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Abstract:
Data acquisition in shot-based fusion experiments is characterized by a huge amount of data collected within a short time. The Stellarator experiment Wendelstein 7-X will produce a considerable higher amount of data in a continuous and steady-state operation within half an hour.
For Wendelstein 7-X it is not sufficient to wait until all data has been acquired and stored in the database before being able to view and analyze data. A distributed data monitoring system has been developed for visualization of trends. This implies a completely new demand on continuous robust data transport via the network.
It is planned to use the LAN with commercial available standard hardware components for periodic as well as asynchronous communication between software modules. Fields of application include the data monitoring system, acquisition of PLC data, signaling between modules and continuous data traffic for distributed online analysis.
Therefore a general and easy-to-use network channel concept has been introduced. In contrast to existing TCP/IP based data pull techniques the network is treated as universal bus system like PCI or field bus systems. For data monitoring the underlying protocol is OSI layer 3 IP Multicast/UDP in a data push model with modules sending periodically and modules listening. No additional protocol overhead is added because the data structure is well-known to all modules. Plug in of other bus-like architectures is provided and has been proven for the shared memory hardware in use at the Asdex Upgrade Experiment.
The paper gives an insight into the network channel concept and the implementation covering the system-wide available data description, half sync/half async communication pattern, data serialization, identification and matching of data as well as possible security aspects.
In a special Multicast section the results of performance measurements are presented. Suitability and limitations are discussed and an appropriate answer to the question “When is IP Multicast/UDP reliable?” is given.
