U - b-Ît Real-Time Communications in Token Ring Networks by Li-Jun Yao A thesis submitted for the degree of Doctor of PhilosoPhY TN Department of ComPuter Science The [Jniaersi,tY of Adelaide Jairuary L994 \1q Au,o, ltJ \' Abstract as it imposes a Real-time communications differ from traditional data communications It is weil known that time constraint, such as d,ead,line, on each message transmission' for task scheduling in a the Earliest Deadline First (EDF) scheduling policy is optimal policy in a distributed centralized real-time system. However, implementing the EDF real-time environment real-time system is d.ifferent from its counterpart in a centralized work deals with the due to its non-negligible scheduling overhead involved. This distributed system implementation of the EDF policy in the context of a speciflc - a token ring a token ring local area network. Its main objectives are (i) to propose real-time message protocol which implements the exact network-wide trDF policy for level of transmission, and. (ii) to address the fundamental issue of the appropriate environment' implementing an optimal scheduling poiicy in a distributed real-time In brief, the work is concerned with the design and performance evaluation of implement variations three token ring protocols for real-time communications' which is an existing token of the EDF. transmission policy with different overheads. The flrst overhead' passingprotocol which does not adhere to the EDF poiicy but has a minimal the EDF policy The second is a modified priori,ty-ilriuen protocol which approximates for with a moderate overhead. The third is the window protocol which is proposed ll the exact EDF transmission the token ring networks for the first time' It implements high' policy, but its contention overhead may be potentially and compared' It The worst case performance of the three protocois is analyzed protocoi is determined is found that the pert'ormance of a distributed communication overhead not oniy by the transmission policy employed, but also by the contention that no protocol can incurred when implementing such a policy' It is also shown langes considered and that always outperform the others for the entire parameter performance is the best' each protocol has its own applicable region where its protocols is evaluated Furthermore, the average case performance of the three ring network through simulation. It is found that under the current token best performance as a result technology, the proposed window protocol achieves the when the ring gets of implementing the EDF policy. However, it is also shown that is reduced' faster, the difierence in the performance of the three protocols algorithm, Therefore, it is concluded that in designing a distributed scheduling in achieving an optimai such as a communication protocol, one should seek a balance scheduling policy and minimizing the scheduling overhead. Ill Acknowledgments to my former supervisor I wish to express my deep gratitude and appreciation guidance, support and Prof. wei zhao lor suggesting this project and for his devoted my coming help. I am very grateful to Prof. chris Barter for having facilitated support and to Australia to und.ertake this research and for his immense enthusiasm, Zukerman for expanding my encouïagement as my later supervisor. I thank Dr. Moshe the Network Analysis section' research horizon tremendously when I was working in cheng-chew Lim from Telecom Research Laboratories in 1991. I also thank Dr' heipful advice and the Department of Eiectricai and Electronic Engineering for his comments. but near I am deeply indebted to my parents and my sister who are remote thanks to and whose love, und.erstanding and support are invaluable' Special and bad piero Ammirato for his love and support and for sharing the good times introduced Australia to me times over the past four years. I thank Fred Thornett who me. Finally, I am thankful to seven years ago for his friendship, help and confldence in one way or another ali the staff members in the d.epartment and all my friends who in have contributed to the making of this thesis' This work was supported. by the univerity of Adelaide Postgraduate Research Scholarship. v Contents l1 Abstract iv Declaration v Acknowledgments 1 Introduction 1 1 1.1 Motivation and ScoPe 6 1.2 Real-Time Communications I.2.1 Definitions and Objectives 6 8 I.2.2 Selection of the Optimal Algorithm 10 1.3 Reiated Work 1.3.1 Related CSMA/CD Based Work 10 1.3.2 Related Token Bus/Ring Based Work 13 T7 I.4 Desirable Properties of Protocols for Real-Time communications ' 18 1.5 Thesis Outline 20 2 System Models 20 2.1 Network Model 23 2.2 Network Parameters V1 2.3 Message Model and Parameters 2.4 Protocol Notations and Performan.ce Metrics 2.5 Methodoiogy for Worst Case Performance Analysis 3 The Token Passing Protocol 3.1 Protocol DescriPtion 3.2 Protocol ProPerties 3.3 Worst Case Performance Analysis 3.4 Numerical Results and Discussions 4 The PrioritY-Driven Protocol +J Protocol DescriPtion 4.2 PrioritY Assignment Function 4.3 Worst Case Performance of PD*sP 4.3.1 Lower Bound of R(PD*>p,u,n) 4.3.2 UPPer Bound o1 R(PD*>n',u,n) 4.3.3 An Estimation of R(PD*>D,u,n) 4.g.4 Numerical Results and Discussions 4.4 Worst Case Performance of- PD^<a +.4.I Worst Case Performance Ratio R(PD*a¿,w,n) 4.+.2 Numerical Results and Discussions 4.5 Worst Case Performance of PD¿a*ap ' +.5.1 ProPerties of PD^<¿ 4.5.2 Performance bounds for Ak(n) 4.5.3 Numerical Results and Discussions 4.6 Enhancements and Modifications v11 L26 5 The Window Protocol t26 5.1 Basic ConcePts r27 5.2 Data Structures r27 5.2.1 Window Setting 130 5.2.2 Token Format t32 5.2.3 Data Structures on a Node t32 5.3 Protocol DescriPtion 5.3.1 Monitor Node 133 5.3.2 Non-Monitor Nodes 137 145 5.4 Worst Case Performance AnalYsis 150 5.5 Numerical Results and Discussions 151 b.0 Major Advantages of the Window Protocol t54 Ð.1 Protocol Realization t54 5.7.I Direct Realization ' 5.7.2 Optimal Realization 155 5.7.3 Practical Realization 161 L62 5.8 Enhancements and Modifications 5.8.1 Urgent Pre-emPtion. t62 5.8.2 Faster Deadline Tie Handling 166 167 5.8.3 Faster Resolution 169 5.8.4 Choice of Threshoid 169 5.8.5 Possible Realization . 6 'Worst Case Performance Comparison t70 6.1 Comparison Method 170 vrll 6.2 Pair-Wise ComParisons 6.3 Comparison of Three Protocols 6.4 AppticabilitY of Results 7 Average Case Performance Comparison 7.t Simulation Program 7.2 Traffic Model and Parameters 7.3 Performance Metrics 7.4 Simulation Resuits 7.4.I Effect of Offered Load 7.4.2 Efiect of Ring SPeed 7.4.3 Effect of Ring PoPulation 7.4.4 Effect of Protocol Parameters 7 -4-4.1 Effect of Number of Priorities 7.4.4.2 Effect of Length of Priority Assignment Function 7 -4.4.3 Effect of Initial Window Size 7.4.4.4 Effect of Initial Window Lower Bound 7.5 Discussions g conclusions and Recommendations for F\rture Research 8.1 SummarY of Results 8.2 Signifi,cance and Contribution 8.3 Recommendations for Future Research A Publications and Presentations References lx List of Tables 24 2.1 Network Parameters 137 5.1 Monitor Node Operations (trxplanatory Scheme) ' ' ' 138 5.2 Non-Monitor Node Operations (Explanatory Model) ' Scheme) 158 5.3 Encoding for Monitor Node Operations (Optimal scheme) . 159 5.4 Encoding for Non-Monitor Node operations (optimal scheme) . 163 5.5 Encoding for Monitor Node operations (Practical (Practical scheme) 164 ,5.C) Encoding for Non-Monitor Node operations 179 6.1 Performance Relationship in Six Regions 182 6.2 Range of Normalized Token Node-to-Node Delay 189 7.L Traffic Profrle r92 7.2 Effect of Offered Load Dq t97 1..) Effect of Ring SPeed 202 7.4 Effect of Ring PoPulation 2lr 7.5 Effect of Initial Window Lower Bound x List of Figures 2T 2.r Generic Real-Time Communication Layer Model 23 2.2 A Token Ring Network Ðt 3.1 Worst Case Performance Ratio of TP 64 4.1 A Priority Assignment Function 66 4.2 Time Diagram of Message Transmission ' 93 4.3 Worst Case Performance Ratio of PD*sp 93 4.4 Comparison of R¡o-, Ru, and R""t 103 4.5 Effect of the Number of Priorities 104 4.6 Worst Case Performance ratio of PD*<a t27 4.7 Effect of the Number of Priorities t22 4.8 Effect of Parameter Ie . t22 +.9 Worst Case Performance o'L PD¿a*aD ' t28 5.1 Initial Window Boundaries 130 5.2 Proposed Token Access (AC) Field t34 5.3 Protocol State Machine Transition Diagram r+2 5.4 Splitting of Window WPw 151 5.5 Worst Case Performance Ratio of WD t52 5.6 Effect of Number of Windows xl 153 5.7 Time Diagram for Message Transmission 161 5.8 IEEE 802.5 Token Format 173 6.1 Pair-Wise Equai Performing Bands 175 6.2 Pair-\Mise Equal Performing Curves 777 6.3 Comparison of Three Protocols 178 6.4 Comparison of Three Protocols 180 6.5 Comparison of Three Protocols 183 6.6 Parameter Range of Current Token Ring Networks 186 7.r Simulation Program Flow Chart ' ' ' 190 7.2 Token Access Controi Field Format 195 LJ Effect of Offered Load 199 7.4 Effect of Ring SPeed 201 7.5 Effect of Ring PoPulation 204 7.6 Effect of Number of Priorities 206 7.7 Effect of Length of Priority Assignment Function 208 7.8 Effect of Initial Window Size ' 2t0 7.9 Effect of Initial Window Lower Bound xll Chapter 1 Introduction 1-.1 Motivation and ScoPe over the last The need for high speed.