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Chapter 8Final conclusions pThe optimisation of the number of contention slots carried out in Sections 6.2.2.1 and6.2.2.2 for the exponential backoff algorithm and the splitting tree algorithm,respectively, showed that a simple contention slots allocator can increase performanceby up to ≈ 10% (Figure 6.2 and Figure 6.5). This mechanism can be directlyimplemented by manufacturers by slightly modifying the DVB/DAVIC MAC protocol.The only parameter that is needed for the operation of the Simple-CSA is the ‘Min. o.of CSs per signalling frame’ , which was not defined by the DVB/DAVIC standard.This parameter can be added to the set of operational parameters of the INA and thenmodified via the device manager, either by the manufacturer or by the operator. Resultspresented in Section 6.2.2.1 can be used as a guidance of how to set the correct numberof contention slots (for optimum performance).Similarly, the Forced-CSA can also be implemented by the manufacturer by simpleadding the parameter forced contention slots (FSc), which represents the number ofslots added to the signalling frame after a collision occurred. This scheme was the bestcontention slot allocator, because it dynamically adjusts the number of contention slotsneeded to resolve collisions according to the traffic load, and achieves an increase in theoverall system performance by up to 3% more than the figure reported by the Simple-CSA. We recommend setting this parameter to 2 for optimum system performance.The optimisation of the two contention resolution algorithms used by the DVB/DAVICprotocol (approached in Section 6.3) does not require the intervention of themanufacturer. For the exponential backoff algorithm we recommend to the operator touse the backoff windows of Bw[4-6] and Bw[4-8], which performs well for Internet andVoIP traffic. For the splitting tree algorithm the Entry spreading factor should be set to6 for best system performance.From results presented in Section 6.3.3, we recommend that cable network operatorsbuy EuroModems that support the splitting tree algorithm. In this Section 6.3.3 it wasshown that this algorithm always performs better than the exponential backoffalgorithm, regardless of the traffic load and number of active stations. AlthoughEuroModems with this functionality tend to be more expensive than EuroModemssupporting only the exponential backoff algorithm, this extra cost is compensated for by8-16