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Chapter 7PERFORMANCE OPTIMISATION FORTHE SUPPORT OF TCIS AND APERFORMANCE COMPARISON OFDVB/DAVIC AND DOCSIS7.1 IntroductionThe DVB/DAVIC protocol specification supports only a limited reservation accessmechanism (referred to as ‘pure reservation access’ - PRA) and has not yet beenoptimised for the delivery of isochronous streams. The functionality of the PRA waspreviously touched on under the CRGC, introduced in Section 3.5.1.Some contention resolution algorithms, such as the exponential backoff algorithm,produce relatively high access delays for upstream transmissions. The splitting treealgorithm, which uses less contention slots and shortened reservation requests, rapidlyresolves the contention resolution cycle, thus reducing access delays and improvingsystem throughput. However, the splitting tree algorithm combined with optimisedconfiguration parameters as discussed in Chapters 5 and 6 is not ideal for the support ofthe next generation timing critical interactive services.Therefore, in this chapter some novel improvements and techniques are introduced,which will enable the DVB/DAVIC MAC protocol to provide the delay requirementsoptimally for the delivery of delay sensitive services. The objective is to achieve anincreased performance by introducing new reservation request techniques that reduce oravoid the increased risk of collisions during congestion periods.A second approach involves QoS with a guaranteed delivery. Although, this techniqueis only supported by the second version of EuroModems.7-1