D esign Issues IN Q uality of S ervice R o u t in g By Karol Koivalik T h e sis d ir e c t e d by: D r . M a r t in C o l l ie r A THESIS PRESENTED FOR THE AWARD OF D o c t o r o f P h i l o s o p h y January 2004 Sc h o o l o f E l e c t r o n ic E n g in e e r in g D u b l in C ity U n iv e r s it y / hereby certify that this material, which I now submit for assess­ ment on the programme of study leading to the award of Doctor of Philosophy is entirely my own work and has not been taken from the work of others save and to the extent that such work has been cited and acknowledged within the text of my work. Signed: ID number: 50161172 Date: 11/12/2003 Abstract The range of applications and services which can be successfully deployed m packet-switched networks such as the Internet is limited when the network does nor provide Quality of Service (QoS) This is the typical situation in today's Inter­ net A key aspect m providing QoS support is the requirement for an optimised and intelligent mapping of customer traffic flows onto a physical network topol­ ogy The problem of selecting such paths is the task of QoS routing QoS routing algorithms are intrinsically complex and need careful study before being imple­ mented in real networks Our aim is to address some of the challenges present m the deployment of QoS routing methods This thesis considers a number of practical limitations of existing QoS routing algorithms and presents solutions to the problems identified Many QoS routing algorithms are inherently unstable and induce traffic fluctuations in the network We describe two new routing algorithms which address this problem The first method - ALCFRA (Adaptive Link Cost Function Routing Algorithm) - can be used in networks with sparse connectivity, while the second algorithm - CAR (Connectivity Aware Routing) - is designed to work well in other network topolo­ gies We also describe how to ensure co-operative interaction of the routing algo­ rithms in multiple domains when hierarchial routmg is used and also present a solution to the problems of how to provide QoS support m a network where not all nodes are QoS-aware Our solutions are supported by extensive simulations over a wide range of network topologies and their performance is compared to existing algorithms It is shown that our solutions advance the state of the art in QoS routing and facilitate the deployment of QoS support m tomorrow's Internet Acknowledgements Several people supported me through my study and I would like to thank them all First of all I would like to thank my supervisor, Dr Martin Collier, who has continually motivated and supported me through my time at DCU I am very grateful to him for giving me the right mix of freedom and guidance Also I thank him for correcting errors in my English and his patience with my complete lack of understanding of definite and indefinite articles I wish to thank Prof Charles McCorkell, Dr Noel Murphy and Prof Jon Crowcroft for serving on my doctoral committee and for their comments and suggestions I am also grateful to Switching and Systems Lab members for their friendship and advice Especially I thank Kalaiarul Dharmalmgam for discussions and col­ laboration I'm grateful to many other faculty members at DCU for their words of advice I thank my parents for their well wishes and blessings I thank all my friends Finally I thank Agnieszka Scheller for always believing in me List of Publications • K Kowalik AND M COLLIER, QoS routing as a tool of MPLS Traffic Engi­ n eerin g m First Joint IEI/IEE Symposium on Telecommunications Systems Research, Dublin, Ireland, November 2001 • K Kowalik and M Collier, ALCFRA - A Robust Routing Algorithm Which Can Tolerate Imprecise Network State Information, in Proceedings of 15th ITC Specialist Seminar, Wurzburg, Germany, July 2002, pp 39^45 • K Kowalik a n d M C o l l i e r , Should QoS routing algorithms prefer shortest paths7, m Proceedings of IEEE 2003 International Conference on Communi­ cations, vol 1, Anchorage, Alaska, May 2003, pp 213-217 • K K o w a lik AND M C o l l i e r , Connectivity Aware Routing - a method for finding bandwidth constrained paths over a variety of network topologies, in Pro­ ceedings of IEEE Symposium on Computers and Communications, An­ talya, Turkey, June 2003, pp 392-398 • K Dharmalingam, K Kowalik, a n d M C o l l i e r , RSVP Reservation Gaps Problems and Solutions, m Proceedings of IEEE 2003 International Conference on Communications, vol 3, Anchorage, Alaska, May 2003, pp 1590-1595 • K Kowalik a n d M C o l l i e r , Methods for Reducing Traffic Fluctuations of Link State QoS Routing Algorithms in Virtual Circuit Networks, submitted to IEEE/ACM Transaction on Networking • K Kowalik AND M COLLIER, Coexistence of various topology aggregation methods in a hierarchical network, submitted to IEEE Symposium on Comput­ ers and Communications • K Dharmalingam, K Kowalik, and M Collier, RSVP Reservation Gaps Problems and Solutions, submitted to Elsevier Computer Communica­ tions CONTENTS List of Figures v List of Tables x 1 Introduction 1 1 1 QoS and routing 2 1 2 Thesis contribution 3 121 Problem statement 3 12 2 Methodology 3 12 3 Solutions 4 1 2 4 Summary of Contributions 6 1 3 Organisation of the Thesis 6 2 QoS Routing 8 2 1 The story of QoS routing 9 211 Routing m telephone networks 10 212 ARPANET Routing 11 213 Internet Routing 13 214 Routing m ATM Networks 16 2 2 Challenges of QoS routing 20 2 21 Computational cost 21 2 2 2 Communication cost 22 2 2 3 Inaccuracy 2 2 2 2 4 Instability 23 2 2 5 Other QoS routing challenges 26 2 3 Different approaches to QoS routing 27 l CONTENTS 2 31 Centralised vs distributed computation 27 2 3 2 Local vs global state information 28 2 3 3 Source routing vs hop-by-hop routing 28 2 3 4 Rerouting 29 2 4 Route computation algorithms 29 2 41 Relaxation 30 2 4 2 Bellman-Ford algorithm 31 2 4 3 Dijkstra algorithm 32 2 5 QoS Routing algorithms 33 2 51 The resource conserving approach (RC) 35 2 5 2 The load distributing approach (LD) 36 2 6 Optim al Routing 37 2 61 Theoretical formulation of Optimal Routing 38 2 6 2 Optimality condition 3 9 2 6 3 Optimal routing used in off-line optimisation 40 2 6 4 On-line suboptimal routing 44 2 7 Related topics 49 2 71 Traffic Engineering and Constraint Based Routing 49 2 7 2 Admission Control 52 2 73 Resource Reservation 52 2 7 4 Integrated Services and Differentiated Services 53 2 7 5 Integrated Services over DiffServ Networks 56 2 7 6 MPLS 57 2 7 7 Active Networks 58 2 8 Summary 59 3 Model for QoS routing 60 3 1 Routing algorithms 61 311 Network model 62 3 1 2 Link cost 62 3 2 Network Topology 64 3 3 Traffic model 67 3 4 U pdate policies 6 8 3 5 Performance metrics 70 3 6 Summary 71 4 QoS Routing Theory Vs Practice 74 4 1 Instability of the Load Distributing approach 75 411 Estimation Error 76 n CONTENTS 412 Link Cost Sensitivity 77 413 Network response 79 414 Instability of the LD approach Summary 89 4 2 Load Distribution (LD) vs Resource Conservation (RC) 89 4 21 Performance evaluation of LD and RC approaches 90 4 3 Summary 96 5 Methods for Damping Traffic Fluctuations 98 51 ALCFRA 99 5 11 The basics of ALCFRA 100 512 Adaptation of the link cost function m ALCFRA 101 513 ALCFRA Link Cost Sensitivity 103 514 ALCFRA first derivative 105 5 15 ACLFRA performance evaluation 107 516 The tuning of ALCFRA 113 517 ALCFRA summary 116 5 2 Connectivity Aware Routing (CAR) 116 5 21 CAR details 117 5 2 2 CAR Link Cost Sensitivity 120 5 2 3 CAR performance evaluation 121 5 3 Summary 130 6 Problems m the deployment of QoS routing 132 6 1 Coexistence of various topology aggregation methods 133 611 Aggregation methods 134 612 Aggregation strategies 135 613 Performance evaluation 136 6 2 Reservation gaps 142 6 2 1 Performance evaluation 144 6 3 Summary 150 7 Conclusions 152 71 Contributions 153 7 2 Future Work 155 7 3 Concluding Remarks 157 Appendices 158 in CONTENTS A FREDA a routing algorithm for terabit switches 158 A 1 FREDA modification 162 A 2 Summary 164 Index 166 Bibliography 169 IV LIST OF FIGURES 2 1 An example of the hierarchical structure used m PNNI 18 2 2 Examples of PNNI topology aggregation methods 19 2 3 An example when the shortest path approach performs poorly 36 3 1 Link cost function of the WSP algorithm 63 3 2 Link cost function of the EXP algorithm 64 3 3 Topologies used in simulations 6 6 4 1 Link Cost Sensitivity of the LD approach 78 4 2 Cost <—> utilisation mapping cycle 80 4 3 Examples of network response for a highly utilised link 80 4 4 Examples of network response for a lightly utilised link 81 4 5 Stable area of network response 82 4 6 Unstable areas of network response 83 4 7 Observed and typical areas of network response 83 4 8 Average network response 84 4 9 Link cost for a link with high utilisation 85 4 10 Typical areas of network response for a link with high utilisation 8 6 4 11 Average network response for a link with high utilisation 8 6 4 12 Unstable link cost«— »utilisation trajectory for a link with high util­ isation 87 4 13 Link cost for a link with low utilisation 87 4 14 Typical areas of network response for a link with low utilisation 8 8 4 15 Average network response for a link with low utilisation 8 8 416 Stable link cost«— >utilisation trajectory for a link with low utilisation 89 LIST OF FIGURES 4 17 Call blocking probability of WSP and EXP versus increasing node degree, p = 0 3, hd — lsec 93 4 18 Call blocking probability of WSP and EXP versus increasing node degree, p — 0 3, hd — 40sec 94 4 19 Call blocking probability of WSP and EXP versus increasing