  Previous studies have shown that the actual handoff schemes employed in the
IEEE 802.11 Wireless LANs (WLANs) do not meet the strict delay constraints
placed by many multimedia applications like Voice over IP. Both the active and
the passive supported scan modes in the standard handoff procedure have
important delay that affects the Quality of Service (QoS) required by the
real-time communications over 802.11 networks. In addition, the problem is
further compounded by the fact that limited coverage areas of Access Points
(APs) occupied in 802.11 infrastructure WLANs create frequent handoffs. We
propose a new optimized and fast handoff scheme that decrease both handoff
latency and occurrence by performing a seamless prevent scan process and an
effective next-AP selection. Through simulations and performance evaluation, we
show the effectiveness of the new adaptive handoff that reduces the process
latency and adds new context-based parameters. The Results illustrate a QoS
delay-respect required by applications and an optimized AP-choice that
eliminates handoff events that are not beneficial.

Networking and Internet Architecture