Comparative Analysis of Real-Time Industrial Ethernet Protocols : ModbusTCP Protocol Implementation

Abstract: Industrial Ethernet Communication protocols for Real-Time communication is the focus of research in a variety of different industrial Applications. The subject of thesis study is a comprehensive analysis of Industrial Ethernet protocols used in safety-critical real-time environment, comparing these based on performance, safety, diagnostics and error detection features, topology preference, cost incurred and openness of the protocol. The protocols chosen for this comparisons are ModbusTCP, EtherNet/IP, Ethernet Powerlink, Profinet IO, EtherCAT®, Sercos III, and CC-LINK IE, because they are most relevant for real-time applications and they have a widespread global presence in a lot of industrial applications. The industry in focus here is the spacecraft industry, which is a perfect example of a real-time safety-critical environment, where the protocols need to perform under harsh conditions, such as vibrations, exposure to radiation , extreme temperatures and low atmospheric pressure, and have strict timing requirements. The communication protocols for this environment are held to very high standards of performance and communication accuracy. The challenge here is to implement a protocol that can provide deterministic, real-time communication in such extreme conditions. The protocol in focus here is the ModbusTCP protocol , that is implemented on the ESBO-DS Stratospheric Balloon project to establish a communication link with the pointing system on board. ModbusTCP is chosen for this application because it is reliable, has a large support base, it is easy to implement, transparent and extremely interoperable. All these benefits along with providing real-time communication on a space-based application gives us a good reason to continuing the use of ModbusTCP here. The conclusion of the comparison of the selected real-time communication Industrial Ethernet protocols is that there is no “best ” protocol, and the choice of protocol depends on the application in focus. EtherCAT, SERCOS III and PROFINET IRT are all powerful hard real-time protocols, but require dedicated and expensive hardware for implementation. CC-Link IE is also a popular hard real-time protocol that uses special hardware and is well-established in the East Asian countries. Ethernet/IP and ModbusTCP control a large market share in the Industrial Communication domain in addition to providing good performance easily available tools. Ethernet Powerlink is open and provides both implementation and specification royalty free on its organisations website.