A British start-up is planning to launch managed broadband services in the U.S. that will bond ADSL lines as well as broadband lines from multiple providers.

The company, Sharedband, hopes to launch services initially in Seattle next month, with plans to expand nationwide throughout 2008.

Sharedband’s initial offering uses a bank of managed centralized servers, off-the-shelf routers from Netgear and its own firmware to bond up to four ADSL lines for greater bandwidth speeds. This month, the company is also adding another version using Linksys routers that allows bonding of non-ADSL lines, including those from different providers.

The aggregation of lines adds a 3% overhead to the traffic, which the company says is no impediment to the quality of applications such as voice and video transmitted this way.

“One plus one equals 1.97,” said Keith Collins, Sharedband’s sales and marketing director, of the math dictating the system’s bandwidth speeds. “There are some tolerances as well. The latencies have got to be within a certain amount, or that affects it as well. But if you’ve got some reasonable quality lines, they’ll do. Pretty much add them together.”

The company’s two-person U.S. workforce is currently setting up servers in Seattle in preparation for a two-pronged attack in the U.S., selling both to Internet service providers on a wholesale basis and, initially at least, directly to small and medium-sized business customers.

End users will be able to download the router firmware themselves over the Internet if they want. But the system won’t work unless the user is in some proximity to Sharedband’s servers. The precise reach of the system isn’t known (and distance adds latency to the service), but the company expects its Seattle infrastructure to serve much of the Pacific Northwest.

“We’re happy to give away the software,” Collins said. “It doesn’t work without the aggregation server software at the other end. The business model doesn’t charge for the router firmware at all. The only charge the customer gets is the cost of loading the firmware on at the moment. The revenue stream is earned by the provision of the service to re-aggregate the software on the Internet.”

Sharedband’s system, when deployed with the Linksys WRT54 wireless router, can bond broadband lines from multiple providers, whether ADSL-based or not, allowing customers to couple service from telco and cable providers, for example. Collins says this gives the service more resiliency; should one provider’s service shut down, the other may continue. Users will also receive information on the relative performance of each line, so they’ll know if one broadband provider is underperforming.

“We’re piggybacking on the processing power of the router,” Collins said. “When you plug the routers in to your local area network, one per line, they discover each other and pull together the resources of the lines they’re connected to. They’ll cope with any type of Internet connection. So if they’re connected to 1.5-Mb/s or 3-Mb/s lines or even a T-1 connection, it doesn’t really matter. The algorithm that shares the packets across those different lines adapts itself to what’s available.”

The company has only begun turning up live customers in the U.K., where it will sell only through partners and not directly.