Many protocols populate factory nets

The biggest challenge for manufacturers planning to migrate their factory floor networks to Ethernet and Internet protocols is their huge investments in legacy equipment.

Until now, manufacturers used special-purpose network protocols such as Rockwell's ControlNet, Siemen's Profibus and Schneider Electric's Modbus Plus to connect industrial devices. Designed for heavy-duty use, these protocols provide ultrareliable connections and are offered in rugged hardware that can operate at high temperatures and in environments with lots of vibrations.

Many manufacturing plants run several of these industrial network protocols as well as Ethernet to connect PCs on the factory floor. Manufacturers see cost savings in pushing Ethernet down to the control systems first and ultimately to the devices, thereby eliminating other protocols and creating flatter networks.

"There are two kinds of networking technologies on the shop floor: There is the wiring between the machines, and there is the wiring between the PCs that control the machines," says Paul Swamidass, a professor at Auburn University who has studied factory automation. "The PCs are using Ethernet/ Internet technologies, but the machines may not be. Now they're putting everything on the Internet."

The industrial protocols are being rewritten to support Ethernet and TCP/IP, and products that comply with the new standards are starting to hit the market (see graphic).

In a handful of cases, Ethernet and TCP/IP are replacing the ill-fated MAP/ TOP network protocols that died along with the Open Systems Integration movement. Backed by Boeing and General Motors, MAP/TOP failed to catch on with industrial users because it was too complex.

"Users were not able to come to an agreement on the MAP/TOP specification, and it never had the product support," says Jack DeLeon, general manager of the communications business at Rockwell Automation. "The customers who installed [MAP/TOP] are migrating to Ethernet as fast as economics allows."

Until recently, Ethernet wasn't sturdy enough to handle industrial applications that require millisecond response times and 99.99% uptime, says Anthony Cinalli, vice president of technology at GE Cisco Industrial Networks.

Recent improvements in Ethernet performance and reliability make it a better fit for the factory floor. In particular, Ethernet can be switched to ensure that critical data gets priority - a feature known as determinism

Ethernet also offers better scalability than special-purpose industrial networks and lower maintenance costs.

"Now manufacturers have to train their people in multiple protocols and keep spare parts for lots of different networks," Cinalli says. "Ethernet offers savings in training and maintenance costs."