In a mesh network, adding nodes multiplies its strength
Return on investment for the ad-hoc networks is attracting the interest of governments and citizens
- By William Jackson
- Jul 30, 2004
Wireless mesh networking holds the possibility of letting communities extend broadband access on the fly and on the cheap to public safety officials, municipal employees and citizens.
But just what role the emerging technology will play still is being worked out, said Daniel Aghion, executive director of the Wireless Internet Institute of Boston.
'I wouldn't call it mature, because there are few places where broad deployment has been done,' Aghion said.
Tests and pilots are beginning to yield reliable results, however, and the return on investment in communities where it is being deployed is making ad-hoc networking attractive.
Wireless mesh networking is a technology developed by the Defense Advanced Research Projects Agency for creating multihopping IP networks in which individual nodes are wireless routers. This eliminates the need for cellular or radio repeater systems that traditionally pass radio signals from dumb nodes.
The networks are ad hoc because the routing nodes can be mobile and the architecture is constantly shifting, with new routing tables being created as nodes move in and out of range of each other.
'The more devices are added, the more reliable they are,' because more nodes become available for routing traffic, said Michael Griffin, assistant chief of the California Governor's Office of Emergency Services.
California's Office of Emergency Services recently participated in an interagency trial of the technology in the San Francisco Bay area.
A number of companies are commercializing the DARPA technology, using different approaches.
PacketHop Inc. of Belmont, Calif., uses a software solution, with client programs that can be loaded on notebook and handheld computers. The computers can use most types of wireless network interface cards. A network controller appliance acts as a gateway between mobile and wired segments. This is the scheme tried out by the Golden Gate Safety Network in the first test of the products. Users were able to use the system with almost no training, Griffin said.
MeshNetworks Inc. of Maitland, Fla., uses its own PC Cards in mobile computers and vehicle-mounted modems to listen for other nodes on the network. This system has been implemented in Medford, Ore., to give police cars, fire trucks and ambulances high-speed connections to the city's wired network.
Bandwidth available to the end user varies depending on protocols used to transmit IP over radio frequencies, but practical speeds can range from a few hundred Kbps to 1 Mbps, both upstream and down.
In this country, municipalities are among the early adopters of wireless mesh, with a handful of systems implemented. Many more communities are waiting to see if the technology can fulfill its promise.
Although many communities would like to be able to offer broadband access as a utility, the first implementations are showing up in public safety. Police and fire departments offer a closed environment where it is easy to conduct pilots with a host of applications that can be accessed for a quick return on the investment.Beat goes on
San Mateo, Calif., a city of about 110,000, installed 30 fixed mesh access points to cover a five-square-mile section of the city. Using WiFi notebooks to access data and print reports without coming into an office allows its 30 police officers to stay on the beat 25 percent longer.
'That's a huge productivity gain,' with an estimated payback time of six or seven months, Aghion said.
Medford, Ore., spent about $200,000 on its mesh network, in addition to a $500,000 grant from the Homeland Security Department. Technology director Doug Townsend estimated the city would recoup its share of the investment in about eight months with better productivity. Those savings do not include anticipated reductions in the police department's cellular phone bill.
But whether and to what extent public safety networks should be shared with other departments is a question that still needs to be worked out.