The RED Algorithm – Averaged Queue Weight Modeling for Non Linear Traffic
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MEE09:78 The RED Algorithm – Averaged Queue Weight Modeling for Non Linear Traffic Sridhar Madipelli David Raj Gillella Sudhakar Devaraya This thesis is presented as part of the Degree of Master of Science in Electrical Engineering with Emphasis in Telecommunication Blekinge Institute of Technology November 2009 Master of Science Program in Electrical Engineering School of Computing Blekinge Institute of Technology Advisor: Dr. Doru Constantinescu Examiner: Dr. Doru Constantinescu i ii Abstract This thesis presents an approach in developing a congestion avoidance algorithm in computer networks for router-based communication. In internet communications, the requests generated are transferred through network nodes called routers which routes information, from one node to another, depending upon the request made. As the traffic load increases in the communication links, the routers must be designed to provide fair traffic flows, from a source to a destination, for all network nodes. During heavy traffic conditions the routers may get congested and the traffic flow through such a router degrades rapidly resulting in heavy packet dropping. Furthermore, this fact may also lead to a complete traffic collapse. To achieve fair transportation through such routers, the routers must be designed and provisioned with advanced congestion avoidance algorithms in order to achieve good performance. Congestion avoidance algorithms were used in the past, e.g. Active Queue Management (AQM), or the Drop Tail (DT) algorithm. To reduce the congestion effect, a new congestion avoidance algorithm named Random Early Detection (RED) was suggested. In RED, the calculation of packet dropping probabilities uses a queue weight factor. When compared to the previous RED approach, a fixed value is assigned leading to constant congestion reduction and if the network is varied randomly this fixed value may result in over congestion. To avoid this, an average queue weight parameter is developed. This algorithm is evaluated on router architecture for its practical feasibility and this mechanism is evaluated for various quality metrics such as throughput, network overhead, congestion level, transportation delay, etc. Due to its high cost in implementation on the network side, the proposed RED algorithm is evaluated through simulations and the obtained results are used to illustrate the performance of RED-DT by using MATLAB version 7.4. iii iv Acknowledgement We are greatly indebted to our supervisor Dr. Doru Constantinescu at, School of Computing, Blekinge Institute of Technology, who have guided our thesis work with scholarly advice, meticulous care and spared us valuable time. Without his moral support, guidance and encouragement this task would have been unachievable. We express our heartfelt gratitude to him. We would like to thank Mr. Anders Nelsson, the project coordinator, who spared time and evinced for our thesis work to be in process. We thank him whole heartedly. We want also to thank Mr. Mikael Åsman, program manager and Mrs. Lena Magnusson, program coordinator for their continuous encouragement, help and motivation in completion of our degree. We are thankful for their scholarly advice and for being source of continuous encouragement throughout the program. We would also like to thank the department, staff and teachers who contributed with their time and effort in completion of our program. We extend our sincere thanks to our family members and all our friends who helped us in completion of this project. v TABLE OF CONTENTS Abstract ............................................................................................................................... iii Acknowledgement ................................................................................................................ v List of Figures .................................................................................................................... viii List of Tables ....................................................................................................................... ix Acronyms ............................................................................................................................. x 1. Introduction ....................................................................................................................... 1 1.1 Brief Introduction ........................................................................................................ 1 1.1.1 Origin .................................................................................................................... 2 1.1.2 Motivation ............................................................................................................. 2 1.2 Aim of the Thesis ........................................................................................................ 3 1.3 Problem Statement ....................................................................................................... 3 1.4 Scope of the Thesis ...................................................................................................... 6 2.1Existing Systems........................................................................................................... 7 2.1.1 Drop Tail Router ................................................................................................... 7 2.1.2 Source Quench ...................................................................................................... 7 2.1.3 First in First Out .................................................................................................... 8 2.1.4 Random Drop Router ............................................................................................ 8 2.1.5 Congestion Indication ............................................................................................ 9 2.1.6 Random Early Drop............................................................................................... 9 2.2 Proposed System........................................................................................................ 10 2.3 RED Analysis ............................................................................................................ 12 2.4 RED Functionality ..................................................................................................... 13 2.5 RED‟s impact on traffic flow ..................................................................................... 13 2.6 Comparison between the RED and DT ....................................................................... 14 3. Simulation ....................................................................................................................... 15 3.1 Output: ...................................................................................................................... 15 vi 4. Design and Implementation ............................................................................................. 24 4.1 Flow of the Project..................................................................................................... 25 4.2 System Design ........................................................................................................... 26 4.2.1 Functional Description ........................................................................................ 28 4.3 Input Interface ........................................................................................................... 30 4.4 Analysis of Complete System .................................................................................... 37 4.5 RED Algorithm ......................................................................................................... 38 4.5.1RED Final Drop Probability ................................................................................. 40 4.5.2 Average Queue Length ........................................................................................ 40 4.5.3 RED Parameter Settings ...................................................................................... 42 4.6 Evaluation of RED Parameters ................................................................................... 43 5. Applications and Limitations ........................................................................................... 45 5.1 Applications............................................................................................................... 45 5.2 Limitations ................................................................................................................ 45 6. Conclusion ...................................................................................................................... 47 7. Future work ..................................................................................................................... 48 Appendix A ..................................................................................................................... 49 Appendix B ..................................................................................................................... 50 Bibliography .................................................................................................................... 54 vii List of Figures Figure1. 1: Network congestion Figure1. 2: Blocking probability using DT Figure2. 1: Drop Tail Router Figure2. 2: Random Drop Router Figure2. 3: Network with CE Figure2. 4: Random Early Drop Router Figure2. 5: Network with RED gateway Figure2.