TECHNICAL ARTICLE | Share on Twitter | Share on LinkedIn | Email Ethernet in the Automation Industry Part 3: Modbus TCP and PROFINET In the first part of this series, we examined Ethernet’s numerous advan- of EtherNet/IP, Modbus TCP, and some forms of PROFINET all allow for this tages over fieldbuses within industrial automation and control. Ethernet level of interaction through CPwE. Ethernet, IP, and TCP/UDP can be used solutions offer superior bandwidth and lower equipment costs, as well at layers 2, 3, and 4, respectively, for communications between network as the ability to be extended across the entire plant as single networks devices running standard protocols. linking the factory floor with enterprise IT. With that third characteristic in mind, we also began, in the second part, to delve into converged Modbus TCP and PROFINET for Interoperable and plant-wide Ethernet (CPwE), the reference architecture jointly developed Interconnected Networks by Rockwell Automation and Cisco to encourage the modernization of IAC Let’s look at the two Ethernet-based solutions—Modbus TCP and a few 1 systems through the use of standard Ethernet in tandem with the IP suite. versions of PROFINET—that can interact with EtherNet/IP and other protocols (for example, HTTP, FTP, Telnet, etc.) without requiring the CPwE Overview and Wrap-Up implementation of nonstandard network interface cards and/or switch- CPwE is, at its heart, an attempt to help manufacturers move past the ing infrastructure. Both of these standards are popular, with PROFINET complexity of disparate legacy serial networks and achieve the service accounting for 8% of all industrial networks as of January 2015, and integration, straightforward maintenance, and high availability that they Modbus TCP holds 3% of the same market. need to prime their plants for use cases, such as the Industrial Internet of Things. By bringing IT and control engineers—and the respective systems Modbus TCP they oversee—under the same tent, CPwE ideally optimizes industrial Modbus TCP is a variant of the widely used, vendor-neutral Modbus operations to make the most of raw materials and ensure on-time product protocol that was originally introduced by Schneider Electric in 1979. and service delivery. Where Modbus utilizes serial connections, Modbus TCP uses Ethernet as ® its physical network, with support for the TCP/IP stack for data exchange EtherNet/IP has been the primary vehicle for CPwE, since it serves as a over IP networks. Modbus TCP was standardized in 1999 and can now ( link between Cisco’s Ethernet-to-the-factory framework which includes be implemented on any device with TCP/IP sockets.3 security and network architectures) and Rockwell Automation’s integrated architecture with its Logix Control and FactoryTalk platforms. Industrial The open, standardized design of Modbus TCP makes it an excellent Ethernet switches within CPwE implementations have common industrial choice for interoperable environments. It can be run using regular PC protocol integration via their native EtherNet/IP support. Ethernet cards, plus it is future-proof as a result of having Ethernet port 502 specifically assigned to it. Now managed by the Modbus Organization EtherNet/IP uses standard, unmodified Ethernet technologies to enable (since 2004), following its initial development by Schneider, Modbus is this comprehensive end-to-end network integration that is unachievable an open project with a broad vendor community working on increasingly through purpose-built fieldbuses. The Cisco-Rockwell partnership has cost-effective solutions. also streamlined overall CPwE implementation through support for WLANs The use of TCP/IP, rather than UDP, enables a large number of concurrent predicated on IEEE 802.11 Wi-Fi. These WLANs have granular quality of connections in Modbus TCP, along with low maintenance control of data service and traffic prioritization features to help overcome the interference transactions. In this way, Modbus TCP diverges from the stateless transac- 2 and coverage impairments that often beset industrial wireless networks. tions of its Modbus family predecessors and emulates the minimalism of The standards-based designs of EtherNet/IP, Modbus® TCP, and some the World Wide Web. forms of PROFINET® allow for interaction through CPwE. “The main reason [for using TCP/IP in Modbus TCP] is to keep control This time around we will look beyond EtherNet/IP at other industrial of an individual ‘transaction’ by enclosing it in a connection which can Ethernet protocols that support standard networking to one degree or be identified, supervised, and canceled without requiring specific action another. After all, part of CPwE’s value proposition is the ability to facilitate on the part of the client and server applications,” explained a real-time automation guide to Modbus TCP4. “This gives the mechanism a wide interconnectivity and interoperability between IAC networks that commu- tolerance to network performance changes, and allows security features nicate mostly within a layer 2 LAN model. The standards-based designs such as firewalls and proxies to be easily added.” Visit analog.com PROFINET References Having covered PROFINET in several other entries here,5 we won’t do a 1 “Converged Plantwide Ethernet (CPwE) Design and Implementation deep dive into all of the protocol’s features. However, it is worth noting Guide.” Cisco Inc. that its design—with support for standard TCP/IP, as well as a special 2 stack that bypasses TCP/IP for transmission of real-time data in PROFINET “Deploying 802.11 Wireless LAN Technology within a Converged I/O and IRT—is particularly amenable to balancing the convenience of Plantwide Ethernet Architecture.” Cisco, Inc., November, 2014. office Ethernet with the demands of industrial networking. 3 Modbus FAQ: About the Modbus Organization Like Modbus TCP, PROFINET is mainly used for industrial automation 4 Modbus TCP/IP Unplugged—An introduction to Modbus TCP/IP process control. Its support for streamlined cabling (for example, through Addressing, Function Codes and Modbus TCP/IP Networking. Siemens’ FastConnect system), deterministic performance over WLAN, and RTA Automation. compatibility with star, tree, and ring topologies (in addition to the linear layouts of fieldbuses) have made it a popular choice for simplifying the 5 “From PROFIBUS to PROFINET, Part 2.” Analog Devices, Inc., layout and boosting the performance of modern IAC systems.6 Moreover, March, 2015. the ability to easily transition from PROFIBUS—the most popular fieldbus 6 Advantage with PROFINET. Siemens. and industrial network in current use—makes PROFINET integration an easy decision for many manufacturers. PROFINET, Modbus TCP, and EtherNet/IP are all good examples of how Online Support ubiquitous technologies such as Ethernet can be used as the basis for Community exacting, scalable, and industrial automation. The benefits of Ethernet in Engage with the factories have always been its familiarity and flexibility—it can unify the Analog Devices technology experts in our online support industrial and offices networks while going beyond fieldbuses in key areas community. Ask your tough design questions, browse FAQs, such as bandwidth and straightforward support for TCP/IP. Architectures or join a conversation. like CPwE and the ongoing development of projects such as time sensi- tive networking (TSN) will only extend Ethernet’s reach in the automation Visit ez.analog.com industry in the years ahead and contribute to more efficient plants both now and in the future. Analog Devices, Inc. Analog Devices, Inc. Analog Devices, Inc. Analog Devices, Inc. ©2017 Analog Devices, Inc. All rights reserved. Trademarks and Worldwide Headquarters Europe Headquarters Japan Headquarters Asia Pacific Headquarters registered trademarks are the property of their respective owners. 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