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Chapter 5Upstream channel capacity and characterisation pthe cc).As a final analysis, Table 5.5 presents a summary of the maximum system performanceand bandwidth characterisation for the six different packet sizes considered. In this tablewe can appreciate that regardless of the packet size, the maximum system utilisation isaround 89-90% of the link capacity, with a maximum deviation betweenthroughput/utilisation of ≈ 55% and ≈ 24% for minimum and maximum Ethernet packetsizes, respectively. There are several factors that may account for these deviations.A major component is due to the relatively large amount of overhead involved at MAC(ATM encapsulation) and PHY (forward error correction and synchronisation) layers.This can be as large as 34% and 23% of the cc when delivering small and large packetsof 64 and 1518 bytes, respectively.Another factor is the amount of bandwidth used for the transmission of successfulreservation requests. For 64-byte packets, this amount of bandwidth (of ≈ 12%)represents a significant portion of cc. However, for 1518-byte packets, this bandwidth(of ≈ 1%) represents a tiny fraction of the link capacity. This difference is because shortmessages require proportionally more reservation requests in order to transmit the sameamount of data than with larger messages. For instance to transmit 32 kbps, a stationwill send 75 requests per second with a 64-byte packet size, in comparison to 2.64requests per second with a 1518-byte packet size.Table 5.5 - Maximum system performance and bandwidth characterisation.BandwidthPacket size (bytes)Characterisation (%) 64 128 256 512 1024 1518Maximum throughput 34.5 51.3 56.2 62.9 63.4 64.6Maximum utilisation 89.1 90.1 90.5 89.8 88.9 88.5Deviation 54.6 38.8 34.3 26.9 25.5 23.9Supported streams 25.0 48.0 54.0 60.0 60.0 63.0Request collided 8.3 4.1 1.3 0.4 0.1 0.1Request successful 11.8 8.5 4.6 2.6 1.3 0.9MAC&PHY overhead 34.5 26.2 28.4 23.9 24.1 23.0Bandwidth unused 10.9 9.9 9.5 10.2 11.1 11.55-35
Chapter 5Upstream channel capacity and characterisation pThe next significant factor, as stated earlier, is the bandwidth wasted by unsuccessful(or collided) reservation request, which can result in a significant amount when shortmessages are delivered.Finally, the other obvious performance issue is the inability of the system to reach themaximum channel capacity (≈ 100%). The reason for this is the minimum number ofcontention slots allocated per signalling frame, which was set to 2 in this scenario (andaccounted for ≈11% cc).For 1518-byte packets, some additional CSs were added to the signalling frame becauseof the inability of the headend to allocate all reservation slots for the transmission ofdata packets. Hence, the total bandwidth allocated to the contention access region(registered by simulations) accounted for ≈12% of the link capacity, where only ≈ 1%was used for successful and unsuccessful requests and the other bandwidth, of 11%,remained unused.In general, the unused bandwidth can be reduced by decreasing the number of CSsallocated per signalling frame. However, this may be inefficient for short packet sizes,and particularly when the exponential backoff algorithm is used, as examined in theSections 5.4.2 and 5.4.4.We have also carried out a detailed performance analysis of isochronous streams (at8kbps, 16 kbps, 32 kbps, 64 kbps and 128 kbps) for a 6 Mbps upstream channel and sixdifferent packet sizes (64, 128, 256, 512, 1024 and 1518 bytes). This analysis isreported in [85] and presented in Figure E.2 of Appendix E.5.5 ConclusionsIn this chapter, four novel and topical traffic types were used to analyse the fundamentalperformance characteristics of DVB/DAVIC compliant networks with the use of asimulation model. This data facilitates further optimisations and enhancements in theprotocol development of DVB/DAVIC. We studied key issues on system performanceusing both contention resolution algorithms, such as: packet access delay and maximumthroughput that can be achieved by a single station; packet size scalability, optimisation5-36
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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 3THE DVB/DAVIC PROTOCOL3.1
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Chapter 3The DVB/DAVIC protocol pEu
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Chapter 3The DVB/DAVIC protocol pMA
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Chapter 3The DVB/DAVIC protocol pTh
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Chapter 3The DVB/DAVIC protocol p3.
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Chapter 4Simulation and analytical
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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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