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Chapter 4Simulation and analytical modelling pWe have proved that simulated performance of the system does not depend on the seedused, therefore it will not be mentioned again and all simulation results presented in thefollowing chapters will be yielded using a seed of 257.For a larger number of nodes, we also carried out a rigorous verification test of theoperation of the DVB/DAVIC simulation model. For this test, we used a mixed trafficpattern consisting of 32 kbps IP traffic and 9.7 kbps VoIP traffic (these traffic types aredescribed in Section 5.4), using the exponential backoff algorithm. We ran a simulationfor 60 seconds and captured the sequence of events between the 59 th and the 60 thsecond. Appendix D shows this sequence for 30 stations. From analysing these eventswe can verify that every station transmitted all packets received and used the contentionresolution algorithm correctly. On average, every station received (1/(0.092 IP interarrival+ 0.12 VoIP inter-arrival) = 19.6 packets per seconds, which corresponds to thenumber of packets received and transmitted in Appendix D.4.6 ConclusionsThe DVB/DAVIC protocol is a relatively new specification and little information aboutits performance and scalability is known. In this chapter, the suitable simulation andtheoretical models have been presented. These models will be used in subsequentchapters for the performance evaluation, optimisations and enhancements of theDVB/DAVIC protocol.The simulation model implemented for this research was based on the main networktopology of the CSF (v.13), developed by MIL3, Cablelabs and the University ofSheffield. This model has been significantly modified to support the basic functionalityof the MAC and PHY layers of the DVB/DVIC protocol, including the functionality ofthe two contention resolution algorithms adopted by the DVB/DAVIC protocol. Inaddition, new features for further optimisations were also incorporated in the simulationmodel, such as contention slot allocators, enhanced reservation requests mechanisms,and a prioritised scheduler, which will be used in subsequent chapters.Existing analytical models from the literature were insufficient to model theDVB/DAVIC protocol, as they did not take into account the variable bandwidth of the4-35