SkyPilot, a mesh-networks start-up based in Menlo Park, California, is taking a similar approach. Its rooftop units use smart antennas to beam data back and forth, enabling frequencies to be reused more efficiently and increasing capacity. Duncan Davidson, the firm’s boss, says the Internet/mesh approach has many advantages over the traditional circuit-based approach used in telephony. “The Internet architecture gets better with density [whereas] the phone system gets worse,” he says.
The problem with the mesh approach, however, is how to get it off the ground. Who will build the NAPs to seed a neighbourhood? Unlike Nokia, which simply sells its RoofTop gear to ISPs, SkyPilot plans to help prime the pump itself, by setting up NAPs and allowing ISPs to resell access. This approach also has technical merit: multiple overlapping mesh networks are far less efficient than a network in which all the nodes can talk to each other. So it makes sense to have competition at the ISP level, rather than the infrastructure level.
Perhaps the most ambitious vision of mesh networking is that of MeshNetworks, a firm based in Maitland, Florida. It has developed its own radio hardware and some clever routing software that makes it possible to blanket an area with broadband wireless coverage using “intelligent access points” (its term for NAPs) and shoebox-sized wireless routers. But what is really clever is that this wireless mesh-network then supports mobile devices, such as handheld computers and laptops. And those devices can also act as routers for other mobile devices, further extending the mesh. Cleverest of all, even when two or more devices are beyond the range of a NAP or a wireless router, they spontaneously form their own local network. MeshNetworks’ technology thus combines the mesh architecture with the even more radical approach of “ad hoc” networking.
From the Battlefield
As the name suggests, ad hoc networks consist of multiple devices, each of which also acts as a router for the others. Furthermore, these devices may also be moving, so that the network topology is in constant flux. This poses a number of challenges, not least in routing. Clearly, the quickest way to send a packet of data from one device to another changes as the devices move around, and other devices join and leave the network..
Ad hoc networks are commonly associated with military and emergency applications, both of which have to operate in situations where there is no network infrastructure. For that reason, ad hoc networks are sometimes referred to as “infrastructureless” network architectures. Rescue workers in an earthquake zone, for example, could use handheld radios, each of which also acts as a relay for other nearby radios. Similarly, the robust, self-healing properties of ad hoc networks make them suitable for military use, either by mobile combatants, or to connect up “smart dust” sensors that would be sprinkled across a battlefield from an aircraft.
For many years, says Zygmunt Haas, a researcher at Cornell University, most research into ad hoc networks focused on military applications. Recently, however, interest in the field has increased as its commercial possibilities have started to emerge. “Bluetooth”, a short-range wireless protocol that enables mobile phones to talk to nearby handheld computers, printers and other phones, is a simple form of ad hoc networking, though it supports only single “hops” between individual devices.