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Chapter 7Performance optimisation for the support of TCIS pB) Performance analysis for the splitting tree algorithmSimulations with the splitting tree algorithm, Figure 7.10a indicates that for pure VoIPtraffic optimum system performance may be obtained using the unsolicited grantmechanism. With this mechanism the network capacity is considerably increased to thehighest figure for this research at ≈ 170 connections. This equates to approximately 53%of the available channel capacity and produces mean access delays below 7 ms. Hence,this mechanism has been shown to match the requirements of CBR. The othermechanisms, with the exception of CPG, support the same number of connections equalto ≈ 145.Results for mixed traffic are shown in Figure 7.10b. It should be noted that discussionof the UGS mechanism is absent here since in a mixed traffic situation the constant bitrate requirements cannot be satisfied using this technique. From the figure we can alsoappreciate that the enhanced-reservation-request mechanisms are more effective withhigh traffic loads. For example, for traffic loads above 55% of the cc, the maximumnumber of Internet connections that can be supported was ≈ 45 with the CPGmechanism, compared with ≈ 41 with the PRA mechanism. For delay sensitiveapplications the number of connections supported resulted in ≈ 40, regardless of themechanism utilised.Mean Access Delay (ms)30027525022520017515012510075502503 Mbps Uptream9.6 9.7 Kbps kbps VoIPSpliting Splitting Tree CRAa) VoIP Traffic b) Mixed TrafficCPGEPRAPRA70 80 90 100 110 120 130 140 150 160 170umber of Active StationsPGUGS7-123 Mbps UpteamMixed TrafficSplitting Spliting Tree CRAPRAEPRACPG37 38 39 40 41 42 43 44 45 46 47umber of Active StationsFigure 7.10 – Bandwidth consumed by collisions vs. No. of active stations for VoIP andmixed traffic. Splitting tree algorithm with enhanced-reservation-request mechanisms.PG
Chapter 7Performance optimisation for the support of TCIS pIn general, the UGS and also the CPG (for small networks) are quite efficient and bestsuited for the delivery of VoIP streams. For Internet traffic, it was found that the CPG,PG and EPRA mechanisms, combined with the use of the splitting tree algorithm, aremore appropriate for the transmission of Internet and bursty traffic.With all of the enhanced-reservation-request mechanisms, it has been demonstrated thatthe number of VoIP streams and Internet connections can be significantly extended,using only the reservation access mode of the DVB/DAVIC communications protocol.This access scheme is the basic mode for the first version of EuroModems [36]).A drawback of using the reservation access mode for the provision of delay sensitiveapplications is that bandwidth cannot be guaranteed. This disadvantage is because alltraffic transmitted using this mode is treated with a ‘best-effort’ service and in somesituations, the delivery of TCIS requires a special treatment for an improved service.Therefore, in order to provide guaranteed bandwidth for TCIS, the use of QoS is crucialand is addressed in the following section.7.3 Quality of Service (QoS)This section outlines some issues related to QoS and how a cable network compliant tothe DVD/DAVIC protocol specification can make use of QoS characteristics for theprovision of guaranteed bandwidth. Here a comprehensive performance analysis forQoS is presented for the support of TCIS.In the simplest sense according to [82], QoS is the ability of a network element (e.g. anapplication, host or router) to have some level of assurance that service requirementscan be satisfied, providing a consistent predictable data delivery service.The Internet Protocol provides what is called a ‘best-effort’ service, making noguarantees about when data will arrive, or how much traffic can be delivered. Timingcritical interactive applications, including voice, audio and video streaming, demandhigh data throughput with low-latency in two-way communications.7-13
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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 4Simulation and analytical
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Chapter 5Upstream channel capacity
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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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