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Chapter 8Final conclusions pslots into the signalling frames. Here it is most likely that unscheduled slots are assignedto contention access).In an analysis for the IEEE 802 protocol (reported in [94] and [96]) it was pointed outthat the performance of multi-access reservation protocols heavily depends on theoverall structure and the capacity assigned to the reservation and contention accessregions. Therefore, in this chapter we have demonstrated that the performance of theDVB/DAVIC can be improved if these techniques are used.The first strategy studied was the Simple-CSA. Here the minimum number of contentionslots per signalling frame was ranged from 1 to 7 using the exponential backoffalgorithm and from 0 to 6 using the splitting tree algorithm. When the exponentialbackoff algorithm was used it was found that by allocating at least 3 or 4 CSs persignalling frame, not only lower access delays were yielded but also an increase insystem throughput was achieved. Larger values (e.g. 5, 6 and 7 CSs) caused a waste ofbandwidth because more CSs are allocated than the number of CSs required to resolvecollisions. Similarly, a low system performance is also obtained when short values (e.g.1 and 2 CSs) are considered. Here the system inefficiency is attributed to an increasednumber of collisions, due to a reduction of slots for contention access. Results for thesplitting tree algorithm revealed that optimal system performance is achieved byallocating at least 1 CS per signalling frame. The increase in performance is achievedbecause an extra slot is reserved in the next signalling frame when a collision happens.This extra slot (is split into three minislots that carry shortened reservation requests) andis used only by the stations that caused the collision, so that new arrivals do not competewith backlogged stations for contention access. The increase in system throughput isachieved because by allocating at lest 1 CSs in each signalling frame, more slots can bescheduled for data transmissions.8-8