Mobile virtual private dial-up services

Virtual private dial-up networking (VPDN) allows mobile users to access the ir corporate networks through the same infrastructure they use to access th e Internet. The data networking industry has produced various protocols-for example, Layer 2 forwarding (L2F) and point-to-point tunneling protocol (P PTP)-to provide VPDN services. Based on these protocols, a new integrated V PDN protocol Layer 2 tunneling protocol (L2TP), is currently being designed by the Internet Engineering Task Force (IETF). However, this solution is o nly meant to deal with a wired network environment. In this paper, we descr ibe and compare different solutions that extend the wired VPDN service mode l over the various wireless access network technologies. The first set of s olutions uses network-layer protocols such as IETF's mobile Internet protoc ol (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 lo cation of the home agent (whether it resides in the access provider's netwo rk or the corporate network) and the availability of a hierarchical archite cture to minimize hand-off latency. The second set of solutions uses both l ink-layer (for example, L2TP) and network-layer (for example, mobile IP) pr otocols to perform macromobility management. Some alternatives require the mobile host to play a more proactive role-for example, the voluntary tunnel ing approach. We briefly describe and compare the two sets of alternatives in terms of their flexibility, hand-off latency and bandwidth overhead.