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EtherNet/IP is one of the most prevalent communications protocols used in today's industrial systems. Find out more about this application layer protocol!
For more details about the CIP-based protocols of the ODVA, visit the ODVA website: https://www.odva.org/
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AutomationDirect presents What Is – networking edition. What is EtherNet/IP? If you’re new to automation circles, haven’t yet had a chance to work with Ethernet/IP, or maybe just want to know a little more about this industrial communication protocol, watch on. Ethernet/IP is definitely worth looking into. Robust, reliable, and fast, Ethernet/IP is an application layer protocol used throughout industries worldwide, thanks in part to its adoption by some of the most prominent controls manufacturers in the business. By some estimates, it holds a 30% market share of the industrial Ethernet market and accounts for over 20 percent of all new communications implementations (Ethernet and otherwise) in factory automation globally. Ethernet/IP can be thought of as having two parts, the “Ethernet” and the “IP”. The Ethernet part refers to the traditional Ethernet technology that Ethernet/IP adapts. In other words, EIP uses the physical and software Ethernet standards provided in IEEE 802.3 for its transportation—the Transport, Network, Datalink, and Physical layers in the OSI model. This gives EIP many advantages - the ability to utilize off-the-shelf Ethernet hardware for its network, for example, and the use of standard IP addressing and subnetting. It takes advantage of both the TCP and UDP protocols that Ethernet uses. Recall that TCP is a connection-oriented protocol, and it employs handshakes and acknowledgments to ensure that a connection is intact and that the target device has received the sent packets successfully. UDP, on the other hand, uses a connectionless communication scheme in which transmissions are not acknowledged and which generally require much less overhead. We’ll return to these two different schemes in a minute and see how they relate to the types of Ethernet/IP communications. The other half of the Ethernet/IP equation is the “IP.” The potentially confusing designation does not refer to the Internet Protocol as in “IP address” but to Industrial Protocol. Specifically, Ethernet/IP is built on the Common Industrial Protocol. CIP is an object-based protocol that handles data representation, connection management, and messaging but does not incorporate its own transport and physical layers. Therefore, it can be paired with other protocols that handle the data transport. CIP paired with CAN technology is DeviceNet. ControlNet and CompoNet both use CIP with their own Transport and Physical layers. Ethernet/IP – CIP adapted to Ethernet - is by far the most widely used of these. All of these, along with CIP itself, are administered by the Open Device Vendor Association. The ODVA manages Ethernet/IP as a certifiable standard, meaning that all manufacturers and vendors implementing the technology must adhere to a declaration of conformity to maintain a license for its use. Interoperability among certified products from different vendors is assured. In EIP communications, we broadly categorize components into Originators and Targets, with the Originator being a master (like a PLC or other controller) in command of one or more Target devices - sensors or other field devices. As was mentioned before, Ethernet/IP utilizes both TCP and UDP protocols for different types of communication between Originator and Target devices. Explicit communication uses TCP in a request/response arrangement. Each message opens a point-to-point connection, with an establishing handshake, receipt acknowledgment, etc. Each message also explicitly spells out for the Target what information is being requested or sent (this object, this class, this instance, formatted precisely this way, and so on). The explicit message has a lot of overhead and carries a lot of data, so, of course, it is relatively slow. For this reason, explicit messages are sent asynchronously—only when required. They are often used to carry settings and other non-time-critical data. In Explicit messaging, the Originator is typically called the Client, and the Target is the Server. Explicit messaging uses Port 44818. Implicit messaging – sometimes called IO messaging, on the other hand, employs a constant stream of data from the Target device, called an Adapter, to the Originator, called a Scanner, transmitted via UDP. Implicit messaging fits a Producer/Consumer communication model. There are no requests and no information about what the scanner needs, no handshake checks, and no receipt acknowledgments. Since the adapter will be sending a steady, repeating stream of data, a missed message is not a significant concern since another is on the way within milliseconds. The data the Adapter sends has all been pre-configured in the Scanner – either manually or by the provision of the adapter’s Electronic Data Sheet. The EDS is a simple ASCII file that identifies all the Adapter’s data. So, the data stream’s identity is understood by both devices before communication even starts – Implicit, in other words. For these reasons, Implicit messages are lighter and much faster than Explicit. Implicit messages are considered to be “soft real-time” communication and typically contain field IO data “adapted” into communications. Implicit messaging uses Port 2222. There are many great resources out there for anyone wanting to delve more deeply into some of the topics we’ve touched on here. We hope this gives you a starting point for your exploration of the Ethernet/IP protocol. To learn more about Ethernet/IP-capable PLCs and field devices, visit AutomationDirect.com. Click here to see other videos about industrial communications. Click here to subscribe to our YouTube channel.
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