reading • Analysis and Simulation of a Fair Queueing Algorithm, Internetworking: Research and Experience L-7 Fair Queuing • Congestion Control for High Bandwidth-Delay Product Networks (XTP - 2 sections) 2 Overview Example • 10Gb/s linecard • TCP and queues • Requires 300Mbytes of buffering. • Queuing disciplines • Read and write 40 byte packet every 32ns. •RED • Memory technologies • DRAM: require 4 devices, but too slow. • Fair-queuing • SRAM: require 80 devices, 1kW, $2000. • Core-stateless FQ • Problem gets harder at 40Gb/s • Hence RLDRAM, FCRAM, etc. •XCP 3 4 1 Rule-of-thumb If flows are synchronized • Rule-of-thumb makes sense for one flow Wmax • Typical backbone link has > 20,000 flows • Does the rule-of-thumb still hold? Wmax 2 Wmax Wmax 2 t • Aggregate window has same dynamics • Therefore buffer occupancy has same dynamics • Rule-of-thumb still holds. 5 6 If flows are not synchronized Central Limit Theorem W B • CLT tells us that the more variables (Congestion 0 Windows of Flows) we have, the narrower the Gaussian (Fluctuation of sum of windows) • Width of Gaussian decreases with 1 n 1 • Buffer size should also decreases with n Bn1 2T C Buffer Size Probability B Distribution n n 7 8 2 Required buffer size Overview • TCP and queues • Queuing disciplines •RED 2TC n • Fair-queuing • Core-stateless FQ Simulation •XCP 9 10 Queuing Disciplines Packet Drop Dimensions • Each router must implement some queuing discipline Aggregation Per-connection -
15-744: Computer Networking Fair Queuing Overview Example
Fair Queuing • Fair Queuing • Core-stateless Fair queuing 15-744: Computer Networking • Assigned reading • [DKS90] Analysis and Simulation of a Fair Queueing Algorithm, Internetworking: Research and Experience L-5 Fair Queuing • [SSZ98] Core-Stateless Fair Queueing: Achieving Approximately Fair Allocations in High Speed Networks 2 Overview Example • 10Gb/s linecard • TCP and queues • Requires 300Mbytes of buffering. • Queuing disciplines • Read and write 40 byte packet every 32ns. • RED • Memory technologies • DRAM: require 4 devices, but too slow. • Fair-queuing • SRAM: require 80 devices, 1kW, $2000. • Core-stateless FQ • Problem gets harder at 40Gb/s • Hence RLDRAM, FCRAM, etc. • XCP 3 4 1 Rule-of-thumb If flows are synchronized • Rule-of-thumb makes sense for one flow • Typical backbone link has > 20,000 flows • Does the rule-of-thumb still hold? t • Aggregate window has same dynamics • Therefore buffer occupancy has same dynamics • Rule-of-thumb still holds. 5 6 If flows are not synchronized Central Limit Theorem B • CLT tells us that the more variables (Congestion 0 Windows of Flows) we have, the narrower the Gaussian (Fluctuation of sum of windows) • Width of Gaussian decreases with • Buffer size should also decreases with Buffer Size Probability Distribution 7 8 2 Required buffer size Overview • TCP and queues • Queuing disciplines • RED • Fair-queuing • Core-stateless FQ Simulation • XCP 9 10 Queuing Disciplines Packet Drop Dimensions • Each router must implement some queuing discipline Aggregation Per-connection state Single -
Queue Scheduling Disciplines
White Paper Supporting Differentiated Service Classes: Queue Scheduling Disciplines Chuck Semeria Marketing Engineer Juniper Networks, Inc. 1194 North Mathilda Avenue Sunnyvale, CA 94089 USA 408 745 2000 or 888 JUNIPER www.juniper.net Part Number:: 200020-001 12/01 Contents Executive Summary . 4 Perspective . 4 First-in, First-out (FIFO) Queuing . 5 FIFO Benefits and Limitations . 6 FIFO Implementations and Applications . 6 Priority Queuing (PQ) . 6 PQ Benefits and Limitations . 7 PQ Implementations and Applications . 8 Fair Queuing (FQ) . 9 FQ Benefits and Limitations . 9 FQ Implementations and Applications . 10 Weighted Fair Queuing (WFQ) . 11 WFQ Algorithm . 11 WFQ Benefits and Limitations . 13 Enhancements to WFQ . 14 WFQ Implementations and Applications . 14 Weighted Round Robin (WRR) or Class-based Queuing (CBQ) . 15 WRR Queuing Algorithm . 15 WRR Queuing Benefits and Limitations . 16 WRR Implementations and Applications . 18 Deficit Weighted Round Robin (DWRR) . 18 DWRR Algorithm . 18 DWRR Pseudo Code . 19 DWRR Example . 20 DWRR Benefits and Limitations . 24 DWRR Implementations and Applications . 25 Conclusion . 25 References . 26 Textbooks . 26 Technical Papers . 26 Seminars . 26 Web Sites . 27 Copyright © 2001, Juniper Networks, Inc. List of Figures Figure 1: First-in, First-out (FIFO) Queuing . 5 Figure 2: Priority Queuing . 7 Figure 3: Fair Queuing (FQ) . 9 Figure 4: Class-based Fair Queuing . 11 Figure 5: A Weighted Bit-by-bit Round-robin Scheduler with a Packet Reassembler . 12 Figure 6: Weighted Fair Queuing (WFQ)—Service According to Packet Finish Time . 13 Figure 7: Weighted Round Robin (WRR) Queuing . 15 Figure 8: WRR Queuing Is Fair with Fixed-length Packets . 17 Figure 9: WRR Queuing is Unfair with Variable-length Packets . -
Enhanced Core Stateless Fair Queuing with Multiple Queue Priority Scheduler
The International Arab Journal of Information Technology, Vol. 11, No. 2, March 2014 159 Enhanced Core Stateless Fair Queuing with Multiple Queue Priority Scheduler Nandhini Sivasubramaniam 1 and Palaniammal Senniappan 2 1Department of Computer Science, Garden City College of Science and Management Studies, India 2Department of Science and Humanities, VLB Janakiammal College of Engineering and Technology, India Abstract: The Core Stateless Fair Queuing (CSFQ) is a distributed approach of Fair Queuing (FQ). The limitations include its inability to estimate fairness during large traffic flows, which are short and bursty (VoIP or video), and also it utilizes the single FIFO queue at the core router. For improving the fairness and efficiency, we propose an Enhanced Core Stateless Fair Queuing (ECSFQ) with multiple queue priority scheduler. Initially priority scheduler is applied to the flows entering the ingress edge router. If it is real time flow i.e., VoIP or video flow, then the packets are given higher priority else lower priority. In core router, for higher priority flows the Multiple Queue Fair Queuing (MQFQ) is applied that allows a flow to utilize multiple queues to transmit the packets. In case of lower priority, the normal max-min fairness criterion of CSFQ is applied to perform probabilistic packet dropping. By simulation results, we show that this technique improves the throughput of real time flows by reducing the packet loss and delay. Keywords: CSFQ, quality of service, MQFQ, priority scheduler. Received November 21, 2011; accepted July 29, 2012; published online January 29, 2013 1. Introduction 1.2. Fair Queuing Techniques 1.1. Queuing Algorithms in Networking Queuing in networking includes techniques like priority queuing [7, 11, 13], Fair Queuing (FQ) [2, 10, Queueing Theory is a branch of applied probability 19] and Round Robin Queuing [12, 15, 16]. -
Per-Flow Fairness in the Datacenter Network Yixi Gong, James W
1 Per-Flow Fairness in the Datacenter Network YiXi Gong, James W. Roberts, Dario Rossi Telecom ParisTech Abstract—Datacenter network (DCN) design has been ac- produced by gaming applications [1], instant voice transla- tively researched for over a decade. Solutions proposed range tion [29] and augmented reality services, for example. The from end-to-end transport protocol redesign to more intricate, exact flow mix will also be highly variable in time, depending monolithic and cross-layer architectures. Despite this intense activity, to date we remark the absence of DCN proposals based both on the degree to which applications rely on offloading to on simple fair scheduling strategies. In this paper, we evaluate the Cloud and on the accessibility of the Cloud that varies due the effectiveness of FQ-CoDel in the DCN environment. Our to device capabilities, battery life, connectivity opportunity, results show, (i) that average throughput is greater than that etc. [9]. attained with DCN tailored protocols like DCTCP, and (ii) the As DCN resources are increasingly shared among multiple completion time of short flows is close to that of state-of-art DCN proposals like pFabric. Good enough performance and stakeholders, we must question the appropriateness of some striking simplicity make FQ-CoDel a serious contender in the frequently made assumptions. How can one rely on all end- DCN arena. systems implementing a common, tailor-made transport pro- tocol like DCTCP [6] when end-systems are virtual machines under tenant control? How can one rely on applications I. INTRODUCTION truthfully indicating the size of their flows to enable shortest In the last decade, datacenter networks (DCNs) have flow first scheduling as in pFabric [8] when a tenant can gain increasingly been built with relatively inexpensive off-the- better throughput by simply slicing a long flow into many shelf devices. -
An Extension of the Codel Algorithm
Proceedings of the International MultiConference of Engineers and Computer Scientists 2015 Vol II, IMECS 2015, March 18 - 20, 2015, Hong Kong Hard Limit CoDel: An Extension of the CoDel Algorithm Fengyu Gao, Hongyan Qian, and Xiaoling Yang Abstract—The CoDel algorithm has been a significant ad- II. BACKGROUND INFORMATION vance in the field of AQM. However, it does not provide bounded delay. Rather than allowing bursts of traffic, we argue that a Nowadays the Internet is suffering from high latency and hard limit is necessary especially at the edge of the Internet jitter caused by unprotected large buffers. The “persistently where a single flow can congest a link. Thus in this paper we full buffer problem”, recently exposed as “bufferbloat” [1], proposed an extension of the CoDel algorithm called “hard [2], has been observed for decades, but is still with us. limit CoDel”, which is fairly simple but effective. Instead of number of packets, this extension uses the packet sojourn time When recognized the problem, Van Jacobson and Sally as the metric of limit. Simulation experiments showed that the Floyd developed a simple and effective algorithm called RED maximum delay and jitter have been well controlled with an (Random Early Detection) in 1993 [3]. In 1998, the Internet acceptable loss on throughput. Its performance is especially Research Task Force urged the deployment of active queue excellent with changing link rates. management in the Internet [4], specially recommending Index Terms—bufferbloat, CoDel, AQM. RED. However, this algorithm has never been widely deployed I. INTRODUCTION because of implementation difficulties. The performance of RED depends heavily on the appropriate setting of at least The CoDel algorithm proposed by Kathleen Nichols and four parameters: Van Jacobson in 2012 has been a great innovation in AQM. -
University of Bradford Ethesis
Performance Modelling and Analysis of Weighted Fair Queueing for Scheduling in Communication Networks. An investigation into the Development of New Scheduling Algorithms for Weighted Fair Queueing System with Finite Buffer. Item Type Thesis Authors Alsawaai, Amina S.M. Rights <a rel="license" href="http://creativecommons.org/licenses/ by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by- nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http:// creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. Download date 26/09/2021 15:01:09 Link to Item http://hdl.handle.net/10454/4877 University of Bradford eThesis This thesis is hosted in Bradford Scholars – The University of Bradford Open Access repository. Visit the repository for full metadata or to contact the repository team © University of Bradford. This work is licenced for reuse under a Creative Commons Licence. Performance Modelling and Analysis of Weighted Fair Queueing for Scheduling in Communication Networks An investigation into the Development of New Scheduling Algorithms for Weighted Fair Queueing System with Finite Buffer Amina Said Mohammed Alsawaai Submitted for the Degree of Doctor of Philosophy Department of Computing School of Computing, Informatics and Media University of Bradford 2010 Abstract Analytical modelling and characterization of Weighted Fair Queueing (WFQ) have re- cently received considerable attention by several researches since WFQ offers the min- imum delay and optimal fairness guarantee. However, all previous work on WFQ has focused on developing approximations of the scheduler with an infinite buffer because of supposed scalability problems in the WFQ computation. -
K04-2: Distributed Weighted Fair Queuing in 802.11 Wireless
Distributed Weighted Fair Queuing in 802.11 Wireless LAN Albert Banchs, Xavier P´erez NEC Europe Ltd., Network Laboratories Heidelberg, Germany Abstract— With Weighted Fair Queuing, the link’s bandwidth Specifically, the station computes a random value in the is distributed among competing flows proportionally to their range of 0 to the so-called Contention Window (CW). A backoff weights. In this paper we propose an extension of the DCF func- Ì = time interval is computed usingthis random value: back Óf f tion of IEEE 802.11 to provide weighted fair queuing in Wireless Ì Ê aÒd´¼;Cϵ £ Ì ×ÐÓØ LAN. Simulation results show that the proposed scheme is able ×ÐÓØ ,where is the slot time. This backoff to provide the desired bandwidth distribution independent of the interval is then used to initialize the backoff timer. This timer flows aggressiveness and their willingness to transmit. Backwards is decreased only when the medium is idle. The timer is frozen compatibility is provided such that legacy IEEE 802.11 terminals when another station is detected as transmitting. Each time the receive a bandwidth corresponding to the default weight. medium becomes idle for a period longer than DIFS, the back- Index Terms— Wireless LAN, IEEE 802.11, MAC, Weighted off timer is periodically decremented, once every slot-time. Fair Queuing, Bandwidth Allocation As soon as the backoff timer expires, the station accesses the medium. A collision occurs when two or more stations start I. INTRODUCTION transmission simultaneously in the same slot. An acknowledg- ment is used to notify the sendingstations that the transmitted Much research has been performed on ”weighted fair queu- frame has been successfully received. -
The So-Called Qos Is for Different Needs of Various Network Applications, and Provides Different Quality of Service, Such As
The so-called QoS is for different needs of various network applications, and provides different quality of service, such as providing dedicated bandwidth, reducing packet loss rate, reducing packet transmission delay and delay jitter. That is to say, in the case that the bandwidth is not sufficient, the contradiction between the bandwidth occupied by various service flows is balanced. The switch classifies the data streams in the ingress phase, and then maps different types of data streams to different priority queues in the export phase. Finally, the scheduling mode determines the manner in which packets of different priority queues are forwarded, thereby implementing QoS features. QoS working principle 1.Message classification: objects are identified according to certain matching rules. 2.Mapping: Users can map packets entering the switch to different priority queues according to the priority mode. The switch provides two priority modes: 802.1P priority and DSCP priority. 3.Queue scheduling: When the network is congested, it must solve the problem that multiple data streams compete for resources at the same time, usually by queue scheduling. The company's switches provide a total of five scheduling modes (supporting several of them depending on the switch chip), respectively SP(Strict Priority),RR(Round-Robin)WRR(Weighted Round-Robin)DRR(Deficit Round-Robin),WFQ(Weighted Fair Queuing). 1、Basic concept of QoS queue scheduling (1)802.1P priority 802.1Q Frame format As shown in the figure, each 802.1Q Tag has a Pri field, which consists of three bits, ranging from 0 to 7. The 802.1P priority is based on the Pri field value to determine the priority of the data frame level. -
Qos in IEEE 802.11-Based Wireless Networks: a Contemporary Survey Aqsa Malik, Junaid Qadir, Basharat Ahmad, Kok-Lim Alvin Yau, Ubaid Ullah
1 QoS in IEEE 802.11-based Wireless Networks: A Contemporary Survey Aqsa Malik, Junaid Qadir, Basharat Ahmad, Kok-Lim Alvin Yau, Ubaid Ullah. Abstract—Apart from mobile cellular networks, IEEE 802.11- requirements at a lower cost. In IEEE 802.11 WLANs, the based wireless local area networks (WLANs) represent the error and interference prone nature of wireless medium—due most widely deployed wireless networking technology. With the to fading and multipath effects [2]—makes QoS provisioning migration of critical applications onto data networks, and the emergence of multimedia applications such as digital audio/video even more challenging. The combination of best-effort routing, and multimedia games, the success of IEEE 802.11 depends datagram routing, and an unreliable wireless medium, makes critically on its ability to provide quality of service (QoS). A lot the task of QoS provisioning in IEEE 802.11 WLANs very of research has focused on equipping IEEE 802.11 WLANs with challenging. features to support QoS. In this survey, we provide an overview of In this survey, we provide a focused overview of work these techniques. We discuss the QoS features incorporated by the IEEE 802.11 standard at both physical (PHY) and media access done to ensure QoS in the IEEE 802.11 standard. We have control (MAC) layers, as well as other higher-layer proposals. We the following three goals: (i) to provide a self-contained also focus on how the new architectural developments of software- introduction to the QoS features embedded in the IEEE defined networking (SDN) and cloud networking can be used to 802.11 standard; (ii) to provide a layer-wise description and facilitate QoS provisioning in IEEE 802.11-based networks. -
CS640: Introduction to Computer Networks Queuing Disciplines Typical Internet Queuing
11/29/2007 CS640: Introduction to Computer Networks Aditya Akella Lecture 20 - Queuing and Basics of QoS Queuing Disciplines • Each router must implement some queuing discipline – Scheduling discipline – Drop policy • Queuing allocates both bandwidth and buffer space: – Bandwidth: which packet to serve (transmit) next – Buffer space: which packet to drop next (when required) • Queuing also affects latency 2 Typical Internet Queuing • FIFO + drop-tail – Simplest choice – Used widely in the Internet – FIFO: scheduling discipline – Drop-tail: drop policy • FIFO (first-in-first-out) – Implies single class of traffic, no priority • Drop-tail – Arriving packets get dropped when queue is full regardless of flow or importance 3 1 11/29/2007 FIFO + Drop-tail Problems • Lock-out problem – Allows a few flows to monopolize the queue space – Send more, get more No implicit policing • Full queues – TCP detects congestion from loss – Forces network to have long standing queues in steady-state – Queueing delays – bad for time sensitive traffic – Synchronization: end hosts react to same events • Full queue empty Full empty… • Poor support for bursty traffic 4 Lock-out Problem • Priority queueing can solve some problems – Starvation – Determining priorities is hard • Simpler techniques: Random drop – Packet arriving when queue is full causes some random packet to be dropped • Drop front – On full queue, drop packet at head of queue • Random drop and drop front solve the lock- out problem but not the full-queues problem 5 Random Early Detection (RED) -
Congestion Control Outline
Congestion Control and Resource Allocation Lecture material taken from “Computer Networks A Systems Approach”, Third Edition,Peterson and Davie, Morgan Kaufmann, 2007. Congestion Control Outline • Congestion Control • Flows • CC Taxonomy • Evaluation Criteria • Introduction to Queueing – FIFO (FCFS drop tail) – Priority – FQ (Fair Queueing) – WFQ (Weighted Fair Queueing) Computer Networks Congestion Control 2 Definitions • Flow control:: keep a fast sender from overrunning a slow receiver. • Congestion control:: the efforts made by network nodes to prevent or respond to overload conditions. Congestion control is intended to keep a fast sender from sending data into the network due to a lack of resources in the network {e.g., available link capacity, router buffers}. Computer Networks Congestion Control 3 Congestion Control • Congestion control is concerned with the bottleneck routers in a packet switched network. • Congestion control can be distinguished from routing in that sometimes there is no way to ‘route around’ a congested router. Computer Networks Congestion Control 4 Congestion 3 6 1 4 8 2 5 7 Copyright ©2000 The McGraw Hill Leon-Garcia & Widjaja: Communication Copyright ©2000 CompaniesThe McGraw Hill Companies LeonLeon-LeonGarcia-Garcia-Garcia & &Networks Widjaja: &Widjaja: Widjaja: Communication Communication Communication Networks Figure 7.50b NetworksNetworks Computer Networks Congestion Control 5 Source 1 10-Mbps Ethernet Router Destination 1.5-Mbps T1 link Source 100-Mbps FDDI 2 Figure 6.1 Congestion in a packet- switched network Computer Networks Congestion Control 6 Flows • flow :: a sequence of packets sent between a source/destination pair and following the same route through the network. • Connectionless flows within the TCP/IP model:: The connection-oriented abstraction, TCP, is implemented at the transport layer while IP provides a connectionless datagram delivery service.