Mesh technology has both indoor and outdoor applications. Inside buildings, products from Firetide and Strix can be used to create WLANs that don't require Ethernet backhaul. In the simplest ad hoc implementation, you just plug a bunch of mesh-capable APs into electrical outlets in your building and the APs automatically form backhaul connections amongst themselves. Of course, simple is not always optimal, so some products provide the ability to manage the mesh more closely, selecting appropriate links and radio technologies.
Outside the building LAN, meshes can be used to provide wireless access across wide geographic areas measured in miles rather than meters. Tropos has garnered some attention recently because of work it is doing with NASA. Based on tests in the Arizona desert, NASA was able to deploy wireless connectivity covering a two-square mile area using two to three Tropos devices. In urban areas, where buildings cause RF reflections, you might need 10 times as many devices. But for some applications, including public safety and Internet access in suburban or rural areas, the technology has significant potential. BelAir also offers outdoor mesh products, which include multiple radios per access device, and they aren't limited exclusively to 802.11.
The major benefits of wireless meshes include system resiliency, flexible coverage areas and rapid deployment. It's likely that even mainstream WLAN infrastructure vendors will begin to employ some limited mesh capabilities in their products to provide more deployment flexibility in locations where cables are hard to pull (warehouses, historic buildings, etc.).
The Mobile Observer