One of the most challenging aspects in Next Generation Networks (NGNs) is the mechanism through which the different technologies will complement each other to achieve a constant access to networks. This research work deals with the problem of defining fast movements without interruptions (seamless handoffs) in NGNs. This objective is achieved through a secure key distribution process, which enables a fast re-authentication process providing both user anonymity and untraceability. The developed access control system offers a set of features not covered so far by a single solution: (1)...