Mobile virtual private dial-up services

Virtual private dial-up networking (VPDN) allows mobile users to access their corporate networks through the same infrastructure they use to access the Internet. The data networking industry has produced various protocols — for example, Layer 2 forwarding (L2F) and point-to-point tunneling protocol (PPTP) — to provide VPDN services. Based on these protocols, a new integrated VPDN protocol, Layer 2 tunneling protocol (L2TP), is currently being designed by the Internet Engineering Task Force (IETF). However, this solution is only meant to deal with a wired network environment. In this paper, we describe and compare different solutions that extend the wired VPDN service model over the various wireless access network technologies. The first set of solutions uses network-layer protocols such as IETF's mobile Internet protocol (IP) to perform macromobility management. In addition, IETF's secure IP (IPSEC) protocols may be used when security features are desired. The first set of solutions differs from the wired VPDN model only in terms of the location of the home agent (whether it resides in the access provider's network or the corporate network) and the availability of a hierarchical architecture to minimize hand-off latency. The second set of solutions uses both link-layer (for example, L2TP) and network-layer (for example, mobile IP) protocols to perform macromobility management. Some alternatives require the mobile hosts to play a more proactive role — for example, the voluntary tunneling approach. We briefly describe and compare the two sets of alternatives in terms of their flexibility, hand-off latency, and bandwidth overhead.