Primer: Wireless Mesh Networks
What is it? In a mesh network, the wireless connection extends not only to client computers, such as wireless laptops, but between other network nodes. This is in contrast with a typical wireless local area network, where the client computers connect wirelessly to an access point but that device is in turn plugged into the wired corporate network. The connection between the local area network and a larger corporate network or the Internet is known as the "backhaul."
In a mesh network, the access point is connected to a wireless router (or the two may be combined into one device). That router, in turn, hands off a network transmission to one or more other routers before the signal reaches a wired connection. In much the same way that a standard router chooses from many possible paths across the Internet, a wireless router scans radio connections to find the least congested path.
Wireless backhaul makes it possible to cover large areas more economically than if each access point had to be provided with a wired connection.
Who are the vendors? Motorola became the biggest entrant with its acquisition of MeshNetworks last year. The MeshNetworks products were derived from military research and employ a proprietary radio networking protocol, rather than the Wi-Fi (802.11 protocol) standards that support familiar consumer applications such as coffee-shop hot spots.
Motorola says its technology handles radio interference and connections with moving vehicles better than 802.11. However, this year Motorola is introducing a new product that can communicate by either its proprietary protocol, 802.11, or a new licensed 4.9 gigahertz public-safety band for data networking.
Other startups, such as Tropos and Firetide, are adding their own wireless routing technology. For an open-source option that can be assembled from commodity PC and 802.11 networking hardware, look at LocustWorld (www.locustworld.com) or one of the products based on its software.
Who's using it? Much of the interest in this technology has come from municipalities wanting to provide citywide data networking to police, firefighters and other public employees. Some cities and grassroots organizations are offering Internet access via mesh technology; the city of Philadelphia is planning an ambitious project of this sort. Cities often can mount the required equipment on light poles throughout an area.
Richard A. Bull, police chief of Ripon, Calif., says his city is using Motorola gear to eliminate its dependence on data networking from cellular carriers. In the process, city departments get access to higher-bandwidth applications such as interactive mapping and video streaming from surveillance cameras, he says.
"If there's a disturbance at a truck stop in town, the officers can pull up a feed from the camera and see what's going on before they even get there," Bull says.
Commercial applications are rarer, but Firetide cites as a customer a Holiday Inn in Bluefield, W.Va., that deployed mesh infrastructure because the franchisee needed to meet a mandate for providing guests with Internet access but wanted to avoid tearing up walls to run cables. Motorola has customers in the mining industry that use mesh networking to provide data services to the drivers of earthmoving vehicles and to personnel down in tunnels.
In general, mesh networking makes sense if the network must be deployed over a large area, the organization wants to avoid running wires to access points, or both.
When doesn't it make sense? If you can accomplish your goals with 802.11 access points and wired backhaul, there may be no reason to look at wireless mesh technology.
Within an office building, there's probably no reason to spend up to $2,000 on a wireless mesh router instead of plugging in a standard $100 wireless access point. A price difference of 10 to 20 times is typical, says Motorola mesh networks marketing director Rick Rotondo. "You can pull a lot of wire for that," he says.
But where wiring is impractical, mesh can extend the reach of wireless.