摘要：P opular mobile devices now ship with several integrated wired
and wireless network interfaces. Personal Digital Assistants
(PDAs) and smartphones, for example, are increasingly sup-
porting communications through both cellular technologies and
Wireless LANs (WLANs); laptops typically come with built-in
Ethernet, Wi-Fi, and Bluetooth[1]
. As multiaccess devices proliferate,
we move closer to a network environment that is often referred to
as “beyond 3G” (B3G). Key success factors for cellular third-gener-
ation (3G) communications include better cell capacities, increased
data rates, transparent mobility within large geographical areas, and
global reachability. For B3G, the next frontier lies beyond transparent
mobile connections within the same access technology because users
will expect to be globally reachable anytime, anywhere, and remain
“always best-connected” (ABC)
[2]
. In order to select the best possible
connectivity option (anytime, anywhere), mobile devices and access
networks will have to work together in order to enable users to take
full advantage of all available options.
