Comparing the performance differences between business and industrial applications reveals that the packet rate, packet size and bandwidth utilization of industrial applications exhibit characteristics opposite those of business applications. (Table 1)

Graphing test application packet captures for both industrial and business edge devices illustrates the difference. In Figures 1 and 2, the business application trend is in black and the automation application trend is in red.

Business applications have packet burst rate requirements that define the upper limit bandwidth requirement of the infrastructure. With multiple users sending packet bursts, 100 Mbs from the edge to the core can easily be saturated. The data volume represents the larger packet sizes used by business, for example when loading Web pages or network printing.

Industrial applications on the other hand, have a higher, steady-state packet rate with lower overall data volume due to the much smaller packet size as shown in Figures 3 and 4. Industrial Ethernet packet sizes are typically less than 500 bytes. The smaller packets interleave more effectively than larger packets and therefore reduce the likelihood of congestion.

Since most industrial Ethernet applications use cyclic, steady-state communications, packet bursts are rare. Coupling the packet sizes and packet rates together reveals the average bandwidth utilization in our five-minute test capture. As you can see from Figure 5, the overall utilization is under two Mbs, typical for many industrial Ethernet applications. Though some may express concern about the high volume of communications in industrial Ethernet, the reality is that 100 Mbs full duplex Ethernet is quite sufficient for most applications.

For business applications, applying increased bandwidth generally yields better performance. For industrial Ethernet applications, additional bandwidth has little effect. Most automation edge devices do not have the processing speed and memory of business desktop PCs and servers. The key factors for industrial applications are efficiency and reliability. Environmental Factors
Business infrastructure Ethernet switches typically are installed in temperature-, air quality- and humidity-controlled areas with filtered power, standard surge suppressed outlets, and Uninterruptible Power Supply (UPS) backup in the event of a power failure. There is less consideration for power redundancy in terms of dual power supplies or separate feeds for edge switches. Core switches are more likely to be equipped with redundant power supplies and this is reflected in the premium price of the core business switch.

Business Ethernet switch devices are equipped with fans to cool the switch mother board. Should moisture or dust accumulate on the system board, the board could overheat and fail.

Since the stackable edge switches are designed to typically accommodate 24-48 ports, should an edge switch fail due to environmental factors, the impact to the business is localized affecting only those users attached. Moreover, due to the cost considerations, redundant power is excluded in many business edge switch offers due to the relatively localized user impact.

Since the switch stacks at the edge of the IDF employ standard plug grounding, and office installation cable trays bypass electromagnetic and radio frequency interference systems such as HVAC and fluorescent lighting ballasts, there is less consideration for using shielded horizontal cabling by appropriately choosing cable tray routes. Subsequently, this reduces media costs and can lower the overall project costs when deploying or locating IDF closets.

Business systems also are conditioned to replace edge switch equipment on 3-5 year intervals to accommodate the evolution of the technology and the new service demands, both required and anticipated This has led business Ethernet switch offers to give up Mean Time Between Failure (MTBF), in favor of providing yet higher bandwidth to the desktop edge and having customers upgrade on a regular basis.

Industrial Ethernet systems on the other hand, often require operation in harsh environments. Fans that can draw in dust and cause the failure of a mother board can threaten premature failure at an inconvenient time with substantial associated costs. For this reason, convection cooling without the use of fans is widely preferred by industrial Ethernet switch OEM's.

Industrial systems also are designed for minimal upkeep. Excluding any potential environmental factor that could threaten product yields, such as temperature, dust, debris or humidity, the cost savings measured far outweigh the cost of the switch itself. Industrial Ethernet switch OEMs have responded by testing and certifying their product offers to survive these environments with long MTBF cycles.

Electromagnetic and radio frequency devices are common in industrial environments. Employing support of shielded media and positive grounding leads not only to the protection of the Ethernet switch and end devices, it also reduces the risk that an Ethernet packet will be corrupted during transit. The integrity of each packet is critically important to prevent delay as well as to rely on higher layer protocols such as TCP to manage retransmission and error recovery mechanisms.

Configuration and Maintenance
Businesses have highly evolved help desk and network operations support systems for configuring, managing and maintaining the network. Problem reports typically are dispatched through a call center, which prioritizes each request and assigns it to the appropriate group or individual. Often these individuals are sharing their time with projects related to deployment or roll-outs, learning a new application, or endeavoring to support it.

Sometimes requests for help are prioritized by the individual or department requesting it. Network personnel may respond to requests more toward the political hierarchy than the bottom line business impact.

Help desk personnel are well trained in business applications and maintaining network edge switches. Should the assistance required escalate to the network team, further resources are available. However, the network team's goals often are driven by factors unrelated to manufacturing and production processes. It is possible then, that a request to service an industrial Ethernet production device may end up near the bottom of the priority list.

Industrial Ethernet applications require immediate assistance should an Ethernet device or switch experience a problem. Any impact to production can quickly drive up expenses, production schedules and opportunity costs. Having help desk personnel delay response to a production problem that impacts the bottom line of the business is a risk. Additionally, if help desk personnel are unfamiliar with automation applications, more costly mistakes can occur.

As there is sometimes little cross-training or cohesion between the industrial Ethernet and business/IT groups, simple tools to resolve network and device issues fall to the maintenance department. Industrial Ethernet switch OEMs have developed simple tools, methods and interfaces to allow the maintenance person to resolve the problem.

Features such as Web interfaces that simplify the configuration options, or allow discovery and primary configuration of a switch by simply powering it up and plugging into the network, help maintenance personnel deploy an industrial Ethernet infrastructure with little or no reliance on the help desk. In the event of a device failure, fast replacement is essential for industrial applications. Industrial Ethernet OEMs have developed simple methods for replacing a device, in some cases with only a screwdriver to match settings on rotary switches. Signal interfaces can also help alert maintenance personnel to problems on the network. Industrial Ethernet switch signal interfaces can be wired directly to PLC or I/O modules and monitored for errors in logic. Should an error occur, this can be reported to an operator via an HMI console.

Conclusion

As industrial Ethernet continues to evolve and mesh with the traditional business Ethernet environment, controls engineering will find it essential to partner with the IT department to determine complementary technical solutions and cross train personnel to support the industrial applications.

Engineers also should recognize the importance of Ethernet infrastructure devices suited to the task and that the corporate standard is not necessarily best solution for an industrial environment.

About the Author

Michael B. Roche, principal technical marketing specialist, Schneider Electric Services, Schneider Electric North American Operating Division