DeviceNetâ„¢ and ControlNetâ„¢ are well-known industrial networks developed by ODVA (Open DeviceNet Suppliers Association) and ControlNet International, respectively. Both networks operate on the CIP protocol at the application layer, which is also known as the General Industrial Protocol. Recently, these two organizations have collaborated to introduce EtherNet/IP, a standard industrial Ethernet protocol. This article explores its technical principles, transport mechanisms, and how it ensures consistent network services and data objects over Ethernet using TCP/UDP/IP.
I. Introduction The network in an industrial automation system must provide three essential services: control, configuration, and data acquisition. Control is the most critical function, enabling real-time communication between control devices like PLCs and I/O devices such as frequency converters, sensors, and actuators. To support this, the network must prioritize or assign higher interrupt levels to such data. Configuration services allow users to set up and maintain automation equipment, often through PCs. These services need to run even while the control system is active, such as in batch processing for recipe management. Lastly, data acquisition enables users to collect operational data for HMI displays, analysis, and maintenance. A reliable network must efficiently support all three services to enhance the overall performance of the automation system.
The producer/consumer communication model is more effective than the source/target model in supporting control, configuration, and data collection. In the application layer, distributed objects and the producer/consumer model are used to meet the needs of automation systems. As shown in Figure 1, a typical industrial automation network includes multiple layers, each with different physical and data link layers. Therefore, a multi-layer architecture is necessary, ensuring consistency across networks for seamless data exchange.
Figure 1 shows a typical structure of an industrial automation network. The information layer uses Ethernet, widely supported by many controller vendors. The control layer, such as ControlNet, relies on deterministic networks and media redundancy. The device layer, like DeviceNet, requires less data transfer and durable cabling. ODVA and ControlNet International introduced EtherNet/IP, a CIP-based protocol that supports control, configuration, and data collection over Ethernet, making it suitable for both information and control layers.
II. Implementation of CIP Protocol on Ethernet EtherNet/IP is divided into several chapters and appendices, as shown in Figure 2. The three networks—EtherNet/IP, DeviceNet, and ControlNet—share a unified application layer, object library, and device description. In the OSI seven-layer model, they only use the first four layers. By leveraging these protocols, EtherNet/IP optimizes control, configuration, and data collection, making it practical, safe, and reliable in industrial settings.
III. Coexistence with Other Internet Protocols A major advantage of EtherNet/IP is that it allows users to leverage existing Ethernet knowledge and infrastructure, maximizing their return on investment. Many vendors offer Ethernet equipment, reducing costs and helping users build cost-effective control systems. However, if EtherNet/IP is limited to specific vendor hardware or requires a dedicated environment, its benefits diminish. Therefore, EtherNet/IP must coexist with existing Internet and intranet protocols, primarily using TCP/IP.
A. Ethernet Communication Protocol Ethernet defines the physical medium and access mode (CSMA/CD), using a simple frame format for LAN communication. It lacks advanced features for full LAN applications, so upper-layer protocols like TCP/IP are needed for data transmission and network management. Among these, TCP/IP has become dominant due to its global internet connectivity and enterprise intranet capabilities. As shown in Figure 3, TCP/IP operates above Ethernet, becoming the key protocol in industrial networks.
B. Origin and Characteristics of the TCP/IP Protocol TCP/IP is widely supported across computer platforms and is integrated into operating systems like Windows NT and Windows 2000. It enables integration of diverse devices into a LAN. TCP/IP follows a layered structure, corresponding to the OSI model. IP handles the network layer, while TCP and UDP manage the transport layer. The application layer includes protocols like HTTP, FTP, and SMTP, which define communication mechanisms. RFC documents, maintained by the IETF, detail these protocols and ensure interoperability across manufacturers.
C. Application Layer Protocols and Interoperability While TCP/IP ensures data transmission, it does not guarantee device interoperability. For this, application layer protocols must be standardized. Although general services like FTP and Telnet are well-defined, industrial automation faces challenges. Devices from different manufacturers may use varying application layer protocols, preventing seamless communication. EtherNet/IP solves this by coexisting with any existing protocol, running on top of TCP/UDP, and enabling interoperability across vendors.
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