Now that Ethernet has permeated the plant floor, end users face the challenge to adapt Ethernet for industrial applications. Commercial Ethernet offers many advantages, but there also are key issues that must be addressed for successful industrial implementations. Ethernet routers and switches that address these issues will enjoy wide acceptance and strong growth.
According to Carl Staffan Dahlstrom, executive vice president of HMS Industrial Networks (www.hms-networks.com), one of the leading problems with industrial implementations of commercial Ethernet is the star/tree topology.
Most industrial Ethernet customers don't want to use the star/tree topology that switched Ethernet provides, and many consider installations would be much more efficient with a bus/"daisy-chain" topology.
Network and user devices form the foundation for Ethernet technology. The network device is responsible for switching packets between the user devices. Communication may be single links, or multiple links trunked together for aggregated bandwidth and redundancy, but, in either case, the network is still based on a star topology.
Bus-type networks like ControlNet, DeviceNet, or Profibus allow installation of just one communication cable. Each device is then connected to this main cable via a short tap/trunk line. This is very flexible and cost efficient compared to a star topology.
A common example is a manufacturing line 200 ft. long with 50 different nodes. This installation might have a control cabinet at one end of the line with the main controller and an Ethernet port.
With Ethernet, this installation would need switches to get acceptable data update times between the PLC and each remote unit. According to Dahlstrom, an Ethernet network with switches would offer performance similar to fast fieldbus networks such as Profibus.
The problem is that switched Ethernet requires a star topology with attendant wiring requirements. "Our industrial customers tell us that some of their switched Ethernet installations resemble old hard-wired networks where each device had multiwire cable connecting it to the I/O rack of the PLC," observes Dahlstrom.
To address the topology issue, the Profibus organizations are working with the next generation of ProfiNet Ethernet networks to allow Ethernet bus/"daisy-chain" topologies for device connection on the factory floor.
This will be accomplished by integrating a four-port Ethernet switch into each end device. ProfiNet's intention is to integrate a low-cost four-port switch at each node. This would enable a combination of star and daisy chain/bus-type installations.
This solution is becoming feasible because of the low and ever-declining cost of Ethernet hardware. "Siemens is currently developing new silicon for this application. We expect it to reach the market in 2005, further lowering costs," adds Dahlstrom.
Speed and determinism are key performance metrics for industrial Ethernet applications. "We use layer-3/4 gigabit-switching devices in the core and in other critical areas of the plant networks where Ethernet determinism and high-speed is needed," says Donovan Tindill, CET, network solutions consultant for Matrikon (http://www.matrikon.com/solutions/network/). "With gigabit switching and quality of service, determinism is absolutely achievable."
Although most Ethernet switches in new industrial installations are 100 Mbit, the judicious use of 1 Gbit switches can greatly improve network performance. Brute force in terms of more speed is good, but adding intelligence to switches also can improve network performance.
The aforementioned layer-3 switching is one form of "managed" or smart switching. "SNMP or layer 3 switching will provide better administration, reduced costs, and prioritization of the data packets, which allows for better performance by offloading slow router traffic," says Kevin Allan, the director of product marketing, business products, at Netgear (http://www.netgear.com).
Market leader Cisco Systems (http://www.cisco.com) also stresses the value of smart switches through a suite of features that it calls Intelligent Services. These services break down into three categories: availability, quality of service, and security.
Availability is addressed through multicast control and redundancy. "Ethernet production networks can be very multicast-intensive because devices are sending constant streams of information into the network that other devices occasionally read. Intelligent switching filters this information from devices that did not request it, allowing them to perform better while still accessing needed data," says Larry O'Connell, product manager of the desktop switching business unit at Cisco.
Redundancy is implemented by Cisco through a rapid-spanning tree protocol designed to bring a network back on line after a link failure in less than a second.
Quality of service (QoS) is the concept of prioritizing data and allocating bandwidth for these data. "QoS provides the ability to ensure determinism by assigning a policy that prioritizes production data. A switched Ethernet network and QoS assure determinism in manufacturing environments even during periods of high network congestion," states Connell.
Speed and intelligence increase performance, but security is just as important for many applications. In manufacturing, it is desirable to keep production data logically separate from non-production data. In other words, web pages or file transfers should not mix with production control and configuration data. This is accomplished by implementing appropriate security features.
According to Connell, Cisco's intelligent switching provides the ability to secure the network on the basis of physical ports, MAC addresses (devices), IP addresses (networks), and TCP/UDP identifiers (applications). Intelligent switching allows a user to assign a policy to a production line's network that will allow only Ethernet/IP traffic and access from a few predetermined IP addresses. This keeps the network safe while allowing access for troubleshooting.
Intrusion-aware firewalls are another technology used to implement security through smart Ethernet switches and routers. "Intrusion-aware firewalls are smarter than typical firewalls," says Tindill of Matrikon. "They include intrusion detection to prevent known attacks, along with access control for mission-critical plant systems." Tindill foresees features in business-class network devices such as QoS, intrusion detection, and IPsec encryption infiltrating industrial-grade network components.
Proprietary wireless networks abound, but wireless Ethernet may supplant these proprietary technologies in the near future for many industrial applications. "Wireless products (routers, access points, and NIC cards) are increasingly becoming a significant portion of our business," comments Netgear's Allan.
"The introduction of higher-speed wireless (54/108 Mbps 802.11g and 54 Mbps 802.11a) has overcome the "boutique" stigma of earlier versions of wireless," Allan believes. "Newer security technologies such as WiFi Protected Access support are overcoming the concerns raised earlier about the security holes in standard WEP encryption."
Wireless Ethernet technologies will provide network connections to PDAs and laptops for use in warehouses and for real-time inventorying and field data collection. Wireless Ethernet also will be used by maintenance technicians to connect tablet PCs to computerized maintenance management systems.
Although many industrial applications can use commercial-grade switches and routers, in some cases it is necessary to use ruggedized industrial Ethernet hardware. In other cases it is cheaper to use industrial Ethernet hardware because such hardware often eliminates the need for the conditioned environments required by commercial components.
As Ethernet continues its fast growth, the industrial market is expected to see correspondingly fast growth in demand for industrial Ethernet hardware.
What makes Ethernet hardware rugged? "Our ruggedized products have extended operating temperature ranges, rugged metal housings, and fan-less operation. They withstand vibration and are highly immune to electromagnetic interference," says Joe Gould, senior field applications engineer with RuggedCom (http://www.ruggedcom.com).