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Chapter 7Performance optimisation for the support of TCIS papproximately 50 ms, which is suitable for the support of audio streams with heavytraffic loads. Delays for Internet traffic were lower with the PG mechanism due to thecontinuous piggyback requests on high traffic loads, which avoids contention access.In terms of system throughput, when prioritisation is not used (see Figure 7.13a), wecan observe that the throughput for both traffic types increases almost linearly withrespect to the NIUs population up to the point of saturation (reported at 57% of the cc,with 42 stations) . After this, VoIP and Internet packets start accumulating in the NIU’squeues. Conversely, with prioritisation (Figure 7.13b), it can be seen that bothreservation request mechanisms transmit all VoIP streams in the first place and then useremaining bandwidth for Internet packets. As explained in Section 7.2.7, the PGmechanism achieves a higher system throughput than the PRA because of the reducednumber of collisions in periods of congestion.With very high traffic periods (above 73% of the cc or 54 stations), there is a slightdifference for VoIP traffic. With the PG mechanism after transmitting the VoIP streamssome piggybacks requests are made for Internet traffic. These requests at the headenddelay subsequent piggyback requests made for VoIP traffic. This is because the headendgrants all requests using a best-effort service. This problem can be solved by replacingSystem Throughput (%)50454035302520151050a) Without Prioritisation - PRA b) With Prioritisation - PRA & PGInternetTrafficVoIPTraffic34 36 38 40 42 44 46 48 50 52 54umber of Active StationsInternetTrafficVoIPTrafficPRAPGPGPRA34 36 38 40 42 44 46 48 50 52 54 56 58umbe r of Active StationsFigure 7.13 – System throughput vs. No. of active stations for VoIP and Internet traffic.Splitting tree algorithm with and without prioritisation.7-16
Chapter 7Performance optimisation for the support of TCIS pthe scheduling mechanism at the headend with one that supports at least two levels ofpiggyback or even reservation requests and also gives higher priority to VoIP traffic orTCIS applications in general.Although this prioritisation mechanism offers an improved performance for TCISapplications, a more efficient mechanism is examined in the following section.7.3.2 Reservation (Fixed-rate access) in QoSThe second approach for QoS with a guaranteed service, uses a fixed-rate accessconnection. In such connections data is sent in slots assigned at a fixed-rate basedaccess region in the upstream channel, as described in Section 3.5.4, Figure 3.6. Theseslots are uniquely assigned to a connection by the INA. The number of slots needed by aconnection and the periodic intervals are negotiated during the connection setup. Thecomplete set of procedures is illustrated in Figure 7.14.When an NIU requires a new fixed-rate connection or needs to change fixed-rateparameters, a Resource Request message is first sent to the INA by the NIU, includingthe new parameters. Example parameters are new cyclic assignment needed, requestedbandwidth, distance between slots and connection identifier (CID). The INA answerssuch requests by sending a Connect message to the NIU, indicating whether the newcyclic assignment is granted and if so, a new set of fixed-rate parameters are providedsuch as frame length, fixedrate start, fixedrate distance, fixedrate end and CID.Connection-SetupINA / HeadendResource RequestConnect MessageConnect ResponseNIU / EuroModemNew cyclic assignment needed(requested bandwidth, maximumdistance between slots and CID)Cyclic assignment granted(CID, frame length, fixedrate start,fixedrate distance and fixedrate end)CIDConnect ConfirmFigure 7.14 – Connection-setup for a Fixed-rate access connection.CID7-17
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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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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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