Funny thing about wireless networks, they demand a heck of a lot of wires. All those access points that extend your network over the air are connected by wires to the Ethernet LAN.

In a building with Category 5 already running everywhere or in a confined location like a coffee-shop hot spot, the wiring issue might not be such a big deal, but what happens when you're faced with a setting where stringing wires is impractical? Or what if you need to reconfigure an existing wireless network on the fly, or if you need to set up a new network in response to a time-specific event? Or what if you want to provide Wi-Fi to a college or corporate campus, or to a downtown area?

In these cases, wireless mesh technology might be the answer.

The Defense Advanced Research Projects Agency (DARPA) began studying mesh technology in the mid-1990s for use in battlefield communications. Soon after, research-and-development companies such as SRI International began looking at wireless meshes, and now a number of start-ups say this technology will help them transform the wireless landscape.

Simply put, wireless meshes use a topology of redundant connections between nodes to create a self-configuring, self-healing network. Because very few nodes need to be wired into the network, mesh networks limit the need for expensive backhaul while providing additional benefits such as dynamic optimized routing and automatic load balancing.

Mesh vs. mesh

Not all mesh topologies are created equal - some include client devices in the mesh, most don't.

In a pure client mesh, every device in the network, including laptops, PDAs and smart phones, can pass along traffic for other devices, which lets users "hop" through neighboring devices or wireless routers to communicate with each other and to reach the wired network. This "multi-hopping" capability creates a meshed network that automatically routes around congestion and line-of-sight obstacles, while improving throughput as more clients enter the network.

In an infrastructure mesh, access points and wireless routers carry the traffic back to the wired network. In the infrastructure camp, you'll find Tropos, Firetide and BelAir.

"In our system, the clients don't participate in the mesh at all," says Bert Williams, vice president of marketing for Tropos Networks. "They attach to the mesh, but the meshing itself is done by infrastructure devices."

MeshNetworks and PacketHop let clients actively participate in the mesh, but it's not accurate to call either of them pure client-mesh companies. Instead, both rely on infrastructure nodes for the core of the mesh network. Then, once a mesh infrastructure of access points or routers is in place, clients can be used to extend the coverage area, fill coverage gaps and communicate directly with nearby devices.

"I would actually split the mesh world up differently," says Michael Howse, CEO of PacketHop. "Rather than client vs. infrastructure meshes, what I see are fixed vs. mobile meshes. The fixed-mesh companies string together access points. There is one wired node that provides backhaul, with other wireless nodes on the same subnet." There are benefits to this, Howse says. The wireless-mesh nodes provide better coverage, while also distributing intelligence. "The problem with this model is that you will compete with Cisco, Proxim, Symbol and other access-point providers."