The issue of connectivity of the different vehicles constituting a train becomes important when managing the data captured by various onboard devices. A Train Data Bus or Train Communication Network (TCN) is needed to evacuate the data to a central gateway device on the train from where it can move to a central computing facility. The central computing facility can be on-board, or in a remote location, that can be accessed online through a wireless network, or asynchronously by downloading the data periodically onto a portable device and then loading it onto the central computing facility.
There are several alternatives for a TCN. Buses developed for use in automobiles have been used in the past, e.g., those based on Canbus, FlexRay etc. However, the accepted standard is the IEC 61375 set (adopted as IEEE 1473 Type T), first developed in 1999, and then updated between 2012 and 2021 (third edition). This comprises individual Consist Networks connected to a Train Backbone to form a Train Communication Network (TCN). It allows flexibility such that Consist Of Networks can be restricted to one physical vehicle or can span consists of several physical vehicles. These Consist of Networks can be based on the MVB (Multifunction Vehicle Bus), CANOpen, or switched technology. The Train Backbone can be based on Bus (Wired Train Bus – WTB) or Switched technology. The updated standard provides for on-board- to-ground communication through a router-based or application-layer Gateway to enable data transfer from running trains to wayside facilities.
A Train Topology Discovery Protocol (TTDP) defined by the IEC standard is used to achieve Train Inauguration procedures, i.e., the connection of additional vehicles to a train consists. The standard also defines the application profile for functions belonging to the Train Control and Monitoring System (TCMS) which is accessed by the operator (e.g., train driver, train staff). In addition, Onboard Multimedia and Telematic Services (OMTS) are also defined. Figure 10 – Application and Communication profiles in TCN The following list illustrates the wide range of applications that are needed on board running trains. The services mentioned below can be provided through devices and systems connected to the TCN.
a) Operational applications:
• Driver Assistance Application.
• Energy Meter Application.
b) Maintenance applications:
• Configuration data application.
• Monitoring train status (e.g., telemetry).
• Diagnostic data application.
• Event Recorder Application.
c) Multimedia application
• Passenger information application.
• Passenger entertainment application.
• Electronic ticketing application.
• CCTV and video surveillance.
The IEC 61375 standard is normally used only for passenger trains, whether locomotive-hauled or trainsets, because of the need for continuous power to the devices since Ethernet- based communication protocols are usually used. Freight trains are composed of freight wagons that typically do not undergo the intensive maintenance needed to provide power generators or external power supplies. Devices on these trains would typically have to make do with battery power, which entails using low-power communication protocols. The use of the TCN in such trains using low-power networks needs further exploration to arrive at practical and workable solutions.
Views expressed by Sharat Sahai Mathur, GGM/CCCO, Centre for Railway Information Systems (CRIS)
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