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Chapter 7Performance optimisation for the support of TCIS pThe frame length parameter indicates the number of successive slots to use in the fixedrate access region associated with each fixed rate slot assignment. The fixedrate startparameter indicates the starting slot within the fixed rate access region that is assignedto the NIU. The NIU may use the next frame length slots of the fixed rate accessregions. The fixedrate distance parameter represents the distance between additionalslots assigned to the NIU and the fixedrate end parameter indicates the last slot that maybe used for fixed rate access.Subsequently, the NIU accepts the connection by sending a Connect Response message(indicating its CID) to the INA, which in turn answers this message by sending aConnect Confirmation message to the NIU.The analysis to follow will address the optimal system performance of the DVB/DAVICcable communications protocol when QoS (with a guaranteed service) is supported.Two traffic types were analysed: mixed traffic and VoIP traffic. For this analysis theoptimised simulation parameters presented in Table 7.1 were used with the followingexceptions:• The upstream data rate of 3.088 Mbps was changed for an upstream channel with acapacity of 6.176 Mbps. This change was considered necessary because the resultspresented in the previous sections and also in the previous two chapters were basedon a 3.088 Mbps upstream channel. The DVB/DAVIC protocol is also capable ofsupporting a 6.176 Mbps in the upstream direction. Therefore, in order to approachthe maximum system performance in terms of the maximum number of activestations supported, an upstream channel with a capacity of 6.176 Mbps was used.• The number of signalling frames transmitted in the 3 ms period was changed to 4,instead of 1. This is because stations can achieve a faster interaction (as examined inSection 5.4.6) with the headend, if more than one signalling frame is transmittedwithin the 3 ms period, which results more convenient for the support of TCIS.• The minimum number of CSs allocated per signalling frame was changed to one,instead of two. In Section 6.2.2.2, it was proved that the maximum system7-18
Chapter 7Performance optimisation for the support of TCIS pperformance is yielded with at least one CS per signalling frame when the splittingtree algorithm is used.• The maximum number of active stations analysed was up to 680 instead of 180 inorder to cover the point when saturation is experienced and very low-data ratestreams are delivered.A) Performance analysis for mixed trafficIn this section, a performance comparison is provided when the PRA and QoS (with afixed-rate connection) mechanisms are used for the transmission of mixed traffic. Thesimulations were carried out using only the splitting tree algorithm and the mixed trafficconsisted of 9.7 kbps of VoIP traffic and 32 kbps of Internet traffic, as described inSection 5.3.3.It can be seen in Figure 7.15a that the delay characteristics for both traffic types weresimilar for the PRA mechanism, which supports approximately 80 stations. On the otherhand, with QoS not only an extended number of VoIP connections can be supported (upto 320), but also the mean access delay is reduced and ranged between ≈ 1 or 2 msbefore the system becomes unstable.This reduction in access was because the number of MCI frames transmitted in the 3msperiod was increased to 4 and this helped the NIUs to achieve a faster interaction withthe INA, and also because VoIP traffic had precedence over IP traffic at the headend.a) Mixed Traffic: Mean Access DelayMean Access Delay (ms)50454035302520151050Internet & VoIPTrafficPRAInternet TrafficQoS-FxdrateVoIP Traffic40 80 120 160 200 240 280 320b) Mixed Traffic: System ThroughputSystem Throughput (%)5550454035302520151050Internet TrafficPRAPRAQoS-FxdrateVoIP TrafficQoS-Fxdrate40 80 120 160 200 240 280 320umber of Active Stationsumber of Active Stations7-19Figure 7.15 – Mean access delay and system throughput vs. No. of active stations.Splitting tree algorithm with mixed traffic.
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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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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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