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Chapter 6Optimisation of CRA using adaptive CSAs pLarger values, (above 4 CSs per signalling frame) cause a waste of bandwidth, since theCSA tends to allocate more contention slots than those needed. This in turn results in areduction in system throughput. Furthermore, this causes increased access delay asstations transmit reservation requests more frequently. Such requests at the headendhave to wait longer for grant since there is a reduction in the bandwidth assigned forreservation access.From Figure 6.3, it is evident that on high traffic offered loads, beyond 50% of the cc,(generated by at least 24 stations), the average number of contention slots needed perrequest ranged from 3 to 3.5 slots, when the minimum number of CSs per signallingframe was below 5 slots.In Figure 6.2 we can appreciate that the maximum system throughput achieved wasapproximately 51% (for CSs-4) with an offered load about 52% of the channel capacityyielded by 25 stations. This difference of approximately 1% between theoretical andsimulation results was attributed to the fact that the CSA assigned on average 3.08contention slots per successful request (see Figure 6.3), instead of the optimum value of2.718. Furthermore, the average Pk size (registered by simulations) was 374 bytes with8.42 slots requested per packet, which made the difference of 1%.Average umber ofContention Slots per Request7.57.06.56.05.55.04.54.03.53.02.5CSs-1CSs-2CSs-3CSs-4CSs-5CSs-6CSs-73 Mbps Upstream64 Kbps kbps IPBackoff CRA18 19 20 21 22 23 24 25 26 27 28 29 30umber of Active StationsFigure 6.3 – Average No. of CSs per reservation request vs. No. of active stations.Exponential backoff algorithm with a Simple-CSA.6-5
Chapter 6Optimisation of CRA using adaptive CSAs p6.2.2.2 Splitting tree algorithm performance using a Simple-CSAFor this algorithm, the maximum theoretical bound for the system throughput can nowbe obtained by using Equation 4.44, in which reservation requests are transmitted usingminislots (MSs) of 21 bytes. The maximum theoretical system throughput that can beachieved with the splitting tree algorithm is ≈ 63% of the channel capacity, as shownbelow.SPk368.1== 62.6% ≈ 63+ eMSs 8.3*64 + 2.718* 21max=%PkslotsFrom simulation results shown in Figures 6.4 to 6.6, it is evident that the highest systemperformance is yielded with at least 1 CSs per signalling frame. This performance isachieved because a contention slot is reserved in the next signalling frame when acollision happens. This slot (which will be divided into three minislots) is then usedamong stations that caused the collision. By reserving an additional contention slot aftera collision, apart from the Min. o. of CSs per signalling frame, the Contention-Resolution-Grant Cycle (described in Section 3.4.1) is considerably decreased, thusresulting in a reduction in access delay.Mean Access Delay (ms)50045040035030025020015010050CSs-0CSs-1CSs-2CSs-3CSs-4CSs-5CSs-63 Mbps Upstream64 Kbps kbps IPTree CRA018 19 20 21 22 23 24 25 26 27 28 29 30 31umber of Active StationsFigure 6.4 – Mean access delay vs. No. of active stations.Splitting tree algorithm with a Simple-CSA.6-6
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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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