Ein Framework für echtzeitfähige Ethernet-Netzwerke in der Automatisierungstechnik mit variabler Kompatibilität zu Standard-Ethernet

Within the scope of automation technology, a trend to substitute established fieldbuses with realtime Ethernet networks or to integrate Ethernet frames into a fieldbus infrastructure can be observed since several years. The aim is to use a single network from the office area to the field devices like sensors, actuators or user-panels. This trend is characterized as vertical integration. A central issue is that widespread Standard-Ethernet networks do not satisfy the demands of industrial realtime in automation technology. However, the Ethernet standard ought to be observed in the field area as well. Otherwise, separate field bus infrastructures would arise again. The main objective of this work is the development of a formal profounded framework, which allows to vary between compability to the widespread
Ethernet standard on the one hand, and the compliance with concrete realtime demands of an automated plant on the other hand.
First of all, an overview and classification of existing realtime Ethernet solutions is given. These solutions mostly build subnets consisting exclusively of realtime devices. Though it is possible to transfer data in an asynchronous manner, a connected personal computer without knowledge about the realtime protocol would impact the realtime capabilities of the network. Standard Ethernet devices can only be connected via gateways. However, in this case a common fieldbus with Ethernet gateway can be used in the same manner. Furthermore, many existing solutions are based on a master/slave communication model. They do not consequently follow the trend towards decentral periphery, which allows concurrent communication in the network.
Within the scope of this work, the developed framework allows a new perspective on realtime networks for automation technology based on Ethernet. In addition to this, a new approach is depicted, which is based on a TDMA access method without enforcing strict subnets. Devices like laptops or personal computers can be added to the network and removed from the network seamlessly. They can transmit and receive asynchronous data without influencing the realtime capabilities of the network. In order to realise the TDMA access method, offline schedules are calculated with regard to the well known realtime communication requirements. Furthermore, the location for implementing the schedules in the network is discussed. In this context, a central scheduler is considered as well as decentral schedules inside the switches. Active transmitting devices are included as well as passive devices. Finally, the design of a new switching hardware is outlined. This switch will be able to transmit Ethernet frames with high realtime requirements deterministically and even faster than cut-through switches.