rformance is mainly determined by the transport network of the lub interface. In this model, each Node B serves up to three cells, which is independent of each other. Each cell can establish its own channels and users. They all share the same lub link. As only the aggregated traffic of all three cells at the lub is important, there is no identification of traffic for each cell. Moreover, handover function is not specifically modeled. Because the dimensioning of the lub interface only takes into account the total amount of the traffic generated by the whole cell. For the lub dimensioning purpose, it is not necessary to distinguish whether the traffic is for the handover users or not. 5.4 Simulation Model of UMTS Rel99 Modeling of Channels Section 3.3.2 introduces the logical and transport channels in UMTS defined by the 3GPP. In this simulation model, only two types of logical channels and three types of transport channels are modeled. The modeled logical channels are Dedicated Traffic Channels (DTCH) and Dedicated Control Channels (DCCH). Each user connection has a pair of DTCH and DCCH where the DTCH is the traffic channel for transmitting the user data and DCCH is the control channel for sending the corresponding control information for this user connection. According to 3GPP 34.108 [3GP04e], a variety of RABs can be assigned to the DTCH while the DCCH only uses Signaling Radio Bearer (SRB) of 3.4 kbps. Both logical channels are normally mapped to DCH transport channel. But if the user is transmitting the data via a shared common transport channel, they will be mapped to Forward Access Channel (FACH) on the downlink and Random Access Channel (RACH) on the uplink. Each UMTS cell models one pair of RACH and FACH, the implemented data rate is 32 kbps for each. While for each DCH, a specific RAB rate is assigned depending on the user requirement and the network resource management functions. For these three transport channels, the corresponding Transmission Time Interval (TTI) and the Transport Block Set (TBS) are 