Friday, August 29, 2003
Wireless roofs
Technology Review is carrying a good story on MIT's Roofnet project, which aims to give MIT students high quality/bandwidth access at very low costs.
Each computer and roof-mounted antenna at students’ apartments and MIT buildings is a node on the network and the arrangement in which they are connected to each other—the topology of the network—is constantly changing. “We want to understand how a whole bunch of computers with short-range radios can self-configure a network, forming order out of chaos,” says computer science professor Robert Morris, who coordinates the project. The network has now more than 30 nodes in a 4-square kilometer area surrounding the MIT campus. “We hope to reach a hundred nodes within a few months,” he says.
The project also addresses the need to look beyond the shortest-path strategy of the fixed Internet and to develop something that takes into consideration the attenuation of wireless signals over distances.
Most of the routing protocols now being proposed by mesh network researchers borrow the shortest-path strategy used in the fixed Internet. These protocols try to find the route with the fewest number of intermediate nodes between sender and destination. For the wired Internet—with its nearly static topology and reliable links—this scheme has been working pretty well: our e-mails hop from router to router and reach the other side of the world in a few seconds.
But it turns out that this shortest-path strategy might not be adequate for sending packets through the air. In a wireless network, according to the MIT group, distance matters: the longer the signal has to travel, the more it will degrade. Moreover, the link quality between nodes varies unpredictably due to such transient phenomena as trucks driving by, moisture in the air, or a pigeon sitting on the antenna. The result is a considerable amount of packet loss, transmission errors, and connections that simply appear and disappear throughout the day. A routing protocol that minimizes the number of hops ends up choosing longer distances for each hop—and therefore sending data over low-quality wireless links.
Obviously, I have to wonder whether something similar would work in India, of for that matter in any part of the world where there is a reasonable dense population, enough anyways to justify the cost of installation.
Each computer and roof-mounted antenna at students’ apartments and MIT buildings is a node on the network and the arrangement in which they are connected to each other—the topology of the network—is constantly changing. “We want to understand how a whole bunch of computers with short-range radios can self-configure a network, forming order out of chaos,” says computer science professor Robert Morris, who coordinates the project. The network has now more than 30 nodes in a 4-square kilometer area surrounding the MIT campus. “We hope to reach a hundred nodes within a few months,” he says.
The project also addresses the need to look beyond the shortest-path strategy of the fixed Internet and to develop something that takes into consideration the attenuation of wireless signals over distances.
Most of the routing protocols now being proposed by mesh network researchers borrow the shortest-path strategy used in the fixed Internet. These protocols try to find the route with the fewest number of intermediate nodes between sender and destination. For the wired Internet—with its nearly static topology and reliable links—this scheme has been working pretty well: our e-mails hop from router to router and reach the other side of the world in a few seconds.
But it turns out that this shortest-path strategy might not be adequate for sending packets through the air. In a wireless network, according to the MIT group, distance matters: the longer the signal has to travel, the more it will degrade. Moreover, the link quality between nodes varies unpredictably due to such transient phenomena as trucks driving by, moisture in the air, or a pigeon sitting on the antenna. The result is a considerable amount of packet loss, transmission errors, and connections that simply appear and disappear throughout the day. A routing protocol that minimizes the number of hops ends up choosing longer distances for each hop—and therefore sending data over low-quality wireless links.
Obviously, I have to wonder whether something similar would work in India, of for that matter in any part of the world where there is a reasonable dense population, enough anyways to justify the cost of installation.
