摘要：Most IPJ readers are familiar with Wireless Local-Area Networks (WLANs; see, for example, IPJ Volume 5, No. 1). Some may even be familiar with recent developments in Wireless Metropolitan-Area Networks (WMANs), such as WiMAX. Although nonproprietary WMAN technologies are still in the standardization phase, the IEEE 802.11 family of protocols has reached maturity and rendered inexpensive (and often free) WLAN access increasingly popular. Both WLANs and WMANs provide high-speed connectivity (in the order of tens of Mbps), but user mobility is restricted. In fact, it is probably more appropriate to talk about "portability" rather than "mobility" [1] when referring to WLANs and WMANs.Wireless wide-area networks (WWANs), on the other hand, allow full user mobility but at data rates typically in the order of tens of kbps. This will change to some extent when third-generation (3G) cellular networks are fully deployed. Still, 3G deployment is slower than originally anticipated, a development often attributed to the combination of high spectrum license costs, the recent economic downturn, and high equipment costs. As a result, both population and geographical coverage tend to be uneven. For example, in Finland, a forerunner in wireless communications, population coverage is well below the 35-percent level, and geographical coverage is even smaller.
