Fast Connection Recovery in WLAN-to-Cellular Vertical Handoff

Wireless LAN-to-cellular vertical handoff involves time consuming procedures that may significantly disrupt realtime communication. This situation is compounded by the fact that WLAN coverage may sometimes be lost very abruptly and without warning. In this paper we propose and investigate the use of a Vertical Handoff Support Node (VHSN) which is attached locally to the wired LAN hotspot infrastructure. Unlike proxy forwarding and wireless multi-hop schemes, the VHSN does not extend wireless coverage or perform infrastructure-based packet forwarding. The VHSN also does not communicate directly with any mobile station. Instead the VHSN functions as both an (Eth-ernet) LAN and cellular end station. When abrupt loss of WLAN coverage occurs, the VHSN quickly intercepts and redirects the media flow through the local cellular basestation using its cellular end station attachment. This action can quickly recover the connection before the remaining vertical handoff is executed. There are a number of key advantages that this mechanism has over existing forwarding/relaying techniques. Results will be presented which show the performance improvements which are possible using this approach.