Time-triggered Exchange Of Train Route Data Between Train Control Systems
Free (open access)
The increased heterogeneity and decentralisation of train control systems, often requiring the collaboration of several suppliers, calls for a simplification of the involved interfaces. Time-triggered protocols form a favourable alternative to the event-triggered protocols, which are still used in most vital computer-based applications involving data exchange. The advantages of time-triggered protocols include an increased robustness against transmission failures and a simplification of the underlying definitions. To take full advantage of time-triggered protocols, the used telegrams should be of fixed length whenever possible. This poses a problem in transmitting state information of ambiguous train routes, i.e., if there exist several such routes between a given pair of start and end point. To overcomes this problem, an algorithm to derive a unique route index is introduced. The proposed approach relies exclusively on geographical track layout data, without the exchange of explicit route tables between collaborating suppliers. As a means to represent track topology data and to introduce the route indexing algorithm, Double Vertex Graphs are used, which -in contrast to ordinary graphs - allow for a correct representation of the topological properties of railway tracks. The indexing scheme proposed here has been successfully applied in the pilot project of an ERTMS Level 2 system currently being commissioned by Swiss Federal Railways.