CDMA can be found in [1]. Support for a variety of mobile equipment: Rel-4 network architecture supports a variety of handheld devices ranging from voice (circuit-switched) only handsets to multimedia terminals and data air-cards (for laptops), and SO on. Improved Speech Support in CS Domain: Rel-4 features enhanced speech support, for example with Transcoder-Free Operation and Tandem Free Operation. 2 These enhancements provide transmission efficiency and cost reduction in the core network and are applicable to both GSM and UMTS systems. 3.2.3 Key Aspects of Rel-5 The two key features of Rel-5 are IMS (IP Multimedia Subsystem) and HSDPA (High Speed Downlink Packet Access). The details of Rel-5 can be found in [4] while some brief information is as follows: New Radio HSDPA: In Rel-5, techniques like adaptive modulation and coding, hybrid ARQ (automatic repeat request), and SO on, help in facilitating HSDPA [1]. It supports a peak data rate of 14.4 Mbps and 384 kbps in downlink and uplink respectively. Support for IMS: Rel-5 supports a special core network subsystem, which is called the IMS [1]. The IMS is an open signaling system, based on standard Internet technology, which supports the migration of Internet applications (like VoIP, video conferencing, messaging, etc.) to the mobile environment and offers enhanced service control capabilities. All IMS entities are located in the Core Network. These entities and procedures are used to support real-time and multimedia IP applications using Session Initiation Protocol (SIP). GERAN Iu-ps Interface: Rel-5 introduces the Iu-ps interface for GERAN, which allows GERAN to connect directly to the UMTS packet core network. IP Transport in UTRAN: In Release 99 and Release 4, only ATM (Asynchronous Transport Mode) can be used at the transport layer in the various interfaces. Rel-5 enables the usage of IP technology as an alternative to ATM technology for the transport of signaling and user data over Iu, Iur, and lub interfaces in the UTRAN. IP transport provides a cost effec