RETHER: A Software-Only Real-Time Ethernet for PLC Networks

The networking technologies used in industrial automation are required to support real-time performance guarantees to ensure that sensor/command data reach target nodes within a delay bound. With the continuing popularity and thus the accompanied price drop of the Ethernet technology, replacing the typically closed and proprietary automation networks with Ethernet is emerging as a very attractive solution, because of the cost-effectiveness and its compatibility with the trend of moving industrial control systems to PC-based hardware. Due to its contention-based media access control protocol, Ethernet theoretically can not bound the network access delay without additional traffic control mechanisms. In this work, we present the design, implementation, and programming interface of a software-based traffic control protocol called RETHER , which turns off-the-shelf Ethernets into real-time networks without any hardware modifications. RETHER works both in a single-segment as well as a multi-segment environment. This paper reports the performance measurements and implementation experiences with the RETHER prototype, which has been fully operational for over 12 months.