a from the AAL layer; decapsulates and forwards data to the AAL layer; forwards cells from the ATM Management module. The AAL module implements the encapsulation and decapsulation of SAR_PDUs following the AAL1, AAL2, AAL3/4 and AAL5 protocol, and also creates and invokes signaling and connection processes to handle new connections, incoming signals and data. The ATM_call_control module accesses interfaces between the data plane and the control plane. The ATM_sig module handles signaling to establish and release an ATM connection The ATM Switch module switches cells to output ports. It also implements buffer management, based on QoS and the ABR feedback mechanism. The ATM Translation module receives incoming ATM cells from network; translates VPI/VCI values for outgoing cells; forwards cells to appropriate ATM module. The ATM server model is usually used together with the ATM workstation. The server can support all of the application models. Appendix A.9 Introduction for HSPA (HSUPA/HSDPA) As mentioned in chapter 2, the evolution of the mobile communication market brings demands for both larger system capacity and higher data rates. To boost the support for the packet switched services, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) are introduced by the 3GPP Release 5 and 6 respectively as the evolution of UMTS which strongly enhance the transmission of data packet traffic on the downlink and uplink separately. They are jointly referred to as High-Speed Packet Access (HSPA). Following gives a detailed introduction of HSDPA and HSUPA protocol architectures, the impact of HSPA on the UTRAN lub interface, and specific traffic control functions to be employed in the UTRAN for HSPA. HSDPA and HSUPA User Plane Protocol Architecture HSDPA and HSUPA are the extensions of the UMTS Rel99 network, SO their basic protocol layers are similar to the Rel99 system. But both introduce new protocol entities in the architecture to support the enhanced features such as fast scheduling, fast HA