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Chapter 5Upstream channel capacity and characterisation pA recommendation can now be made for CATV networks based on the DVB/DAVICprotocol. The maximum request size should be set as large as possible if the upstreamchannel is only used for Internet traffic. A value of 32 ATM cells for this parameter wasfound to provide the best system performance. However, if the upstream channelsupports the transmission of both traffic sources (IP and VoIP), a higher interaction forVoIP streams can be obtained if the maximum request size is set as short as possible.Here a value of 6 ATM cells for this parameter was found to provide the fastestinteraction for VoIP traffic.5.4.5 Effects of buffer capacityIn most CATV networks, there are circumstances in which the externally offered load islarger than can be handled even with optimal transmissions. In these cases, if nomeasures are taken to restrict the entrance of traffic into the network, queue sizes at astation’s buffer will grow and packet delays will increase, possibly violating maximumdelay specifications. Furthermore, as queue sizes grow indefinitely, the buffer space atsome stations may be exhausted. When this happens, some packets arriving at thesestations will have to be discarded and later retransmitted, thereby wastingcommunication resources.This analysis examines to what extent traffic congestion of CATV networks can becontrolled by restricting the station buffer capacity in order to provide considerable lowdelays for the support of bursty applications (e.g. Internet traffic) and isochronousinteractive services (e.g. Voice over IP traffic, audio and video). For this analysis, amixed traffic configuration was chosen. The mean data rate per active station was set to41.7 kbps, which consisted of 32 kbps Internet traffic and 9.7 kbps VoIP traffic, asintroduced in Section 5.3.3. In order to demonstrate the effect of the buffer capacity, sixdifferent bounds were analysed (50, 100, 300, 500, 1000 and 3000 ATM cells). Thesimulations were performed using only the splitting tree algorithm.5-23
Chapter 5Upstream channel capacity and characterisation pIt can be noticed in Figure 5.13 that the access delays increase as the maximum buffercapacity builds up. The results shown in this figure indicate that the maximum numberof VoIP streams supported is 40 (which produce 54% of the link capacity), with meanaccess delays below 50 ms, regardless of the buffer size. On the other hand, bufferlimits holding up to 100 ATM cells (38 Kbits of data) yield acceptable access delays(under 1 second) for the transmission of Internet traffic, with an offered load up to ≈67% of the channel capacity, supporting up to 50 IP streams.Mean Access Delay (s)1010.10.01Buffer-50-ATM cellsBuffer-100-ATM cellsBuffer-300-ATM cellsBuffer-500-ATM cellsBuffer-1000-ATM cellsBuffer-3000-ATM cells3 Mbps Upstream32 Kbps kbps IP &9.7 Kbps kbps VoIPTree Algorithm28 30 32 34 36 38 40 42 44 46 48 50umber of Active StationsFigure 5.13 – Mean access delay vs. No. of active stations for increased buffer size.5-24
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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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