The paper analyzes some of the major network topics arising in the UMTS design process. This is done by invoking functional and architectural issues with relation to both the B-ISDN/IN context and the radio access features. The integration of UMTS with the "core" network is discussed by showing functional and network architecture as as well as protocol aspects. A comparison with the solutions adopted for the actual cellular systems, highlights the improving elements characterizing UMTS. Specific UMTS functional schemes are analyzed for call handling and location management procedures. Functional and design issues are also discussed for the radio access part of UMTS. The handover procedure, heavily affecting the architectural choices to be performed, for the UMTS base station is described, and its use in the design process is presented. Basic performance evaluation topics, tied to the achievement of "optimal" solutions for the functions allocation to the network entities are discussed. The paper is based on the work performed within the RACE Project 2066, named MONET.