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Chapter 5Upstream channel capacity and characterisation pFigure 5.7 presents the total amount of data messages transmitted in the contentionbasedregion, and Figure 5.8 shows the bandwidth consumed by collisions. Results fromFigure 5.6 revealed that with a high offered load of 37% of the link capacity (generatedby 26 stations) only 36% was successfully transmitted when using a value of 1 ATMData Transmitted in theContention-based Region (%)242118151296303 Mbps Upstream32 Kbps kbps IP &12.4 Kbps kbps VoIPBackoff A lgorithmContention Msg Length -- 0 ATM CellContention Msg Length -- 1 ATM CellContention Msg Length -- 2 ATM CellsContention Msg Length -- 3 ATM CellsContention Msg Length -- 5 ATM CellsContention Msg Length -- 6 ATM Cells14 16 18 20 22 24 26 28 30 32umbe r of Active StationsFigure 5.7 – Data transmitted in the contention-based region vs. No. of active stationsfor different contention messages.Bandwidth Consumed by Collisions0.190.170.150.130.110.090.070.050.030.013Mbps Upstream32Kbps kbps IP IP & &12.4 Kbps kbps VoIPBackoff CRAContention Msg Length -- 0 ATM CellContention Msg Length -- 1 ATM CellContention Msg Length -- 2 ATM CellsContention Msg Length -- 3 ATM CellsContention Msg Length -- 5 ATM CellsContention Msg Length -- 6 ATM Cells14 16 18 20 22 24 26 28 30 32umber of Active StationsFigure 5.8 – Bandwidth consumed by collisions vs. No. of active stationsfor different contention messages.5-17
Chapter 5Upstream channel capacity and characterisation pcell for the ‘Contention Access Message Length’ parameter (the other 1% was queued inthe station’s buffer). From this 36%, only 14.5% (Figure 5.7) of the offered load wastransmitted in contention access, and the rest (21.5%) was sent using reservation access.In order to transmit the 1-ATM-cell messages and the reservation requests of the othermessages using contention access, Figure 5.8 reveals that 10.8% of the bandwidth wasconsumed by collisions. With a value of 5-ATM cells for the same parameter, thebandwidth consumed by collisions was reported in the order of 16% of the cc, whichresults in a loss in system throughput as seen in Figure 5.6.Thus, it can be noticed that as larger messages are allowed to be transmitted usingcontention access, the risk of collision is increased slightly. In the case that none of themessages were transmitted in contention access, it is obvious that with heavy trafficloads, the bandwidth consumed by collisions is minimised.5.4.4 Effects of reservation request sizeIn this analysis, we now address the case when stations only use reservation access forthe transmission of data messages. The analysis focuses on the impact on systemperformance when the maximum request size (or ‘Maximum Reservation AccessMessage Length’ as named in the specification) is ranged from 6 to 32 ATM cells. Thisconfiguration parameter specifies the maximum length of a message that can betransmitted using a single reservation request access. Any message greater than this istransmitted by making multiple reservation requests.When a station is enabled to use only reservation access for the transmission of datamessages, as the offered load increases, short packets tend to accumulate in the station’sbuffer. This is true even at lower loads depending on the traffic type. Large packets forsome applications may generate several (or many) ATM cells at once when segmentedinto 53-bytes chunks. If a station with a large packet is allowed to send only one requestfor the transmission of the complete packet, that may affect the transmissions of theother stations. This is because the headend serves the station’s reservation requests in aFIFO order regardless of the traffic type, and the larger the request size the higher thechannel access will be, which delays the other reservation request. This effect will beaddressed at the end of this section.5-18
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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 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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