ABSTRACT
Seamless vertical handoff is the ability of a mobile terminal to successfully or simultaneously attach to different access points in an integrated wireless network infrastructure in a way that makes the physical movement two types of wireless networks transparent and preserves application-level connectivity. To achieve seamless handoff, handoff decision algorithms, handoff metrics, and mobility handling to maintain ongoing user connections must be addressed. Traditional handoff decision metrics based on the received signal strength (RSS) and other physical layer parameters are insufficient for the challenges of a heterogeneous wireless system because the upper-layer applications are really interested in metrics related to network conditions (such as available bandwidth and delay) and user preferences. To make an intelligent and better decision on which wireless network should be chosen to deliver each service via the network that is the most suitable for it, the following context-aware metrics have been proposed for use in addition to the RSS measurements: perceived QoS and QoS requirements of sessions; user preferences such as a preferred wireless access network; terminal capabilities such as supported access networks, protocols, and available resources; status of the networks; location of the mobile host; and monetary costs involved in changing wireless networks.
