The emergence of metro-scale Wi-Fi

Computerworld - Last week, I wrote about WiMax, and I briefly mentioned the rapidly emerging metro-scale Wi-Fi opportunity. Far beyond the original concept of a hot spot, the approach now is to literally blanket a metropolitan area with Wi-Fi coverage and provide a cellular-like connectivity experience.

I first started talking about this concept back in 1998, and I remain convinced that this is one of the most important directions for wireless. In fact, the future of cellular and Wi-Fi are inextricably bound together -- a surprising conclusion considering that so many believe metro-scale Wi-Fi threatens cellular progress. Nothing could be further from the truth. And the benefits of such a combination for enterprise users will be enormous.

Let's start at the beginning. Wireless LANs have traditionally been thought of as an indoor and short-range -- but still a broadband -- technology. The idea was simply to replace the wires binding users of otherwise mobile computers to the wall with air that could offer the performance of wire. WLANs have been an enormous success in the residence (most homes are, after all, much more difficult to wire than most businesses), and, thanks to centralized WLANs based on wireless switches, are now spreading rapidly in the enterprise as well. With home and work covered, the final frontier is everywhere else -- public spaces.

The problem with wireless LANs in these venues, however, is the core challenge that any cellular network faces -- backhaul. The interconnection of outdoor access points would normally be the source of most of the expense in deploying metro-scale WLANs, but this isn't the reality we see today. Rather, we can interconnect the access points (AP) wirelessly, using a technique based on the concept of a mesh.

A wireless mesh allows APs to be connected only to power and then to interface with the rest of the infrastructure by relaying information to other APs -- in other words, the backhaul is wireless. This allows an operator to quite literally blanket an area with APs and provision over-the-air backhaul at basically zero cost for this interconnect. As customer demand, traffic volume, time constraints and cash flow allow, additional wired backhaul can be added to improve performance. In a purely wireless mesh, backhaul and user traffic can compete, although even this problem can be mitigated by adding more nodes or radios per mesh node. More backhaul interconnections to points outside the mesh (normally the Internet) mean greater overall capacity, higher throughput and better support for time-bounded traffic like voice-over-IP over Wi-Fi (or what we call VoFi).