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Chapter 7Performance optimisation for the support of TCIS pb) G.723.1 PerformanceResults for the codec G.723.1 (presented in Figure 7.17a) show that by using a framesize of 30 ms, up to 160 stations can be sustained at 59% of the cc. This number can beextended to 320 VoIP connections with header suppression, but a reduction in terms ofsystem throughput is obtained, achieving about 39% of the channel capacity. This loss(of about 20% of the cc) is caused by the 12 bytes padding used to encapsulate the 28-byte audio packet to fit into one (48-byte) AAL5 PDU (as indicated above). The otherthree Voice packet configurations do not suffer this large reduction, because they fitproperly into a fixed number of ALL5-PDUs.With codec G.723.1, optimum system performance is obtained when header suppressionis considered and a frame size of 120 ms is used. The network capacity increases to thehighest figure for this research supporting up to approximately 640 VoIP connectionsand producing a mean access delay below 2 ms before congestion is experienced(Figure 7.17a). This equates to 60% of the available channel capacity (Figure 7.17b).The results presented in this subsection for both audio codecs can be validated by usingEquations 7.1 and 7.2, for the maximum system throughput sustainable and themaximum number of streams supported, respectively.Mean Access Delay (ms)109876543210a) G.723.1: Mean Access DelayFs-30msFs-120ms+HSFs-120msFs-30ms+HS0 100 200 300 400 500 600 700umber of Active StationsSystem Throughput (%)636057545148454239363330b) G.723.1: System ThroughputFs-120ms+HSFs-120msFs-30ms+HSFs-30ms30 35 40 45 50 55 60 65Offered Load (%)Figure 7.17 – Mean access delay and system throughput.Splitting tree algorithm and VoIP traffic (G.723.1 at 5.3 kbps).7-23