raffic of the high priority queue. The next section investigates the properties of the arrival traffic in the above system models, in order to choose appropriate arrival process models for building accurate queuing models to calculate the lub delays. 6 Dimensioning for Single ATM-Based lub 6.4.2 UMTS Iub Traffic Characteristics This section analyzes the characteristic of the carried lub traffic, i.e. the arrival traffic of the above system models, in terms of its variation and burstiness, considering different traffic scenarios. 6.4.2.1 Squared Coefficient of Variation The Squared Coefficient of Variation (COV2) represents the burstiness of the traffic. The of a constant distribution is 0 and the COV2 of an exponential distribution is 1. If COV2 >1, the traffic is considered as bursty. Figure 6.44 and Figure 6.45 show the measured COV2 for the packet interarrival time of voice and packet-switched traffic from the simulations. The results in the two figures can be summarized as follows: (1) COV2 for voice traffic varies between 1.2 and 1.8, with or without packet-switched traffic. (2) COV2 for packet-switched traffic with BRA varies between 11 and 12. (3) COV2 is different for different packet-switched RAB types. COV2 is also different for different traffic mixes. In general, higher RAB rate has a higher COV2 value. When mixing with voice, the COV² of packet-switched traffic is larger than that without mixing with voice. Therefore from the above investigations, it can be concluded that regardless of circuit- switched voice or packet-switched traffic, the arrival traffic is considered as bursty traffic as their COV²>1. Variation of RT Voice Traffic Voice ONLY BRA+10% Voice BRA+50% Voice RAB384 PS+50% voice Voice Traffic Demand [kbps] Figure 6.44: Squared CoV of packet interarrival time for RT voice traffic 6.4 Dimensioning for Transport Network Performance Variation of NRT Traffic BRA ONLY BRA+10% Voice BRA+50% Voice Packet-switched Traffic Demand [kbps] Figure 6.45: Squared CoV of packet interarrival time for NRT 