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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