Choosing between corporate IT or Industrial Ethernet, Part 2

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.