Rochester Institute of Technology RIT Scholar Works Theses 7-2-2015 TCP – Random Early Detection (RED) mechanism for Congestion Control Asli Sungur [email protected] Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation Sungur, Asli, "TCP – Random Early Detection (RED) mechanism for Congestion Control" (2015). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. R.I.T TCP – Random Early Detection (RED) mechanism for Congestion Control by ASLI SUNGUR This thesis is presented as part of the Degree of Master of Science in Network and System Administration with emphasis in Networking Committee Members: Ali Raza Muhieddin Amer Nirmala Shenoy Information Science and Technologies Department, B. Thomas Golisano College of Computing & Information Sciences Rochester Institute of Technology Rochester, NY July 2, 2015 i Table of Contents Abstract ........................................................................................................................................................ iv Acknowledgement ........................................................................................................................................ v List of Figures .............................................................................................................................................. vi List of Formulas .......................................................................................................................................... vii Acronyms ..................................................................................................................................................... ix 1. Introduction ........................................................................................................................................... 1 1.1 TCP Sequence and Acknowledgement Numbering ...................................................................... 3 1.2 Problem Statement ........................................................................................................................ 5 2. Earlier congestion control techniques ................................................................................................. 10 2.1 Introduction ................................................................................................................................... 10 2.2 Tail Drop ..................................................................................................................................... 11 2.3 Random Drop .............................................................................................................................. 12 3. Random Early Detection ..................................................................................................................... 14 3.1 Introduction ................................................................................................................................. 14 3.2 RED Parameterization................................................................................................................. 14 3.2.1 Introduction ................................................................................................................................. 14 3.2.2 Wq parameterization .................................................................................................................... 16 3.2.3 Minth and Maxth parameterization ............................................................................................... 17 3.2.4 Average Queue Length ............................................................................................................... 18 3.3 RED Algorithm ........................................................................................................................... 19 3.4 Simulations ................................................................................................................................. 24 3.4.1 RED Simulations................................................................................................................. 24 3.4.2 RED and Tail Drop comparison .......................................................................................... 25 3.4.3 RED and Random Drop comparison................................................................................... 27 4. Improvements to RED ............................................................................................................................ 31 4.1 Introduction ................................................................................................................................... 31 4.2 Weighted RED .............................................................................................................................. 32 4.2.1 Cisco WRED Configuration ............................................................................................. 33 4.2.1.1 Enabling WRED .............................................................................................. 33 4.2.1.2 Configuring WRED in a Traffic Policy ........................................................... 34 4.2.1.3 DSCP Compliant WRED Configuration .......................................................... 35 4.2.2 Cisco WRED Implementations ........................................................................................... 36 ii 4.2.3 Juniper WRED Configuration ............................................................................................. 39 4.2.3.1 Enabling WRED .......................................................................................... 39 4.2.3.2 Configuring WRED in a Traffic Policy ....................................................... 40 4.2.4 Juniper WRED Implementations ........................................................................................ 43 4.3 Flow RED ...................................................................................................................................... 46 4.4 Adaptive RED ................................................................................................................................ 47 5. Conclusion .............................................................................................................................................. 50 6. Future work ............................................................................................................................................. 52 Glossary ...................................................................................................................................................... 53 References ................................................................................................................................................... 57 iii Abstract This thesis discusses the Random Early Detection (RED) algorithm, proposed by Sally Floyd, used for congestion avoidance in computer networking, how existing algorithms compare to this approach and the configuration and implementation of the Weighted Random Early Detection (WRED) variation. RED uses a probability approach in order to calculate the probability that a packet will be dropped before periods of high congestion, relative to the minimum and maximum queue threshold, average queue length, packet size and the number of packets since the last drop. The motivation for this thesis has been the high QoS provided to current delay-sensitive applications such as Voice-over-IP (VoIP) by the incorporation of congestion avoidance algorithms derived from the original RED design [45]. The WRED variation of RED is not directly invoked on the VoIP class because congestion avoidance mechanisms are not configured for voice queues. WRED is instead used to prioritize other traffic classes in order to avoid congestion to provide and guarantee high quality of service for voice traffic [43][44]. The most notable simulations performed for the RED algorithm in comparison to the Tail Drop (TD) and Random Drop (RD) algorithms have been detailed in order to show that RED is much more advantageous in terms of congestion control in a network. The WRED, Flow RED (FRED) and Adaptive RED (ARED) variations of the RED algorithm have been detailed with emphasis on WRED. Details of the concepts of forwarding classes, output queues, traffic policies, traffic classes, class maps, schedulers, scheduler maps, and DSCP classification shows that the WRED feature is easily configurable on tier-1 vendor routers. iv Acknowledgement I would like to express my gratitude to Dr. Ali Raza for his scholarly advice, valuable time and encouragement. Dr. Ali Raza’s vast knowledge in networking has helped me achieve a clear picture of concepts that were vital in my understanding of the complex algorithms detailed in this paper. I thank him whole-heartedly. Finally, I would like to thank my parents for their love and supporting me on my journey towards the completion of my degree. v List of Figures Figure 1: Data Transmission between two computers Figure 2: Slow-Start algorithm Figure 3: RED algorithm diagram Figure 4: RED simulation network Figure 5: RED and Tail Drop comparison simulation network Figure 6: Tail Drop delay time Figure 7: RED delay time Figure 8: RED and Random Drop comparison