A new fault tolerant architecture for time sensitive automation networks

Networked control systems have been widely used in Industrial Automation since the latter part of the 20st century. Such networks have evolved from small systems with proprietary and slow Fieldbus technology to a much larger scope. Today, Ethernet-based automation systems encompass whole factories and carry large amounts of data traffic with differing latency requirements. Proprietary real-time Ethernet technologies such as Profinet IRT (Isochronous Real-Time) have demonstrated the feasibility of real-time Ethernet for even the most demanding applications such as functional safety and motion control. The drawback of these vendor-specific solutions is their dependence on proprietary ASICs (Application-Specific Integrated Circuit) and their very limited compatibility to standard Ethernet and Bridging as defined by IEEE (Institute of Electrical and Electronics Engineers) 802.3 and IEEE 802.1. Up to the present day, this has limited the widespread success of Ethernet as a real-time network solution. With the emerging AVB (Audio- and Video Bridging) technology, IEEE 802.1 has defined the first vendor-neutral real-time Ethernet, enabling the possibility of a standardised solution for Industrial Automation. However, the home automation scope in which AVB was developed leaves large feature gaps that prevent its adoption in mission-critical systems, for example the lack in support for faulttolerance technologies that are specific to Industrial Automation. These networks require built-in redundancy to prevent critical failures. While industrial-grade redundancy technologies are designed to support mission-critical automation with standard Ethernet, their combined usage with AVB mechanisms fails to meet many application requirements. This research work, carried out for the Advanced Development department of Hirschmann Automation & Control GmbH, investigates methods to enhance IEEE 802.1 AVB so it can be better used in networks that have firm fault-tolerance requirements. A requirement of particular interest is to enhance AVB so it can interoperate with any arbitrary and application-specific fault tolerance technology, so as to maximise its reach into new application domains. This work proposes an enhancement to the AVB Stream Reservation Protocol (SRP) to enable it to register communication streams over multiple network paths simultaneously. To verify the feasibility of the proposal, the protocol enhancement is implemented and verified by simulation within a detailed model of an Industrial Ethernet network. This simulation contains Ethernet switch and protocol models with behaviours and parameters that are based on existing products and specifications. This helps to ensure that the simulation results carry significance for real-world behaviour. This research also investigates the specific protocol requirements that are needed for the feasible use of the proposed solutions in future real-time network design, such as optimal methods to influence stream paths in relation to end-to-end latency and fault-tolerance.