Oregon city builds mesh network
- By William Jackson
- May 19, 2004
A meshed wireless data network in Medford, Ore., will give police cars, fire trucks and ambulances high-speed connections to the city's wired network.
Funded in part with a $500,000 grant from the Homeland Security Department, the wireless network will let users do 'whatever you can do from a desktop system, but from any place in town,' said Doug Townsend, Medford's technology director.
It will use technology developed by the Defense Advanced Research Projects Agency for ad hoc, multi-hopping IP networks with individual nodes instead of radio repeaters.
MeshNetworks Inc. of Maitland, Fla., commercialized the technology and is supplying the wireless network. 'This is being deployed primarily as a mobile data system,' said Rick Rotondo, MeshNetworks' vice president of technology, although city officials eventually want to use it for voice and video.
Medford, a city of about 70,000, is the seat of Jackson County. All its police and fire vehicles have mobile computers, mostly the Panasonic Toughbook CF-27, deputy police chief Ron Norris said. The computers handle not only dispatching but also data lookup from the wired network and report filing.
The wireless mesh replaces a General Packet Radio Service network with limited bandwidth. Maintenance was becoming expensive, Townsend said, and on top of that, the police department's cellular phone bill is about $3,000 a month.
So Medford went shopping for an up-to-date system to upgrade its capabilities, interoperate with county departments and replace the cell phones.
'We don't have a common system in Jackson County. That's our goal'to go throughout the whole county,' Norris said. 'We want to do voice over IP. Our cell phone cost was a factor, and we were looking for a system that doesn't degrade as more people come on.'
Maximum bandwidth of the city's MeshNetworks Enabled Architecture is 2 Mbps, but practical speeds range from a few hundred Kbps to 1 Mbps, Rotondo said. Because there are no repeaters or routers, those speeds hold for both upstream and downstream traffic. The mesh can scale up from a two-person, point-to-point link to a wireless metropolitan network.
'Every node acts as a router-repeater for every other node,' Rotondo said.
MeshNetworks PC Cards in the mobile computers as well as vehicle-mounted modems listen out for other nodes in their neighborhood.
'We build a routing table at each node,' Rotondo said. 'That is all transparent and handled in background.' Optimal routing depends on latency, error rates and throughput.
Because the nodes rely on each other to complete hops, 'the more users you have, the more robust it is,' Rotondo said.Stationary access points
To ensure that a mobile node is never out of range, the city is installing stationary wireless access points. They differ from radio repeaters because they do routing, just as the mobile nodes do. An intelligent access point is the bridge between the wireless mesh and the wired network.
The location of each node is tracked using time of flight and triangulation. Even if a vehicle is moving at 60 miles an hour, 'we can locate it to within about 10 meters,' Rotondo said.
Dispatchers will use a mapping application that incorporates the location data.
Medford kicked in about $200,000 for the first phase of the wireless deployment, which covers its 24-square-mile area. The first 100 mobile users are emergency responders, but coverage eventually will expand to other city employees, Townsend said.
The city is seeking another DHS grant for a second phase that would extend into growth areas outside the city. A third possible phase would cover population concentrations throughout the county. Townsend said each phase would probably cost another $500,000.
Norris said the police department replaces a third of its mobile computers each year, but no new computers are needed to use the network'just the MeshNetwork PC Cards.
Townsend said the city probably would recoup its $200,000 investment in about eight months with better productivity, even without eliminating cell phone bills.