For the third generation mobile systems (UMTS, FPLMTS) an integration with B-ISDN is foreseen. This integration is not limited to service integration (common services for mobile and fixed networks), but also aims at reusing B-ISDN switching and transport infrastructure. In this paper the UMTS Mobility Server is presented as a solution to support third generation mobility in ATM. The Mobility Server is a dedicated network element that handles the specific mobility functions. As such, it has a very limited impact on the existing B-ISDN switches. The mobility functions that are performed by the Mobility Server are: transport interworking/integration, bridging, macrodiversity and combining, and seamless handover.
The Mobility Server can be located at CSS and/or LE level. All mobility functions can be implemented at both levels. Some of these are radio interface dependent. The choice of the allocation of the Mobility Server depends on the specific environment (e.g. urban city, rural low density, highway) and on the required network functionalities (e.g. handover, macrodiversity). The Mobility Server can be used for the GSM, DECT or new radio interfaces such as ATDMA and CDMA.
The Mobility Server does not only limit the impact on the standard broadband switches or B-ISDN transport infrastructure, but also provides a modular introduction of mobile communications in a fixed B-ISDN network and allows for a gradual network evolution. Furthermore, the infrastructure can be extended in a flexible way as the mobile communication segment increases.