Industrial Ethernet protocols and time-sensitive networking

Quick hits:

  • Learn how time-sensitive networking brings determinism to Industrial Ethernet.
  • Understand why Time-Sensitive Networking is only concerned with data transfer in the OSI model.
  • How industrial Ethernet protocols address applications, the higher levels of the OSI model.

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Read the transcript below:

Welcome to Take Five with Automation World. I’m David Greenfield, Director of Content, and today we’re going to look at why Industrial Ethernet protocols are still needed with time-sensitive networks.

But first, to make sure everyone is on the same page, let’s start by explaining Time-Sensitive Networking or TSN. Essentially, TSN is a way to provide determinism over Ethernet. And the lack of determinism in standard Ethernet has always been one of the main drawbacks of using Ethernet as a factory network. But since determinism is largely only required for high-speed or high-accuracy control applications, Ethernet has slowly but surely gained traction in manufacturing and process facilities over the past two decades across all industries. other areas of operation. In areas where determinism is needed, deterministic fieldbus technologies have largely remained in place.

The reason Ethernet lacks determinism is the way it handles the information packets it carries. When multiple devices communicate over a network, which is typical of any business network, Ethernet avoids data collisions, which occur when multiple data packets are sent at the same time, by withholding certain packets of information while d others pass. This avoids the potential loss of information when packets are dropped, for example during a collision.

Of course, this is a very simplistic explanation of how Ethernet handles data transmission without getting into the roles of routers, switches, and MAC and IP addresses. But hopefully it will get over the idea that some data packets can be withheld while others pass. For most information packets, this is not a problem. For example, if it takes you a split second longer to receive your email, not only will it not impact your operations, you won’t even notice it. But this type of delay can cause problems with high-speed, high-precision machines.

This is where TSN comes in. TSN is an IEEE 802.1 standard originally developed for the AV industry to better synchronize audio and video. But the deterministic communication it provides can be used for Ethernet-based control traffic, because it not only ensures that critical control communications pass unhindered by other traffic on the network, but that control communications are treated with the highest priority.

The first step in understanding how Industrial Ethernet protocols work with TSN is to understand that TSN only addresses network functions at Layer 2 – the data link layer – of the Open Systems Interconnection model, often referred to as the OSI model. . Tom Burke, global strategic advisor to CC-Link Partner Association, which supports the CC-Link IE Industrial Ethernet protocol, indicates that since TSN only operates at this Layer 2 level, it is only responsible for transmitting data from one location to another in a deterministic manner without look what the data. This means that everything that needs to be done with the data transmitted via TSN is handled at the higher layers that meet the requirements of the application. That’s where industrial Ethernet protocols come in. According to Burke, the protocols and TSN work together around convergence, because most industrial Ethernet protocols don’t allow for merging different types of traffic on the same network. Thus, TSN essentially creates a system that provides the necessary flexibility by allowing multiple types of traffic to share the same network while being treated deterministically.

Now, Burke advises that for machine builders and end users to realize the full benefits of a TSN-compliant Ethernet protocol, they should carefully review its specifications to ensure that it can meet the requirements of their intended applications. . He points out that a proper protocol must encompass I/O, motion control, and security.

And Burke notes that CC-Link IE TSN is an industrial Ethernet protocol that combines Gigabit bandwidth and TSN functionality. The CC-Link IE TSN protocol uses Layers 3 through 7 of the OSI model to build on Layer 2 TSN capabilities. and security to standard TCP/IP traffic over Ethernet in a deterministic manner.

In addition to CC-Link IE TSN, other industrial Ethernet protocols that have extended their technology for use with TSN include Profinet, EtherCAT, EtherNet/IPand even SERCOS— which has long been recognized specifically for its deterministic capabilities.

So I hope you found this episode of Take 5 useful.

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