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Chapter 8Final conclusions pA second approach for increased performance was through the use of Quality ofService. We have found that the main drawback of using the reservation access modefor the provision of delay sensitive applications is that bandwidth cannot be guaranteed.This is because all traffic transmitted using this mode is treated with a ‘best-effort’service and in some situations the delivery of TCIS requires an especial treatment for animproved service.Therefore, in order to provide a guaranteed service for TCIS the use of QoS isfundamental. Two types of QoS were studied. They are known as prioritisation andreservation.Although traffic prioritisation is not part of the set of functionalities of theDVB/DAVIC protocol specification, we have demonstrated that a faster transmissionfor the delivery of TCIS streams can be achieved by mapping the ToS field of the IPprotocol, with at least two 2-levels of priority at the DVB/DAVIC MAC layer. This willgive a faster delay treatment to TCIS stream. Results from a mixed traffic configuration(at 41.7 kbps) revealed that after the saturation point, the prioritised mechanism stilloffers tolerable delays (about 50 ms) for TCIS streams. Here, the number of VoIPstreams was increased from ≈ 40 with the default PRA up to ≈ 50 connections with theprioritised mechanism. The major drawback of this technique is that it does not provideany guarantee of bandwidth availability or latency with high traffic loads.On the other hand, the reservation technique uses the fixed access mode of theDVB/DAVIC protocol to provide a guaranteed service. Here the number of slots neededby a station and the periodic intervals is negotiated during the connection setup. Withthis technique, we have seen that reduced packet access delays for the delivery ofisochronous streams, in the range of 1 and 2 ms could be guaranteed by theDVB/DAVIC protocol, before large periods of congestion are experienced. It was alsofound that for the same traffic configuration (at 41.7 kbps), on high traffic loads, theservice of IP traffic gets starved at the headend and the number of VoIP streams couldbe significantly increased up to 320. In order to avoid the starving service for IP traffic,the scheduler algorithm at the headend could be slightly modified to control the8-13