A VPN-driven Infrastructure for Vertical Handovers

Mobile PCs are equipped with a multitude of network access technologies, such as IEEE 802.11 WLAN, GPRS over GSM or wire-based Ethernet. If the user wants to access the Internet he has to choose one of the technologies and has to use it for the whole duration of the session. But this is problematic when the user wants to be mobile and has to change network access technologies. It was quite problematic so far to start a session using Ethernet (rarr laptop at work) and then perform a seamless vertical handover to WLAN when the user becomes mobile. The protocols used in the Internet were not designed with mobility in mind. Some proposals were made to circumvent these problems, for example by using enhancements like Mobile IP or IPv6, but a solution that could easily be applied to a multitude of different " real-world systems" has not been presented yet. We developed a method that implements a data transfer mechanism that is able to handle the problems caused by mobility and vertical handovers. Our first approach made use of the universal proxy protocol SOCKSv5 (RFC 1928) to relay all data to a central proxy server using a handover-capable transport mechanism. Here, "socksified" applications were needed, which was not feasible in all possible scenarios [Evers, 2004]. This paper presents our latest enhancement that makes use of a virtual private network (VPN) in combination with our handover capable transport mechanism. This offers a full VPN- based network access to all applications running on the mobile node and is able to do all handover related work transparently. VPN-clients are available for all relevant operating systems. The handover management software was implemented using C++ and runs on GNU/Linux, Mac OS and Microsoft Windows. The architecture offers full mobility to the end user without the need of modifications to the applications or the operating system itself.