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Chapter 6Optimisation of CRA using adaptive CSAs pOn high traffic loads, with this enhanced CSA only the contention slots needed toresolve the collisions are sent, allocating on average from 2.821 to 2.783 per request(according to the current traffic load), as shown in Figure 6.8, optimising further thebandwidth to be allocated to the reservation and contention-based access regions. InAverage umber of ContentionSlots per Request4.54.3Simple-CSA (CSs_3)Simple-CSA (CSs_5)4.1Forced-CSA (FSs_2,CSs_2)3.9Forced-CSA (FSs_2,CSs_3)V ariable-CSA -(CSs_2)3.7V ariable-CSA -(CSs_3)3.53.33.13 M bps Ups tream32 kbps Kbps IP IP &&2.99.7 kbps Kbps VoIPBackoff CRA2.729 30 31 32 33 34 35 36 37 38 39 40umbe r of Active StationsFigure 6.8 – Average No. of CSs per reservation request vs. No. of active stations.Exponential backoff algorithm with varying CSA applied.Mean Access Delay (ms)1000900800700600500400300200Simple-CSA(CSs-3)Simple-CSA(CSs-5)Forced-CSA(FSs-2,CSs-2)Forced-CSA(FSs-2,CSs-3)Variable-CSA(CSs-2)Variable-CSA(CSs-3)3 Mbps Upstream32 Kbps kbps IP IP &9.7 Kbps kbps VoIPBackoff CRA100031 32 33 34 35umber of Active StationsFigure 6. 9 – Mean access delay vs. No. of active stations.Exponential backoff algorithm with varying CSA applied.6-15
Chapter 6Optimisation of CRA using adaptive CSAs pCumulative Probability1.00.90.80.70.60.50.40.30.20.10.03 Mbps Upstream32 Kbps kbps IP &9.7 Kbps kbps VoIPBackoff CRA33 67 100 133 167 200 233 267 300 333 367 400 433 467 500Mean Access Delay (ms)terms of packet delays and number of streams supported, from Figures 6.9 and 6.10, thelowest access delays were gained using the Forced-CSA.For instance, with 45% of the channel capacity (produced by 33 stations), tolerablemean access delays for VoIP streams (under 50 ms) were seen only with Forced-CSA(FSs-2, CSs-3), supporting up to 33 stations. With a slightly increase in offered load(e.g. 46% produced by 34 stations), only the Simple-CSA (CSs-5) and the Forced-CSA(FSs-2, CSs-3) yielded tolerable low delays for the support of IP traffic.Approximately 73% of all data packets were transmitted in less than 200 ms asillustrated in Figure 6.10. The Simple-CSA (CSs-5) produced relatively low packetaccess delays because it sent more CSs than currently needed to resolve collisions,resulting in a reduction on the average CRGC. On the other hand, the Simple-CSA (CSs-5) wasted many CSs, trying to minimise the CRGC and therefore a slight decrease insystem throughput was obtained.Simple-CSA (CSs-3)Forced-CSA (FSs-1,CSs-3)Forced-CSA (FSs-2,CSs-3)Simple-CSA(CSs-5)Fo rced-CSA(FSs-2,CSs-2)Variable-CSA(CSs-2)Figure 6.10 – Cumulative probability vs. No. of active stations.Exponential backoff algorithm with varying CSA applied.Offered load = 46% produced by 34 stations.As a final remark for this section, in general the Forced-CSA outperforms the other twomechanisms (Simple and Variable-CSA). The Forced-CSA not only provided the lowestaccess delays, but also in most of the cases simulated provided the highest system6-16
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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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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 preserva
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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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