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-e ectiveness 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 tra c control mechanisms. In this work, we present the design, implementation, and programming interface of a software-based tra c control protocol called RETHER , which turns o -the-shelf Ethernets into real-time networks without any hardware modi cations. 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.