Toward an all-IP-based UMTS system architecture
Looking into the future, two main drivers for the mobile telecommunications market can be identified: third-generation mobile systems (e.g., UMTS) and the Internet (e.g., the introduction of IP technologies like voice/multimedia over IP in mobile networks). UMTS is seen as the enabler of wireless multimedia applications and portability of a personalized service set across network/terminal boundaries, as defined within the virtual home environment (VHE) system concept. In light of these recent
... olutions, this article investigates the impact of the evolution toward an all-IP UMTS network architecture on the UMTS service architecture, which is based on the VHE concept. The article discusses two possible scenarios for supporting VoIP services in the UMTS service architecture and analyzes their applicability in an all-IP-based UMTS network. The first is based on the traditional centralized IN service architecture. The second proposes a new decentralized architecture based on direct control of VoIP call control equipment by open service architecture interfaces. B B IEEE Network • January/February 2001 37 heavily contributed to the immense level of success in industry of the all-IP UMTS network architecture. The second trend  was the evolution toward an open service architecture (OSA) which obliged network operators to provide third party service providers access to their UMTS service architecture via open standardized interfaces. Regulatory bodies (e.g., European Commission) all over the world pushed for the opening of network interfaces because it would foster the liberalization of the telecommunications services market by enhancing the portability of telecommunications services between networks and terminals. This concept of service portability was called the virtual home environment (VHE) in 3GPP standardization. As regulatory bodies correctly understood, the only way to realize the VHE philosophythat is, to make it possible for third party service providers to develop UMTS applications that can run on several networks and terminals -is to open/standardize the application interfaces toward these networks (i.e., to standardize OSA). Several standardization bodies (3GPP, etc.) and consortia (Parlay, JAIN, etc.) contributed to the philosophy behind OSA. In light of the recent evolutions in 3G standardization, this article further investigates the synergy between the two trends mentioned above: on one hand, the trend in the design of the UMTS network architecture to move toward an all-IP approach, and on the other, the trend in the design of the UMTS service architecture to standardize open network interfaces. The goal of the article is to clarify the implications of an IP-based core network design on the UMTS service architecture and to analyze possible evolution paths, integrating both network and service aspects, toward a complete all-IP UMTS system architecture. The article is organized in the following way. The next section gives an introduction to the VHE concept and its realization via OSA interfaces. We then give an introduction to voice over IP (VoIP) in mobile networks and explain how VoIP can be supported in the all-IP UMTS core network architecture. The article then further analyzes the impact of an IP-based core network design on the UMTS service architecture. Two possible scenarios are discussed for supporting VoIP services in the UMTS service architecture based on the principles of the VHE. Finally, the article concludes by evaluating the coexistence of both scenarios: the classical centralized -intelligent network (IN) type -service control architecture and the new decentralized (OSA) type service provisioning architecture.