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Chapter 7Performance optimisation for the support of TCIS pFor mixed traffic on loads of under 46% of the cc (34 stations), the CPG mechanismalso provided the lowest access delays. However, for the transmission of VoIP streamson loads of under 33% cc (105 stations), it did not offer the lowest access delaysbecause it was seen that with a large number of active stations, the headend has to granttwo types of requests. These are the requests made for one slot, which are then used tosend a further reservation request and the requests made for the transmission of datamessages. In simulation, it was seen that for low traffic loads, most requests are madefor one slot, which delay the other requests for data messages. Thus, the NIUs have towait longer in order to transmit their data slots.A similar effect is also appreciated with CRR. However, in this case the number ofrequests made for one slot is larger than with the CPG mechanism. This is because thereservation requests are made for the transmission of the current data packet, and theCPG not only requests bandwidth for the current data message but also for other packetsin the queue, as long as the number of slots requested does not exceed the maximumpiggybackedrequest threshold (set to 12 slots). Hence, mean access delays are slightlylarger than those produced by the CPG and the other mechanisms.In terms of number of VoIP streams supported, with the PRA and PG mechanisms only105 connections can be upheld with mean access delays of under 50 ms. That numbercan be increased to 110 connections with the use of the RR and EPRA mechanisms.However, with the CPG mechanism the network capacity can be extended up to 124connections.Results for mixed traffic indicate that the number of VoIP streams supported in thepresence of Internet traffic is 32 connections with the PRA mechanism. Simulationshave also shown that this number can be extended by up to 8 connections using theenhanced-reservation-request mechanisms.7-9