Discussing the Dynamics of Mesh

By Adam Stone

June 28, 2004

MeshDynamics thinks a multiple radio approach to bigger hotspots is the only way the public access space will make it.

There are those who say the hotspot model of Wi-Fi access can never be a money maker, on the grounds that you can't get enough people using a single hotspot at one time to make the thing pay off. The solution, they say, is an interconnected series of hotspots -- a hotzone or maybe a hotspot mesh, if you will -- distributed across a broad geographic area, such as a downtown business district.

That's where MeshDynamics comes in. Founder Francis daCosta describes the fundamental problem associated with the single-hotspot model as one of degradation of bandwidth. The more people on the network, the less bandwidth there is to go around. That's not a problem with ten users, "but you cannot get 1,000 users in one Starbucks. You lose all the bandwidth within one or two hops," he explained.

One solution is a mesh network, in which those 1,000 people share ten access points on a common network. This can be done, but there is a snag within the typical scenario in which each access point employs a single radio.

If each access point uses a single radio, daCosta explains, we run into the same problem of signal degradation. Devices conflict with one another, and must share bandwidth as the signal travels along a common channel. In effect, bandwidth degrades by half at each hop, until at four hops away the maximum bandwidth available is just one-sixteenth of the total available bandwidth.

This degradation is a product of the single-radio topology. MeshDynamics has therefore designed a multiple-radio mesh, in which each access point receives and transmits signal using more than one channel and more than one radio. To manage network traffic, all the channels are dynamically and automatically allocated. This in turn creates a network that can be scaled without losing bandwidth.

It's a promising scenario, said Curtis White, a commander's representative at the Air Force Research Lab. He is looking at MeshDynamics as a prospective contractor to the military.

The multi-radio mesh concept "gives me latitude in terms of scalability, in terms of the sheer numbers," he said. "There is only so much radio space, and having single radios limits you in the topologies you can manifest. Having the multiple radios just gives me a much more flexible system."

Industry observers say the multi-radio scheme could help to solve a fundamental problem in current mesh networks. "If the devices in a network are all in the same channel, the amount of time a device can spend transmitting is reduced by the number of other devices on the network," explained Lee Chinitz, chief technology advisor at network-device manufacturer Proxim.

Chinitz sides with those who feel that a single-hotspot economic model may not be feasible in all situations. He points to the collapse of San Francisco-based startup Cometa. The hotspot operator had originally predicted it would have 15,000 hotspots in place by 2005, but it never managed to get enough access points in place to support its claims.

Some say the Cometa scenario may be typical of the problems plaguing hotspot operators. Specifically, daCosta and others argue that with a single hotspot, there just is not enough room on the network to bring in the number of users you would need to reap significant rewards.

If the solution is to go outdoors, to create a Wi-Fi network that spans a street or a neighborhood, there normally would be added costs in the form of additional Ethernet lines -- but not with a wireless mesh. "If you have devices that can hook up to each other wirelessly and are intelligent enough to be routing the traffic between them, you could extend the coverage area" without additional cost, Chinitz suggested.



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