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Chapter 7Performance optimisation for the support of TCIS pup to 4096. This results in MAP being transmitted from ≈ 1ms when only contentionminislots are described up to (4096minislot·128bits/2560000≈) 200 ms on high trafficloads.Figure 7.22b shows an increased system performance for DOCSIS over theDVB/DAVIC protocol in terms of system throughput and utilisation, even though areduced upstream channel capacity was used for the DOCSIS protocol. For thisanalysis, the maximum system throughput resulted in ≈ 65% of the channel capacity forthe DVB/DAVIC protocol, in comparison to 90% of the cc achieved by the DOCSISprotocol.In terms of utilisation, the DVB/DAVIC protocol uses 89% of the channel capacity incomparison to 93% utilised by the DOCSIS protocol. Both protocols cannot achieve100% of the upstream channel capacity due to slots assigned to the contention accessregion that remained unused. Reducing the minimum number of contention slots perMAP or signalling frame may result in an increase of upstream channel utilisation, butthere may be also some drawbacks, such as an increased number of collisions in periodsof congestion and therefore an increased mean access delay.D) Effects of packet size in isochronous streamsHere, an analysis of the performance impact in terms of mean access delay is presented.The system throughput provided by each protocol when the packet size is ranged from64 to 1518 bytes for different isochronous streams is shown. For this analysis, streamsfrom 16 kbps to 128 kbps, suitable for low-rate timing critical interactive services suchas compressed/ uncompressed voice, audio and low quality video were considered.7-33