under congestion situations. This can help to improve the effective throughput by gradually reducing the burstiness. The congestion control algorithm consists of two basic functionalities: congestion detection and congestion control. These basic functionalities are applied individually per MAC-d flow and basically using information contained in the FP frame. The congestion detection function is responsible for detecting any possible congestion on the lub link. The detection can be based on frame loss, or the frame delay over the lub link [3GP06d]. Upon detection of congestions, the congestion indication is signaled to the congestion control module. The congestion control function is to adaptively reduce the MAC-d flows lub rate according to the available lub bandwidth, SO that persistent congestion situations for a MAC-d flow do not mean degraded throughput but just the adaptation of the MAC-d flow rate to the available bandwidth. In fact this action enables the upper layers to recover from congestion In HSDPA, the congestion detection and the congestion control are performed at the Node B. The result of the CC is the potential reduction of credits in the capacity allocations (CA) of the frame protocol (FP), which are issued by Node B and need to be followed by RNC. For the HSUPA network, the congestion detection is done at the serving RNC, while the congestion control is executed at the Node B. More detailed information on the congestion control algorithms for HSPA can be found in [WTG*08]. A.10 Simulation Model of HSPA A.10 Simulation Model of HSPA The HSPA is the extensions of the UMTS Rel99. In the framework of this thesis, the UTRAN network for the HSPA is based on the ATM. The following gives a brief introduction of the existing HSPA simulation model, which contains the modeling of HSDPA for the downlink and HSUPA for the uplink separately. I. Modeling of HSDPA In the HSPA simulation model, the main features, protocol stacks and specific lub traffic control functions of the HSDPA were modeled detailed accor