 Node B and the RNC support both HSPA and Rel99 services. In this approach, there are two traffic paths: one for HSPA path and the other for Rel99 path. The HSPA path is realized by using the existing HSPA simulation model, which is introduced in section 5.6. The Rel99 path is however using the traces generated from the separate Rel99 simulations for both uplink and downlink, instead of using the developed Rel99 simulation model directly in the scenario. The main reason for not using the implemented Rel99 simulation model is due to that the Rel99 and HSPA simulation models were developed separately in different NSN research projects and they cannot run in the same simulation scenario. However using the trace data for the Rel99 traffic does not cause significant inaccuracy of the results, because in most of cases Rel99 traffic has a higher priority to transmit than HSPA traffic and thus the characteristics of the Rel99 traffic is not influenced by the generated HSPA traffic. One benefit of using this approach is its simulation efficiency. Because the Rel99 path uses only the traces generated from the separate simulations, it reduces the complexity of the combined simulation model as well as decrease the overall simulation run time. Node B HSUPA HSPA UEs Node B HSDPA module moudle ATM UBR VC/VPs Switch lub ATM Links Switch Rel99 Node B Rel99 RNC module ATM CBR VC/VP module Rel99 UL Rel99 UL traffic Rel99 UL traffic sink source Rel99 DL Rel99 DL Rel99 DL traffic traffic sink source Figure 5.7: Modeling of combined UMTS Rel99 and HSPA 5 Introduction of Simulation Models As shown in Figure 5.7, the model of the Node B is composed of the HSPA Node B module from the existing HSPA simulation model, and the Rel99 Node B module including an uplink (UL) traffic source and Rel99 downlink (DL) traffic sink. The model of the RNC is composed of the HSPA RNC module from the existing HSPA simulation model, and the Rel99 RNC module including a DL traffic source and UL traffic sink. The HSPA traffic and Re199 traffic are carried by