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Chapter 8FINAL CONCLUSIONS8.1 IntroductionThe work presented in this dissertation has addressed the issues of digitalcommunications over the European cable communication protocol (DVB/DAVIC, ETS200 800). The focus of this work has been the performance evaluation and optimisationof the upstream channel, which is more complex to analyse when compared with thedownstream channel. This is because transmission on the downstream channel ishandled exclusively by the headend (the Interactive Network Adaptor), simplifyingoperation. In contrast, the upstream channel is a shared access medium, which usesrandom (contention), reservation and fixed access techniques. The interval distributionof the start time of these access modes is dynamic and controlled by the headend. Theboundaries of contention and reservation access are broadcast periodically in thedownstream channel. The boundary of fixed rate access is assigned to a station at thebeginning of connection. When collisions occur, a contention resolution algorithm isused to resolve them. This protocol uses two different CRAs, which are the exponentialbackoff algorithm and the splitting tree algorithm.The series of analyses presented in this dissertation have concentrated on theeffectiveness of the access modes and the CRAs defined in the DVB/DAVIC protocolspecification with the key performance issues for access and data transmission in theupstream channel. In addition, several improvements have also been introduced toextend this protocol in support of high-speed data transmissions and in particular timingcritical interactive services.8-1