Ethernet explained. For various industries. The Independent Solution Provider for Industrial and Process Automation, Quality & IT

The Independent Solution Provider for Industrial and Process Automation, Quality & IT ATS MES Excellence Centres Ethernet explained For various ind...
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The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS MES Excellence Centres

Ethernet explained

For various industries

www.ats-global.com

Ethernet explained

The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS White Paper

Ethernet Explained Have you ever overheard a conversation between an Englishman and a Frenchman who don’t speak each other’s language? Exactly, this is almost impossible. This is not different in the world of industrial communication.

industrial computing platforms – from intelligent sensors to plant-wide supervisory control systems (such as SCADA and other systems). Ethernet owes its popularity partly to its longevity. It has been around for 30 years, it is the most common network protocol available, and most engineers these days are familiar with it. It is a worldwide standard, software is abundant and shared, and low-cost Ethernet products are widely available. Ethernet also offers a range of technical advantages. It is fast and due to its extensive error correction mechanisms, it is considerably robust, even in harsh operating environments. It also offers reasonably good security through available encryption mechanisms. Standards

This White Paper explains how Industrial Ethernet brings together the various communication protocols in the Automation Industry, and considerations when applying Industrial Ethernet. Like other off-the-shelf technologies, Ethernet has become widely accepted in the world of industrial, process and office automation. Understanding the basics is key to effective implementation. Ethernet was born in 1973 when Xerox’s Bob Metcalfe sketched the basic concept on a napkin now archived at Xerox’s Palo Alto Research Center. Originally designed for interoffice communications, Ethernet’s performance and applications have expanded considerably in recent years, especially in the industrial production and processing environment. The original standard operated at 2.94 Mbps (megabits per second). After Xerox partnered with Intel and Digital Equipment to develop the DIX 2.0 standard, Ethernet ran at 10 Mbps over thick coaxial cable. During the same time frame, the Institute of Electrical and Electronic Engineers (IEEE) started working on what is the current Ethernet standard known as CSMA/CD 802.3. In 1983, work by this group was finalized, and the standard was adopted. More recently, Ethernet has migrated to the factory floor, where more than 300 protocols are available for exchanging data among a variety of

So how does Ethernet manage to maximize the flow of data through a shared medium while keeping all the devices connected to the network from interrupting each other? It all depends on the IEEE standard for carrier sense, multiple access, and collision detection that regulates when and how data packets can be transmitted by one device and received by another. Carrier sense describes the mechanism by which a device connected to the network checks to see if another device is already communicating. Multiple access means that all devices have access to the network to communicate as long as no other device is transmitting. Collision detection ensures that when multiple devices transmit simultaneously, the collisions are detected, and the corrupted Ethernet packets are discarded. The devices then wait different time intervals to retransmit. But simply transmitting bits from one device to another is not enough to establish comprehensible communications. All that information must be organised in a hierarchical manner, much like letters must be organised into words, words into sentences, and sentences into paragraphs, to convey a written message. Ethernet-based communication protocols generally do so according to the Open System Interconnection (OSI) reference model, sometimes called the “Seven-Layer Model” (see graphic below). This model represents an ISO standard for worldwide communications that defines a framework for implementing protocols in seven layers.

www.ats-global.com ATS International B.V. © 2010 The information in this document is the property of ATS International B.V. and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of ATS International B.V.

Ethernet explained

The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS White Paper

communications. Network traffic patterns are monitored and mirrored on a diagnostic port to troubleshoot problems and determine packet types. Each port can be enabled or disabled at half or full duplex, communication speed can be set, and flow control methods established. 1. A gateway is a device for interconnecting two or more dissimilar networks. It can translate all protocol levels from the physical layer up through the applications layer of the OSI model and can, therefore, interconnect entities that differ in all details.

It defines what a transmitting device must do to pack up a message for transmission and what the receiving device must do to unpack the transmission to recreate the original message. Network device The components common to most networks are hubs, switches, gateways, and routers. Ethernet allows only one sender and one receiver at each end of a cable segment. Hubs allow the network to branch and include more devices. Hubs are used to add devices, regenerate Ethernet packets, and extend network distances. Ethernet packets that are received by a hub are broadcast to all of its ports, simultaneously and indiscriminately. Switches filter and regenerate Ethernet packets to allow for greater network distances and more devices to be connected. Most switches segment the network at the data link layer into collision domains by sending data only to the desired destination. Each switch has an addressing table listing the address of each connected device. When a packet is received, the switch stores and compares it to the address table, then forwards it to the correct port. This limits traffic on the other ports. Managed switches were developed to give network managers control over network

2. Routers divide networks into subnets by filtering network traffic by IP address. When networks are logically instead of physically divided (as with switches), only IP addresses destined for appropriate devices can pass through. If a packet is going to the immediate segment, the packet will be forwarded. If it is destined for a different segment or router, it will be tagged with appropriate information and sent on. Routing occurs at the network layer. 3. An additional benefit of a router is its ability to block broadcast and corrupted packets, which greatly reduces network traffic on subnet. Industrialising Ethernet The Ethernet developed for industrial applications follows the same constructs as the commercial Ethernet used for interoffice communications, and it uses the same OSI model. However, the two differ in the robustness of the equipment used. Light industrial Ethernet products are designed for environments harsher than the office. They feature mounting hardware to make components physically secure in standard industrial enclosures and wide-range power input options that eliminate costly wall-mount transformers. Redundant power sources add protection, and operating temperature ratings of 0-60 C guard against premature failure. Common certifications for light industrial Ethernet products include Class 1, Div. 2, shock, freefall, and vibration ratings. Testing for electromagnetic interference (EMI) and radio frequency interference (RFI) minimizes data corruption from welders and radios. For heavy industrial environments, Ethernet products must be hardened and extremely

www.ats-global.com ATS International B.V. © 2010 The information in this document is the property of ATS International B.V. and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of ATS International B.V.

Ethernet explained

The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS White Paper

rugged. In many cases they are installed in outdoor environments or on the plant floor. They must be built to withstand power surges, ultrawide temperature ranges of – 40 C to 80 C, high humidity, unstable power sources, and exposure to chemicals and corrosive materials. In these applications, explosive atmospheres, contact with liquids, and radiation also threaten the safety of equipment and people. This requires more constraints on enclosure design. High levels of EMI/RFI may require copper cage housing construction. The extreme levels of shock and vibration in heavy industrial settings require close attention to mechanical integrity and shock testing. Connecting the Plant Floor to the Office The further development of the original “office” Ethernet to live up to industrial standards has been highly advantageous for process improvements, not only on the plant floor but also on a business level. Once Ethernet rapidly transfers the right data between factory devices and is able to send this data to the right people in the organisation in the right format, it suddenly becomes more than data, it becomes valuable business information. Managers are able to make better decisions because accurate en reliable production and process information is now presented to them which can be easily reported with a software tool of choice. Once the data is sent to and from the machines and production lines inside a plant (and even between plants) through hubs, gateways, switches and routers, the only thing left to do is connect this network to the office LAN and the possibilities become endless. Talking to the Machine Although Ethernet communicates following standards and can manage data between controllers, machines, plants and lines, it is still required to actually “talk” to the machine and its controller (such as a PLC system), with their hundreds of manufacturers. One of the most widely accepted technologies nowadays to capture the data from the machine controller is OPC (OLE for Process Control). OPC follows the Object Linking and Embedding principles. This basically means translating the machine / device

language from the factory devices (such as machines, robots, etc) themselves into a standard language, similar to how Ethernet manages the information between the devices. OPC servers are available in hundreds, if not thousands of different protocols and are available at very low cost. Wireless Ethernet Whilst most manufacturing plants these days still use cabled Ethernet solutions, the acceptance of Wireless technologies is growing. Changing to wireless offers huge cost savings and physical advantages compared to cables, especially for long distance communication, obstacles (such as buildings, walls, rivers, etc.) and for instance moving applications. Imagine the cost saving if in any given application kilometres of cable needs to be purchased (let alone the cost of breaking open strips of concrete and digging tunnels for cabling), and two wireless Ethernet radios would do the same job.

Wireless Ethernet has been developed for applications in an environment unsuitable for a wired solution, such as this mining site. But similar to the difference in requirements between office Ethernet and Industrial Ethernet, standard domestic and office wireless solutions (like Bluetooth) operate in very different environments than a wireless solution in the often rugged and harsh industrial environments. Therefore, wireless Ethernet for the industry ought to be developed following the UL Class 1 Div 2 classifications for hazardous locations and the TKIP, MIC and EAP security standards.

www.ats-global.com ATS International B.V. © 2010 The information in this document is the property of ATS International B.V. and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of ATS International B.V.

Ethernet explained

The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS White Paper

Although wireless has been fully accepted for domestic and office use, applying this to industrial situations, where parts are produced and machines cannot be stopped, raises a number of questions. A further ATS White Paper is available fully dedicated to wireless Ethernet solutions and its considerations. Cables One major advantage of Ethernet is that it uses a structured cabling system that supports a multiproduct, multi-vendor environment, a major advantage over proprietary solutions. The EIA/TIA-568 standards for structured cabling, developed by the Electronic Industries Alliance and Telecommunications Industries Association, specify such details as the maximum allowable horizontal copper run (90 meters), maximum patch cord length (5 meters), and the minimum copper wire bend radius (four times the diameter of the cable). Additional standards (such as temperature, humidity, etc.) apply to networks that are to function in a harsh industrial environment, including a new connector type currently being defined by the EIA/TIA. It contains at its core the familiar 8-pin modular plug and connector.

adopting these networks but our advice is to be cautious in adopting proprietary systems. Even though there are industry support groups for the different Ethernet protocols they do limit your choice of suppliers and the different networks may be incompatible. Take advice and do your homework before making a decision as implementation costs will be much higher with proprietary solutions and the technical advantages are often vague and unclear. Security An important subject in it’s own right and we have a separate whitepaper on this subject. Designing a secure system is a combination of hardware, software and policy. Protecting your Ethernet network is addressed in our IT Security Whitepaper Summary The trend is clear for many years to come and Ethernet is the protocol standard for industrial applications. ATS and many other companies can provide expert advice on how to implement robust and secure Industrial Ethernet. Understanding Ethernet and its many potential applications will help the reader to design a robust and secure network.

The Pitfall when Industrialising Ethernet Most major industrial automation companies have introduced their own versions of industrialised Ethernet. There are some technical advantages in

www.ats-global.com ATS International B.V. © 2010 The information in this document is the property of ATS International B.V. and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of ATS International B.V.

Ethernet explained

The Independent Solution Provider for Industrial and Process Automation, Quality & IT

ATS White Paper

About ATS ATS is an Independent Solution Provider, with over 20 years experience and a wealth of experience undertaking Continuous Improvement initiatives and Manufacturing IT solution design, deployments and 24/7 support assignments.

www.ats-global.com ATS International B.V. © 2010 The information in this document is the property of ATS International B.V. and may not be copied, or communicated to a third party, or used, for any purpose other than that for which it is supplied without the express written consent of ATS International B.V.

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