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Is 100Mbit Industrial Ethernet sufficient for Industry 4.0?

Is 100Mbit Industrial Ethernet sufficient for Industry 4.0?

As we embark on the journey to Industry 4.0, it is becoming apparent that industry’s reluctance to move beyond 100Mbit Ethernet technology is a very real limiting factor. John Browett of CLPA argues that the transition to gigabit Ethernet networking technologies has to start now.

Any Industry 4.0 is going to be built on data, and lots of it. Making the best use of all this data without its volume crippling the very systems that we are using to derive value from it, will depend both on speed and bandwidth. And whatever bandwidth we believe to be adequate for today’s requirements, in the future we’re going to need much more of it.

There are those who argue that the speed and bandwidth debate is irrelevant, and that with the adoption of technologies such as OPC UA and TSN, bandwidth is just something we’ll be able to take for granted. But while they clearly have an important role to play, these are complementary technologies, not replacements for existing networking protocols. Network bandwidth in industrial applications is a debate we need to be having right now if we are to prepare ourselves for life in the factories of the future.

We may not know exactly what these future network infrastructures will look like, but we can already see some clues in cloud computing. The information throughput in most of today’s industrial processes is some way off being regarded as ‘big data’, but it’s a lot of information nonetheless. Right now, the information being sent to the cloud is, by and large, information for historical logging and trend analysis, separated from the real time control data by using the likes of edge computing platforms. But if the predictions of some companies are correct, then edge computing is just an intermediate step, and we could soon see the likes of virtual PLCs and virtual SCADA in the cloud, collecting data from and sending it to plant floor devices in real time.

If that picture of the future comes to pass, it will certainly need high speed networking technologies as a prerequisite. But even today, looking at the data we are trying to pour through our edge computing platforms, the standard 100Mbit technologies are surely feeling the strain. We might not have felt that yet, because modern industrial Ethernet protocols are implemented to avoid collisions, so that OT performance is not impacted.

But imagine a network that is transmitting both synchronous control information (I/O states, data registers, etc.) and asynchronous information such as alarms, quality data and other messages. A machine jam or a parameter drifting out of tolerance or any number of process glitches could see the network flooded with alarm messages, which can quickly impact on the performance of the whole system.

Let’s consider some analysis of how much additional capacity gigabit bandwidth offers: in broad terms the throughput offered by 1Gbit Ethernet is 10x greater than 100Mbit Ethernet, however, there is also the data packaging to consider. Ethernet frame format, type II frames include: Preamble (8 Bytes); Interframe gap (12 Bytes); Destination MAC (6 Bytes); Source MAC (6 Bytes); Protocol Type (2 Bytes); Payload (minimum 46 Bytes, maximum 1,500 Bytes – includes Network Data and any additional Ethernet headers); and CRC (4 Bytes).

In some Ethernet uses, additional overhead is necessary and part of the Payload which reduces the Network Data size. With no additional Ethernet overhead, Payload and Network Data are equivalent.

With a Payload size at the minimum of 46 bytes and using Ethernet Frame format, type II (no other overhead):

  • Gigabit Ethernet has a throughput of 1,488,095 frames/s and can transmit a maximum of 68,452,370 Network Data bytes in 1 second.
  • 100Mbit Ethernet has a throughput of 148,809 frames/s and can transmit a maximum of 6,845,214 Network Data bytes in 1 second.

With a Payload size at the maximum of 1500 bytes and using Ethernet Frame format, type II (no other overhead):

  • Gigabit Ethernet has a throughput of 81,274 frames/s and can transmit a maximum of 121,911,000 Network Data bytes in 1 second.
  • 100Mbit Ethernet has a throughput of 8,127 frames/s and can transmit a maximum of 12,190,500 Network Data bytes in 1 second.

What this means is that devices on gigabit Ethernet networks can send more messages. Because each message occupies the network for less time, more messages can be sent without impacting the network. We’re not talking about problems with collisions, because in general industrial Ethernet networks take care of that through other methods. Rather, it is all about how much useful data can be collected and used from each message. All of which has implications for the quality of the production decisions that are being made at the enterprise level.

Detractors of gigabit Ethernet ask if the speed of transmission matters. The speed of transmission does matter because this allows for more messages per cycle and thus more useful data collected. Even with a limit on the amount of data per device, this does not imply a limit on the data collected because data registers can be constantly changing. Hence as Industry 4.0 requires us to extract more and more useful information from our production systems, gigabit Ethernet offers the ability to provide the speed and bandwidth necessary to do this.

If we look at CC-link IE Field, not only does it have 1Gbit transmission speed, it also has a greater Network Data capacity than both TCP/IP and UDP/IP General Purpose Ethernet. This is due to the additional overhead required for the IP, TCP and UDP headers used by General Purpose Ethernet frames. These additional headers used for General Purpose Ethernet frames are placed within the Payload portion of the frame. This reduces the Network Data that can be transmitted by each Ethernet frame. In CC Link IE Field transmissions, no additional Ethernet header(s) are required, thus Network Data is not reduced.

Hence when compared to general purpose Ethernet networks, at gigabit speeds and depending on payload, CC-Link IE Field has the ability to offer better than 660% bytes per second performance increase over TCP/IP, and better than 150% increase over UDP/IP when transmitting with a minimum payload.

For those who still need convincing that we are heading towards a gigabit Ethernet future, it is interesting to consider the companies making industrial Ethernet switches: looking at their product portfolios reveals growing numbers of gigabit Ethernet products. If we are to realise the goals of Industry 4.0, then we have to conclude that gigabit Ethernet isn’t simply a conceptual future; it’s a very real present.

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