An early, and obvious, method is some sort of point-to-point connection. In practice, point-to-point networking has a number of limitations. For one, there is a physical limit to the length of the network, and second, it is difficult to add and subtract devices from the network.
Most obstacles have been overcome by a configuration called “star.” In this topology, computers and other networked devices, such as printers, are connected to a central hub. Adding intelligent switching and power to the hub increases network reliability and distance. Most Ethernet installations use a star topology today.
With either method, there remains a problem. What happens if there is a break in the wire? Problems can range from the loss of one or more devices at the end of a star arrangement to the loss of the entire network in many point-to-point arrangements. And in industrial control applications, even a brief outage is unacceptable.
Enter a concept called mesh networking. According to Kevin Jurok, an engineer for Invensys/Foxboro who designed its version of mesh networking, mesh means that there are alternate paths to get from one place to another. He contends that steady improvement and availability of commercial-off-the-shelf networking products such as intelligent switches have propelled Ethernet implementation in industrial control. Link this with “mesh-aware” devices to hook to the network and network control software, and a resilient, fault-tolerant, self-healing, multi-path network is possible.
This technology is still at an early stage of development at the Foxboro, Mass., unit of London-based automation supplier Invensys (www.invensys.com). Jurok says, “We’re moving to mesh in our I/A Series because of the fault tolerance. However, mobility is another good reason to look at this technology. This means the ability to easily move devices physically around the network or add devices to the network, yet make it very simple for field technicians to accomplish. What makes the system work is a combination of commercial-off-the-shelf Ethernet components, mesh-enabled smart devices and software.”
Most of the publicity surrounding mesh networking involves wireless technology. George Karayannis, vice president at wireless component manufacturer Helicomm (www.helicomm.com), in Carlsbad, Calif., states, “Relatively few companies have deployed low-speed wireless networks for remote monitoring and control applications, due to concerns about the cost and complexity. Two related emerging global standards, ZigBee and IEEE 802.15.4 (promulgated by the Institute of Electrical and Electronics Engineers, www.ieee.org), aim to eliminate these concerns and accelerate the market for low-data-rate wireless products worldwide.
“With 802.15.4,” continues Karayannis, “the IEEE standards body has specified a global standard for reliable and secure low-power wireless communications. The ZigBee Alliance (www.zigbee.org), a global, non-profit industry consortium, is defining the network, security and application profile layers to provide 15.4-based products with enhanced wireless system reliability, security, scalability and interoperability.”
With all the hype surrounding wireless mesh networking and talk of future growth, a legitimate question to ask is whether there are any viable applications. Adrian Tuck, executive vice president of wireless technology supplier, Ember Corp. (www.ember.com), of Boston, points to one of several working applications.
“We have a customer who builds control systems for HVAC (heating, ventilation and air conditioning) applications in motels,” he reports. “The problem is to retrofit existing independent heating and air conditioning units in motel rooms with a central system to reduce energy expenditures. A combination of room motion detectors and front desk control to set air conditioning or heating systems would be a tremendous benefit to motel owners as well as the utility companies. The system adds a controller with wireless mesh networking built in to each HVAC unit. All communicate to a master controller in the office. The system is easy to install, easy to use and easy to adapt.”
Gary Mintchell, [email protected]
