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Chapter 6Optimisation of CRA using adaptive CSAs pFor the Forced Mini-Slots CSA, the authors found that by setting the number of forcedmini-slots to 2 instead of e, good results were obtained. In our analysis, we also foundthat by allocating 2 FSs, after a collision, an improvement in system performance wasobtained. Results for the Forced-CSA are presented in Section 6.2.3.3.6.2.3.2 Variable-CSA used with the exponential backoff algorithmThis mechanism uses a variable slot regime algorithm in which the ratio of CSs toreservation data slots (RSs) is varied from signalling frame to signalling frame, based onthe current traffic load, mean packet size and the mean of requested slots. Variable slotallocators have been used since 1998 in MAC protocols for HFC and wireless accessnetworks. They were firstly introduced in [112] and [113]. Later on, they were reportedin [41] for the IEEE 802.14 protocol. The mechanism presented here is similar to [41]with slight modifications for the DVB/DAVIC protocol. The variable number of CSs(VCSs) to be added in the signalling frame is dynamically adjusted as the headendconverts the number of RSs into CSs (N RSs) according to Equation 6.2. RSs=⎡2⋅⎢⎣ 2MAX+ Re_ DATA⎤q _ Size⎥⎦(6.2)where MAX_DATA is the maximum number of data slots that can fit in a signallingframe (= 18 – Min. o. of CSs per signalling frame, for a 3.088Mbps upstreamchannel) and Req_Size is the average number of RSs that can be requested at once.VCSs can be determined from Equation 6.3.⎧0if MAX_REQ ≥ α ⋅ (MAX_DATA - NRSs)VCSs = ⎨(6.3)⎩NRSselsewhere MAX_REQ is the total number of data slots requested but not yet allocated bythe headend, α is a design parameter set to 2.5 as suggested in [41]. The total number ofCSs to be included in the next signalling frame is then represented by followingparameters: the Min. o. of CSs per signalling frame (as proposed in the Simple-CSA),the variable number of CSs derived from Equation 6.3 and the unused RSs converted toCSs as recommended in [96] and [98] .6-11
Chapter 6Optimisation of CRA using adaptive CSAs p6.2.3.3 Performance comparison of Enhanced-CSAsIn order to provide a complete performance comparison between the Forced andVariable CSAs, three different traffic configurations will be analysed: 64 kbps IPstreams, 32 kbps IP streams and 41.7 kbps mixed traffic.A summary of the maximum system performance produced by each CSA for Internettraffic is presented in Table 6.2. A detailed comparison for mixed traffic is shown inFigures 6.7 to 6.10.For Internet traffic at 32 kbps per station, the best system performance was achieved bythe Forced-CSA. Three different configurations were analysed using this scheme (asindicated in Table 6.2). The highest system throughput (about 52% of the cc) and thelowest mean access delay (of 584 ms) was achieved by both allocating 2 FSs after acollision and defining at least 2 CSs per signalling frame, at approximately 53% of thechannel capacity (produced by 51 stations). In addition, the average number of CSsneeded per request resulted in 2.819, which is quite close to the optimum e(=2.718) witha maximum deviation under 1% of the cc between simulation and theoretical results.Table 6.2 – Maximum system performance for Internet traffic and different CSAs.InternetTraffic32 kbpsCSASimpleSimpleMin. CSsPer Sign.FrameMaximumThroughput(%)Mean AccessDelay(ms)CSs perRequestOfferedLoad(%)ActiveStations3 46.8 3099.98 3.96344 52.3501 515 48.0 2004.82 3.57891 51.3815 51Forced-FSs 1 3 51.1 1284.42 2.87358 53.1611 51Forced-FSs 2Forced-FSs 2VariableVariable2 51.5 584.026 2.81989 52.8379 513 51.0 1090.09 2.91893 53.0158 512 47.9 2628.13 3.68146 53.153 513 47.8 2195.96 3.6845 52.9651 5164 kbpsSimple 4 50.6 1226.38 3.07588 52.5 25Forced-FSs 1 3 50.7 913.49 3.01059 51.7 25Forced-FSs 2 2 50.6 494.56 3.01297 51.3 25Forced-FSs 2 3 49.8 416.05 3.15268 50.7 25Variable 2 50.8 777.72 2.95227 51.9 25Variable 3 51.3 624.79 2.87162 52.1 25The shaded rows present the CSA with optimum system performance.6-12
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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 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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