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An Application of Active Congestion Control In An Application of Active Congestion Control in Abdollah Aghassi A thesis submitted in conformity with the requirernents for the degree of Master of Applied Science Graduate Department of Electrical and Computer Engineering University of Toronto O Copyright by Abdollah Aghassi 2000 National Library Bibliothéque nationale I*I of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington Ottawa ON K1A ON4 Ottawa ON KiA ON4 Canada Canada Vwr Ne Vmre Rfcimce Our 6k Notre reterence The author has granted a non- L'auteur a accordé une licence non exclusive licence dowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sel1 reproduire, prêter, distribuer ou copies of this thesis in rnicrofonn, vendre des copies de cette thèse sous paper or electronic formats. la fome de microfichelfilm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. An Application of Active Congestion Control in TCP-Vegas Abdoilah Aghassi Master of Applied Science, 2000 Department of Electrical and Cornputer Engineering University of Toronto Abstract TCP-Vegas, with its innovative congestion avoidance technique. achieves a better link utilization than other TCP vaiants. However, it fails to fairly allocate the available bandwidth arnong the usen. In particular, it penalizes the old connections in favor of the new connections. Furthemore, TCP-Vegas has the potential to induce persistent congestion in the network. These drawbacks al1 stem from the problem of over- estimation of propagation delay. To improve the faimess performance of TCP-Vegas, this thesis proposes a probing mechmism based on the active networking approach. The mechanism requires support from the active network nodes to immediately forward the probe packets. The acknowledgments of probe packets at the sender provide a better estimate of the propagation delays. Our simulation resuits show that our proposed active TCP-Vegas fairly allocates the bandwidth arnong the connections. In addition, the better estimation of propagation delays leads to reduced packet backiog in the buffer, and hence results in a lower level of network congestion than the original TCP-Vegas. Acknowledgement 1 would like to express my sincere gratitude and appreciation to my supervisor, Professor A. Leon-Garcia, for his invaluable guidance, patience, advice and encouragement throughout the course of my M.A.Sc. program and preparation of this thesis. 1 would dso like to thank Professor 1. F. Blake, Professor J. Choe, Professor E. Law and Professor S. W. Davies for their advice and comments dunng my final oral presentation. I wish to acknowledge in particular my fellows and friends in the Communications group for their fruitful discussion and proof-reading of the thesis. The financial support from ITRC is gratefully acknowledged. Table of Contents 1. INTRODUCTION................................................................ 1 1.1 Motivation ................................................................................. -3 1.2 Objective .................................................................................... 4 1.3 Thesis Organization ...................................................................... S 2. TCP CONGESTION CONTROL OVERVIEW ...........................7 2.1 Introduction ................................................................................ .8 2.2 Problems with Current TCP Implementation .......................................... 9 2.3 Proactive Congestion Control .......................................................... 10 2.3.1 Vegas Congestion Avoidance Mechanism ................................12 2.4 Major Drawback of Delay-Based Congestion Control Algorithrns ...............14 2.4.1 Errors in Round Trip Delay Mesurement .................................14 2.5 TCP-Vegas Pro blems .................................................................... 15 2.5.1 Unfairness...................................................................... 16 2.5.2 Persistent Congestion .........................................................31 3. ACTIVE NETWORKlNG and CONGESTION. ...................... 24 3.1 Introduction.............................................................................. 25 3.2 Explonng the Network by Smart Packets .............................................28 3.2.1 In-Band and Out-Band Monitor Packets.. .................................30 3.3 Major Drawbacks of the Active Networking Appronch ............................32 4 . ACTIVE CONGESTION CONTROL..................................... 34 4.1 Introduction ............................................................................... 35 4.2 Enhanced TCKVegas ................................................................... 36 4.2.1 Faimess Evduation of Enhanced Vegas ................................... 36 4.3 Vegas and DRR at the Gateway ........................................................ 40 4.4 Active Vegas ..............................................................................41 4.4.1 Preliminary Simulations ...................................................... 43 4.4.2 Single Bottleneck Network Simulations ................................... 45 4.4.2.1 Round Trip Time Measurement ...................................... 51 4.4.2.2 Fairness Evaiuation .................................................... 52 4.4.2.3 Buffer Occupancy ......................................................54 4.4.2.4 Sumqof Simulation Results ....................................-55 4.4.3 Multi-hop Network Simulation.............................................. 56 5.1 Discussion ................................................................................. 61 5 -3 Draw backs ................................................................................62 5.3 Future Research Directions ............................................................. 63 5.4 Research Contributions.................................................................. 64 List of Figures Figure 2.1. General pattern of round trip time vs . window size ................................ 8 Figure 2.2. Window algorithm of TCP.Vegas .................................................. 13 Figure 2.3. Network mode1 ........................................................................ 16 Figure 2.4. Simulation results when C = 0.5Mbps ............................................. 19 Figure 2.5. Network topology after the new connection joins the network ................ ..20 Figure 2.6. Simulation results after the new connection joins the network ..................20 Figure 2.7. Congestion window for each connection ......................................... .--33 Figure 3.1. Traditional passive network pmdigm ............................................ 25 Figure 3.2. Active network pattern ............................................................... 26 Figure 4.1: Connection goodputs and instantaneous queue lengths for enhanced Vegas.38 Figure 4.7: Connection podputs and congestion windows for old and new connections39 Figure 4.3. Packets in transit for active Vegas ................................................. .42 Figure 4.4. Priority queue at the gateway ........................................................ 42 Figure 4.5. Network mode1 ....................................................................... -43 Figure 4.6. Connection goodputs for 3 active Vegas sources................................. 44 Figure 4.7. Connection goodputs for 4 active Vegas sources ................................. 45 Figure 4.8. Network topology .................................................................... -46 Figure 4.9. Goodput vs . connection index for 4 different scenarios.......................... 47 Figure 4.10. Buffer occupancies for the different scenarîos.................................. .48 Figure 4.1 1: Mean goodput of each connection under different Vegas algorithm ........ A9 Figure 4.12. Buffer occupancy for original Vegas (infinite buffer size)..................... 50 Figure 4.13. Connection BaseRï73 for ail scenarios ........................................... 51 Figure 4.14. Faimess vs . bottieneck link bandwidth (link delay = 20msec) ................53 Figure 4.15: Faimess vs . bottleneck Iink propagation delay (link capacity = 4Mbps). -34 Figure 4.16. MuIti-hop network mode1 ........................................................... 56 Figure 4.17. Average congestion windows for different connections........................ 57 Figure 4.18. Goodput vs . connection index for active and original Vegas ..................58 List of Tables Table 4.1 : Connection throughput for 3 different versions of Vegas ........................ 44 Table 4.2. Buffer occupancies for 4 different implementations of Vegas ................... 55 Table 4.3. Summary of simulation results .................................................... -35 Table 4.4. BaseRTT estimation for active and original Vegas .................................59 vii List of Acronyms AACC Adaptive Admission Congestion Control ACC Active networking Congestion
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