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Chapter 6Optimisation of CRA using adaptive CSAs pFor Internet traffic at 64 kbps per station, the highest system throughput was achievedwith the Variable-CSA and the lowest access delay with the Forced-CSA. For theVariable-CSA two configurations were used. The maximum system throughput ofapproximately 51% at 52% of the channel capacity (generated by 25 stations) was foundby allocating at least 3 CSs per signalling frame. For this traffic type, a slight increase inthe average number of CSs needed per request (with 2.871 CSs) was registered, whichresulted in a small reduction in system performance of 0.2% in comparison with Internettraffic at 32 kbps.For a better appreciation of the performance impact when using enhanced CSAs, amixed traffic situation will be carefully analysed. For this traffic type (comprised of 32kbps Internet and 9.7 kbps VoIP traffic), the maximum theoretical bound for the systemthroughput can now be estimated by taking the mean packet size transmitted (measuredin bytes and in slots), as indicated in Equation 6.4.PkPbIP⋅ PkIP+ PbVoIP⋅ PkVoIPSmax ==(6.4)Pk + eCSs Pb ⋅ Pk + Pb ⋅ Pk eCSsslots IP slots_IP VoIP slots_VoIP+where Pk IP (=368.1) and Pk slots_IP (8.3) are the average Internet packet sizes measured inbytes and data slots respectively. Similarly, Pk VoIP (=146) and Pk slots_VoIP (=4) are theVoIP packet sizes measured in bytes and data slots respectively. Finally, Pb IP and Pb VoIPare the probability that an IP or VoIP packet will be generated, respectively. Equations6.5 and 6.6 give these probabilities.PbPbDrIPIP= (6.5)PkIPDrIP+ ⋅ DrVoIPPkVoIPDrVoIPVoIP= (6.6)PkVoIPDrVoIP+ ⋅ DrIPPkIPwhere Dr IP (= 32 kbps) and Dr VoIP (= 9.7 kbps) are the mean data rates of Internet andVoIP traffic generated per station, respectively. Therefore, the maximum theoreticalsystem throughput that can be yielded for mixed traffic is 46.4% of the channelcapacity.6-13