There are indications that the next generation mobile communication systems will shift away from the traditional vertically integrated approach in system design and instead allow access to a set of services through a variety of heterogeneous access technologies. With the emergence of multimode mobile devices, the next step in the integration of heterogeneous mobile networks, i.e. inter-access service continuity, gains relevance. This paper reviews emerging heterogeneous access networks and their integration, and studies service continuity, including the relevance of Mobile IPv4 and Mobile IPv6 and other mobility solutions at, above, and below IP layer, in this context. We propose a new system architecture, which combines Mobile IP and IPsec in a 3GPP operator environment As part of the proposed framework we present new techniques for mobility security association bootstrapping and for enhancing the mobile device's NAPT traversal implementation. The selected architecture is evaluated using an experimental laboratory setup. The results are used to build up an analysis of the solution and draw up some conclusions.
