EtherNet/IP versus PROFINET
PROFINET and PROFIBUS communications are deterministic, which allows support of automation systems with precise I/O structure limits and their defined I/O structures allow precise calculation of maximum update times. PROFINET can also provide isochronous real- time (IRT) data exchange. IRT essentially leverages the ultra- precise time clock of PROFINET to prioritize the passage of some types of data traffic and buffer the rest. IRT excels in demanding applications such as motion control and other applications that need more deterministic operation than real-time operation. In a real-time data exchange, bus cycle times are less than 10 msec. In contrast, IRT data exchanges occur within a few dozen μsec to a few msec. For example, PROFINET in a packaging and labeling operation can support data transmission to ensure bottles are filled to a precise level in less than a second — to within just an msec or so. PROFINET can also detect, quantify, and alert operators of any anomalies in the bottling process and immediately shutdown processes as well. Side note on PROFINET hardware Standard Ethernet is only suitable for data transmission in home, office, and select industrial-monitoring settings. In
contrast, the industrial Ethernet of PROFINET is suitable for installation in harsh industrial facilities requiring deterministic data communications. PROFINET cables and connectors differ from those employed in standard Ethernet — and includes connectors with heavier lock mechanisms and ruggedized industry cables. PROFINET routers (whether integrated into other hardware or built as standalone elements) function on network layer three (from the network models mentioned earlier) and communicate using IP addresses. These routers connect local area networks (LANs) and form wide area networks (WANs) while employing algorithms to determine the best data-transmission routes between networks. Some PROFINET switches also employ fiber-optic connections. These ultra-fast components integrate PROFINET-capable devices into Ethernet networks (or PROFIBUS) via gateway elements for copper- to-fiber-optic conversions. PROFINET managed and unmanaged switches PROFINET switches work on the second data layer of the conceptual network model covered earlier. They function to control the receipt and transmission of data signals through the network. Unmanaged PROFINET switches send incoming Ethernet data through the proper ports connected
Data transmission via EtherNet/IP
PROFINET for deterministic communications PROFINET is another technical standard that defines a mode of data communication via industrial Ethernet. PROFINET modifications to standard Ethernet ensure proper and prompt data transmission even in challenging applications. Its definitions dictate a means of data collection from industrial equipment and systems to satisfy specific and often tight time constraints. PROFINET arose from PROFIBUS — a standard for fieldbus communication to support automation. While PROFIBUS is a classical serial fieldbus based on industrial Ethernet, PROFINET goes further with additional capabilities to allow faster and flexible communications to control automation components. In fact, PROFINET had 30% of the industrial-network market share as of 2018, making it the world’s leading Ethernet-based communication solution for industrial automation. More than five million PROFINET-ready devices come to market every year.
Figure 2: Because EtherNet/IP works on the application layer, it allows communications between industrial controllers and I/Os. NT24k switch image source: Red Lion
TCP and the user datagram protocol (UDP) are the underlying communication protocols of the Internet and many private networks as well. EtherNet/IP employs a TCP port for what is called explicit messaging. Such messaging is when the system sends data to a client in response to a specific request for that data. It uses TCP/IP — a connection-oriented protocol that explicitly manages links between clients and servers. Core to TCP/IP networking, TCP helps fragment data packets so that data messages reach their destination. Note that IP deals only with packets; TCP lets two hosts establish connection and exchange data streams. TCP guarantees delivery of data as well as that packets will be delivered in the order in which they were sent. EtherNet/IP employs a UDP port for implicit messaging — system communications sent from preset memory locations to a controller or other client at some prescheduled interval. Such communications are far faster than explicit messaging, and the one-way data transmission of UDP connections (sans validating receipts) simplifies cyclical system updates.
At present, EtherNet/IP is one of four ODVA networks that have adopted CIP for industrial networks. The others are DeviceNet, ControlNet, and CompoNet. CIP is a conduit of organizing and sharing data in industrial devices. More specifically, it uses different types of messages and services to exchange data in industrial automation applications that include process and system control, safety, synchronization, motion, configuration, and information. CIP lets these applications integrate with enterprise-level Ethernet networks and the Internet. It is a unified communication network used for manufacturing and industrial applications and widely adopted by vendors around the world. For industrial protocols, data is ordered as objects with data elements or attributes. These data objects typically sort into required objects and application objects. The former are found in every CIP.
EtherNet/IP is rather easy to implement, and it’s compatible with standard Ethernet switches for industrial automation. However, the basic form of EtherNet/IP is non-deterministic and therefore unsuitable for strict real-time industrial applications. CIP Motion can complement EtherNet/IP to help the latter satisfy demanding requirements for deterministic real- time control (including closed-loop motion control) with unmodified Ethernet in full compliance with IEEE 802.3 and TCP/IP Ethernet standards. EtherNet/IP complemented with CIP Motion technology delivers multi-axis distributed motion control. It is scalable and offers a common application interface for motion designs.
Figure 4: EtherNet/IP is most common in the United States. PROFINET is widely used in Europe. Image source: PI North America
Figure 3: EtherNet/IP and PROFINET are leading industrial Ethernet protocols. Both are supported by the ODVA. Image source: ODVA Inc.
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