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Chapter 4Simulation and analytical modelling pWe have proved that simulated performance of the system does not depend on the seedused, therefore it will not be mentioned again and all simulation results presented in thefollowing chapters will be yielded using a seed of 257.For a larger number of nodes, we also carried out a rigorous verification test of theoperation of the DVB/DAVIC simulation model. For this test, we used a mixed trafficpattern consisting of 32 kbps IP traffic and 9.7 kbps VoIP traffic (these traffic types aredescribed in Section 5.4), using the exponential backoff algorithm. We ran a simulationfor 60 seconds and captured the sequence of events between the 59 th and the 60 thsecond. Appendix D shows this sequence for 30 stations. From analysing these eventswe can verify that every station transmitted all packets received and used the contentionresolution algorithm correctly. On average, every station received (1/(0.092 IP interarrival+ 0.12 VoIP inter-arrival) = 19.6 packets per seconds, which corresponds to thenumber of packets received and transmitted in Appendix D.4.6 ConclusionsThe DVB/DAVIC protocol is a relatively new specification and little information aboutits performance and scalability is known. In this chapter, the suitable simulation andtheoretical models have been presented. These models will be used in subsequentchapters for the performance evaluation, optimisations and enhancements of theDVB/DAVIC protocol.The simulation model implemented for this research was based on the main networktopology of the CSF (v.13), developed by MIL3, Cablelabs and the University ofSheffield. This model has been significantly modified to support the basic functionalityof the MAC and PHY layers of the DVB/DVIC protocol, including the functionality ofthe two contention resolution algorithms adopted by the DVB/DAVIC protocol. Inaddition, new features for further optimisations were also incorporated in the simulationmodel, such as contention slot allocators, enhanced reservation requests mechanisms,and a prioritised scheduler, which will be used in subsequent chapters.Existing analytical models from the literature were insufficient to model theDVB/DAVIC protocol, as they did not take into account the variable bandwidth of the4-35
Chapter 4Simulation and analytical modelling pcontention-based access region and the performance of the exponential backoffalgorithm or the splitting tree algorithm. A less complicated theoretical model has beenformulated for the purposes of validation of the simulation model. Such a model wasbased on an M/G/1 queuing system for a single node scenario. This model addressedone of the fundamental performance properties of computer communications protocols,which relates to the mean packet access delays and maximum sustainable throughput ofa station.Results obtainable using the simulation model for the DVB/DAVIC protocol were ingood agreement with theoretical results, with a maximum deviation of 4% for meanaccess delays and 2% for throughput. We also found that the DVB/DAVIC protocol ishighly inefficient when short data packets are transmitted, achieving only ≈ 224 kbps(≈ 4% of the channel capacity) when 64-byte packets are delivered.For a larger number of nodes, we have also provided some theoretical bounds that couldbe used to estimate the maximum system throughput sustainable by the DVB/DAVIC’supstream channel for different traffic loads and protocol configurations.4-36
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I would like to thank all the peopl
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CHAPTER 6: OPTIMISATIO OF CRA ALGOR
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FIGURE 5.17 - SYSTEM THROUGHPUT VS.
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LIST OF TABLESTABLE 2.1 - NEXT GENE
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Chapter 1Introduction pBecause of h
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Chapter 1Introduction pA first step
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Chapter 1Introduction passumption i
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Chapter 1Introduction ppolynomial b
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Chapter 1Introduction pIn general,
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Chapter 1Introduction pminislots to
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Chapter 1Introduction pThe authors
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Chapter 1Introduction prate access
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Chapter 1Introduction p1.4 Overview
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Chapter 2OVERVIEW OF CURRENT CATVNE
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Chapter 2Overview of current CATV n
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Chapter 6Optimisation of CRA using
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Chapter 7PERFORMANCE OPTIMISATION F
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Chapter 7Performance optimisation f
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aChapter 7Performance optimisation
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Chapter 8Final conclusions p8.2 Gen
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Chapter 8Final conclusions pWe have
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Chapter 8Final conclusions pperform
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Chapter 8Final conclusions pslots i
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Chapter 8Final conclusions pfocused
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Chapter 8Final conclusions preserva
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Chapter 8Final conclusions pbandwid
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Chapter 8Final conclusions pThe opt
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Chapter 8Final conclusions p8.4 Fut
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Chapter 8Final conclusions pApplica
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Chapter 8Final conclusions pTCIS st
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Referencesp[17] I. Cidon, and M. Si
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Referencesp[50] N. F. Huang, C. A.
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Referencesp[85] V. Rangel, R. Edwar
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Referencesp[112] K. Sriram, “Meth
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APPEDIX A: GLOSSARYAALABRADSLATMBCB
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Appendix AGlossary pkbpsLANLLCMACMA
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Appendix AGlossary pUSBUWVDSLVoDVoI
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Appendix BProtocol stack and packet
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Appendix BProtocol stack and packet
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APPENDIX C: D VERIFICATION TEST FOR
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Appendix D Verification test p209 2
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Appendix EResults for a 6 Mbps upst
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Appendix FGuide to CD-ROM p IEEE802
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