Municipal Mesh Network

Protocols developed at MIT are helping the city of Cambridge to go wireless.

The residents of Cambridge, MA, may soon be able to log onto the Internet from any bus stop or city park. The city is working with MIT to go wireless, with a special focus on giving low-income residents access to the Internet.

The project is based on an experimental system called Roofnet, an unplanned, multiroute mesh network developed at MIT's Computer Science and Artificial Intelligence Laboratory. A mesh network is a series of radio transmitters and receivers randomly dispersed over an area. To get data from one part of the mesh to another, the network must figure out the best route between them, which can change depending on network traffic, data rates, and even the weather.

Roofnet has been operating for about three years across an area of roughly four square kilometers near MIT, using a few dozen transmitting/receiving nodes and one wired Internet connection through MIT. The nodes have been located in the homes and offices of volunteers, most of them MIT students and staff.

A node consists of a small box containing a hard drive, software written by the researchers, and the same kind of radio card used in laptops, operating on the Wi-Fi standard. There's an Ethernet port, into which a user can plug his or her laptop, and a connection to an antenna. Generally, an antenna has been attached to a roof, with a cable running in a window. But that has required flat roofs and users who can get up on the roof to install the antenna. Now Roofnet is experimenting with antennas that can be placed in windows; they won't get as much coverage, since the signal can't pass through the building, but they're easier to use.

The original idea behind Roofnet was to exploit the benefits of a random, unplanned network. "It's not like making a cell-phone network, where you have to plan very carefully where the cell towers go," says Robert Morris, associate professor of computer science at MIT, who heads the project. With simple-to-use equipment that requires minimal maintenance, the Cambridge-wide network could be inexpensive and grow organically. The downside is that in some areas, where a node is far away from its nearest neighbor, the service can be unacceptably poor.

Cambridge plans to remedy these coverage problems by attaching antennas to as many tall buildings as possible. Jerrold Grochow, MIT's vice president of information services and technology, says the city views the project as a utility, like providing electricity for street lights. "It's not meant to compete with someone in their home buying cable modem or DSL service," he says.