intermittent and continuous ATP 101119 - irse.nl

LZB data flowThe data available from the interlocking system (signal aspects, point settings,positions of level crossing barriers, etc.) are transmitted to the control centre. In theopposite direction, approach indications for level crossings are transmitted. A higherlevel dispatcher system (i.e. a district control centre) can supply dispatching andscheduling data and receive operating information such as speed and position oftrains from the LZB command and control centres.In addition data is exchanged with neighbouring command and control centres totransfer train information between two control centres in both directions. The dataflow to the train-borne units as specified by the ORE is vital, i.e. the command andcontrol centre transmits messages to the trains with commands determined by thecurrent condition of the total system. An operator terminal in the control centre allowsentry of data for track sections with temporary speed restrictions and output ofoperating or fault messages.Computer SystemA major feature of the LZB system is the use of off-the-shelf process computersfor calculating train commands in the command and control centres. The followingconsiderations suggest the use of commercially available computers:• powerful performance• flexibility in adapting programs to each system• high reliability by the use of highly integrated components• favourable price-to-performance ratioFail-safe commands are always computed by two different computers withdifferent program versions. The two results are compared by external or internalcomparators. For reasons of availability, a three-computer system is used in thiscase. If one processor of the three-processor system fails, fail-safe operation fromthe signalling point of view can be maintained with two computers. The real-timerequirements for the LZB computer system are very stringent. This is the reason forthe use of a three-computer system rather than a cold standby configuration. In caseof an interrupted data transmission, all trains would automatically be stopped. If oneof the active computers fails, the configuration is automatically changed without26