Evolving core networks from GSM to UMTS R4 version

More than 217 UMTS licenses have been issued by June 2007. Mobile operators, especially those with GSM legacy networks, prefer UMTS R4 technique to evolve their existing 2G GSM networks. UMTS R4 technique provides a smooth path to bridge legacy TDM-based network to an IP-based soft-switched network. This paper describes the basic architecture and topology of UMTS R4 core network and introduces two options in network planning: flat structure or layered structure. To propose an evolution path, the paper then suggests a 'threelayer structure' solution to seamlessly converge UMTS R4 core network with legacy GSM core network. The proposed solution approach achieves the all-IP vision and is capable of convergence with IMS and EPC.