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Figurę 4: Basic architecture of a UMTS mobile network (Release 99) (from [11]).

be reached. Figurę 5 shows the most recent proposal for the organization of a UMTS network: the all-IP multimedia network architecture defined in Release 5. The main feature of this architecture is that both voice and data are carried over IP packets all the way from the mobile station to finał destination, thanks to the addition of a new domain in the core network: the IP-Multimedia domain (IM).

The next is a brief description of the UTRAN components:

User Eąuipment/Mobile Station (UE/MS): Is the physical device used by users. It consists of a Mobile Eąuipment (ME) and an UMTS Subscriber Identity Module (USIM). The USIM is an application stored in a removable IC card which interoperates with the ME to provide access to 3G services and has the following features:

i Unambiguously identifies a subscriber i Stores subscriber and subscription related information i Authenticates itself to the network and vice versa (mutual authentication) i Provides security functions

i Stores information elements such as: preferred language, IC card identification, International Mobile Subscriber Identity (IMSI), cipher key, among others

Node B: Is the base transceiver station of the UTRAN that serves one or morę cells (sectors). Some of its functions include: error detection on transport channels and indication to higher layers, modulation/demodulation of physical channels, radio measurements and notification to higher layers and power weighting. Some vendors offer base stations that support both UMTS and CDMA2000 standards through the use of field-replaceable modules and a high percent of compatible hardware and software. The interface between UE and Node B (Uu in figurę 4) is actually the WCDMA-based UTRĄ radio interface.