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Chapter 8Final conclusions pThe major drawback of using CATV networks for satellite communications, as seen inFigure 8.2a, is the long propagation link delays, which can result in serious performanceimplications.This is because very large propagation delays (in the order of hundreds of milliseconds)will results in equally large scheduler look-ahead delays. The propagation delay to theheadend and back in such systems will be twice the roundtrip delay to the satellite,which in the case of Geo-stationary Earth Orbit (GEO) satellites placed at about 22.3miles above the Earth would be of ≈ 500 ms [9]. Therefore the explicit CRGC cycle willresult in large intervals of network idle time due to the number of contention slots the schedulerwill have to subscribe.For delay sensitive applications, such as voice conversations, the propagation delay overthe two-way path between conversants influences the perceived quality of service. Thisproblem can be ameliorated with LEO satellites placed at ≈ 500 – 1000 miles above theEarth. This relatively short distance reduces transmissions delays significantly to ≈ 50ms [9]. The drawback is that a large number of satellites, arrayed on a constellation ofmultiple satellites in a polar orbit is required to maintain path continuity.The long propagation delays of satellite systems undoubtedly will reduce the systemefficiency of a CATV MAC protocol. An interesting issue requiring further research isto analyse to what extent long propagation delay can degrade the quality of service ofGEOBACKBONECity xPSTNCity yLEOFDDIDQDBMobile NodeISPMobile NodeHeadendHeadendMobile NodeMobile Nodea) Satellite Mobile/Fixed b) Digital CATV b) Terrestrial Mobile/ Fixed WirelessFigure 8.2 – Similarities of CATV with fixed/mobile terrestrial and satellite wirelessarchitecture.8-21
Chapter 8Final conclusions pTCIS streams over the DVB/DAVIC protocol. The direct consequence of having longpropagation delays is that the contention resolution algorithm interval will increasesimply because each station will have to assume longer time-out periods for thereception of a grant. In the case where a collision does not occur this will result in theCRA to be initiated with a delay equal to two times the round trip. If the traffic patternof a station is of such a nature (e.g. sporadic packet generation), this results in the use ofcontention access for the transmission of reservation requests, and performance can bedegraded significantly.8-22
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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 5Upstream channel capacity
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Chapter 6Optimisation of CRA using
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Chapter 7PERFORMANCE OPTIMISATION F
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Chapter 7Performance optimisation f
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Chapter 7Performance optimisation f
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Page 231 and 232: Referencesp[17] I. Cidon, and M. Si
Page 233 and 234: Referencesp[50] N. F. Huang, C. A.
Page 235 and 236: Referencesp[85] V. Rangel, R. Edwar
Page 237 and 238: Referencesp[112] K. Sriram, “Meth
Page 239 and 240: APPEDIX A: GLOSSARYAALABRADSLATMBCB
Page 241 and 242: Appendix AGlossary pkbpsLANLLCMACMA
Page 243 and 244: Appendix AGlossary pUSBUWVDSLVoDVoI
Page 245 and 246: Appendix BProtocol stack and packet
Page 247 and 248: Appendix BProtocol stack and packet
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Page 253 and 254: Appendix EResults for a 6 Mbps upst
Page 255: Appendix FGuide to CD-ROM p IEEE802
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