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Chapter 8Final conclusions poptimum system performance the Es factor should be set to 6 for mixed traffic (ormedium size networks) and 6 or 7 for VoIP traffic (or large networks). In terms ofsystem throughput, the difference of using distinct Es values was much less significant.It was found that the maximum system throughput ranged between ≈ 54.5% to 55% formixed traffic and from 44.8% to 45.2% of the cc for VoIP traffic.The last analysis presented in Chapter 6 approached a performance comparison betweenboth CSAs. In this analysis it was concluded that the splitting tree algorithmoutperforms the exponential backoff algorithm. This is because the former usesfeedback and allocation information that allows a station, with new incoming arrivals, tocompete for contention slots without the risk of collision with backlogged stations. Themost important advantage is that the use of minislots for reservation requests furtherdecreases the risk of collisions, since one contention-based slot is divided into threeminislots, increasing the probability of successful request transmissions. The majordrawbacks of this algorithm are higher complexity at the headend, increased processingtimes of the feedback and allocation information at the station, and since everycontention slot should be acknowledged regardless of whether it is used or not, highercontrol information at the downstream channel is assigned. In general, simulationresults showed that an increase over 9% on system performance, could be achieved withthe splitting tree algorithm when the backoff values (initial/truncated) and the Entryspreading factor have been optimised, for different traffic configurations (such as:Internet, VoIP and mixed traffic).In Chapter 7 several novel improvements were implemented. They enable theDVB/DAVIC MAC protocol to provide the delay requirements and an increasedefficiency for the support of timing critical interactive services and high-speed datatransmissions. The first analysis focused on the performance increase achieved by theuse of six enhanced-reservation-request mechanisms (Reserved Request, ContinuousReserved Request, Enhanced-Pure Reservation Access, Piggyback Request, ContinuousPiggyback Request and Unsolicited Grant Slot).The introduction of these techniques was because the DVB/DAVIC protocol uses alimited reservation access mechanism (PRA) by default for the transmission of8-11