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Chapter 5Upstream channel capacity and characterisation pof the maximum length of a message (measured in ATM cells) that can be transmittedusing either contention access or a single reservation request; buffer capacity; scalabilityof the upstream channel in terms of increased offered load and node population.The major factors affecting the system performance were seen to be the length of thepacket being transmitted for delivery. Specifically it was demonstrated that regardless ofthe offered load and length of the packet size, a single station cannot achieve throughputhigher than 32% of the maximum upstream channel capacity, even when the splittingtree algorithm is used. However, this figure can be as low as 1.8% when deliveringminimum Ethernet packets (64 bytes) due to an excessive number of reservationrequests, collisions, retransmissions and DVB MAC and PHY protocol overheads.Results for channel utilisation were higher than for throughput results with a range of54% to 23% for minimum and maximum Ethernet packets, respectively. Protocoloverhead was shown to be a major source of performance inefficiency. This can be ashigh as 35% of the upstream channel capacity for 64-byte packets.Effects of contention access for data transmission revealed that by transmittingrelatively short messages (in the order of 1-ATM cell) using only contention access, thesystem throughput can be increased and a quick interaction can be provided. Results foreffects of reservation request size suggested that the maximum request size should be setas large as possible if the upstream channel is only used for Internet traffic. However, ifthe upstream channel supports the transmission of both traffic types (IP and VoIP), ahigher interaction for VoIP packet can be obtained if the maximum request size is set asshort as possible.Results for the buffer capacity indicated that traffic congestion could be controlled bylowering the incoming traffic to the CATV network. Thus, there is a natural trade-offbetween giving sessions free access to the network and keeping delay at a level lowenough so that interactive applications (e.g. VoIP, audio and Video) are supported andretransmission or other inefficiencies do not degrade the network performance.Scalability of the upstream channel revealed that there is a gradual increase in theperformance of the system with respect to increasing the cable population and offeredload. Results also revealed that there are distinct saturation points after which5-37
Chapter 5Upstream channel capacity and characterisation pthroughput and utilisation do not increase, meanwhile packet delays becomeunbounded. For all of these analyses, the maximum channel utilisation remained atapproximately 90% of the link capacity.Careful design should not allow a network population and offered load to exceedsaturation points, since this would result in uncontrolled access delay.Finally, given all these special characteristics of the protocol and the fact thatisochronous applications (e.g. VoIP) are very sensitive to delay variations, it isnecessary to further optimise the protocol.5-38
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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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