Wireless Networks: Self Healing Capabilities Offer Edge
The self healing capabilities of wireless networks offer an edge over traditional wired technology.
In the wired versus wireless debate, network cables have always been touted as the most reliable solution. That’s likely to change in coming years as wireless architectures bring self-healing capabilities to the networking world.
When nodes on wireless networks fail, modern peer to peer architectures have the ability to find alternative paths, sending signals to other nodes until they find a pathway to the desired node. These self healing networks provide fault tolerance that wires can’t provide.
“Fault tolerant protocols are much easier to integrate in wireless networks. There are plenty of connections to switch to if one is broken,” says Dr. Gerd-Ulrich Spohr, innovation & technology specialist for Siemens AG Industry Automation Division. Spohr is one of the long-term planners who helps Siemens determine where to invest its efforts to develop technologies that will form the basis of future generations of products.
Intelligent systems can easily choose different paths when the primary route is unavailable. That’s in sharp contrast to conventional wired networks. Most wired networks have a single physical path, those with two or more alternative paths are uncommon because of the costs of duplicate wiring. “Normally in industry you have a line or a ring. If there’s physical damage and there’s no alternative, there’s no way signals can get through,” Spohr says.
The need for these self healing networks will grow rapidly over time. Many new areas will emerge when sensor networks make it cost effective to manage remote sites from afar. The growth of wind and solar farms will be a driver.
It will be very expensive to service offshore wind farms, for example. In applications with high servicing costs, networks will have to be extremely reliable and tolerate errors. That means self-healing networks will see plenty of growth.
“Fault tolerant networks will be very useful for any remote automation where servicing cannot be done easily,” Spohr says. “There will be more and more of these types of installations, so this type of network will see far more usage.”
Though there are areas that need a lot of development, the basic communication technologies for this type of networks is already in place. “There’s no need for anything brand new, most of the wireless protocols already in place have some parts that assist in fault tolerant use,” Spohr says. “There will be progress in the existing protocols which will improve them, but nothing significant is needed.”
Spohr predicts that sensor networks will be the first big application for these wireless networks. The mesh architectures that are now seeing use in somewhat limited applications could grow quite rapidly.
For wireless to have truly widespread acceptance, engineers will have to ensure that battery replacement isn’t a problem. If there’s wiring for a power source, it makes more sense to use that wire to transmit data as well as power. And if the location’s too remote for wiring, it may well be too remote for easy access.
“It will be a real boost if people solve this energy problem, energy harvesting is getting a lot of attention as a solution,” Spohr says. “When there are constant temperature differences or if the wireless sensors are attached to equipment that always has some vibration, a small generator can use that to provide enough current to power the sensor and transmitter.”
Though wireless networks may make a lot of sense in many high reliability environments, they won’t make wires disappear. The many applications that require real time communications won’t be able to benefit from the capabilities of wireless networks. Determinism isn’t a part of these self healing architectures.
“You can’t tell how long signals will take to arrive because you don’t know how they’ll be routed,” Spohr says. “You can’t assure that signals will go from A to B, they may go from A to F to C to B.”
Wired networks will dominate in this environment. When fault tolerance is mandatory, clever engineers will have to figure out how to route cables so all paths aren’t likely to fail.
In both wired and wireless networks, the continued need for more speed shows no sign of scaling back. The volume of data carried over networks continues to rise, so bandwidth has to increase to keep up. “To maintain today’s reactions times while we’re using larger volumes of data, we need higher data rates,” Spohr says.
Ethernet’s being improved to meet those demands. As the network moves upward, it’s also going to extend its reach down to the device level. These applications typically have higher reliability requirements and lower demands for bandwidth.
In another aspect of the network’s evolution, Ethernet topologies have advanced over the years. Ethernet was originally implemented in a line topology, with multiple devices sharing a single cable. In such a topology, any cable break or fault disrupts communications for all devices. A step up in terms of reliability is the star topology, in which devices link point-to-point with a central hub or switch. For larger networks, multiple stars are configured in a hierarchical fashion, also known as a tree topology, with segments continually feeding up in the pyramid.
In either, the effect of any failure is limited to a single network segment. Industrial Ethernet takes the topology picture up yet another notch, using a ring topology to further protect against failure. Any single device failure effects only that device and any others connected directly to it. And if the cable itself should break, traffic can be routed around the break in the opposite direction to its destination. In short, with a ring topology, no single point of failure can cause a loss of network communication.
Engineers who have been managing field bus and serial networks for years understand how networks operate. While they will have to learn about the specifics of Industrial Ethernet, the technology is no more complex than what they already know. They can also use their familiar automation engineering tools to configure their Ethernet networks. And given that Ethernet has a well-defined future growth path, the knowledge they acquire will serve them well for years to come.
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