Train Communication Network

The Train Communication Network (TCN) is a hierarchical combination of two fieldbus systems for digital operation of trains. It consists of the Multifunction Vehicle Bus (MVB) inside each coach and the Wire Train Bus (WTB) to connect the MVB parts with the train control system. The TCN components have been standardized in IEC 61375.

Usage

The TCN is used in most of the modern train control systems usually connecting the vehicle parts with a 18-pin UIC 558 connector cable.

• Deutsche Bahn: ICE T, ICE-TD and ICE 3
• Swiss Federal Railways: IC2000 and EW IV
• Austrian Federal Railways: All Railjet and Talent trains

Wire Train Bus

The Wire Train Bus interconnect can be performed by an electric twisted pair cable or by an optical glass fiber. The standard connection is done with the UIC connector using a Shielded Twisted Pair cable. The physical level is using digital RS-485 transmission at 1 Mbit/s data rate. The encoding uses a Manchester II code and a HDLC frame protocol. There is a maximum of 32 nodes on a maximum length of 860 meters (without repeaters). With a maximum of 1024-bit payload per telegram, the system allows response times of typically 100 µs.^[1]

The Wire Train Bus shares some similarities with the earlier WorldFIP field bus (EN 50170 part 4) - its "voltage mode" did use 1 Mbit/s and a maximum of 32 stations on the bus with a maximum length of 750 meters. The WorldFIP was based on the earlier work on the FIP field bus (originally "Flux d'Information vers le Processus", relabeled as Factory Instrumentation Protocol and later Flux Information Protocol) that was developed in the French NFC 46602 standard series.^[2] (The FIP standard effort is the French analogue of the German Profibus standard effort that ran both in the late 1980s / early 1990s where eventually the Profibus components did prevail the market down the road). The WorldFIP connectors found usage in train equipment in France and North America (by Bombardier) until a joined effort on a common UIC train bus was started (with Siemens and other industry partners) that led to the WTB/MVB standard in late 1999.

Multifunction Vehicle Bus

The Multifunction Vehicle Bus interconnect can be performed by an electric Twisted Pair cable or by an optical glas fiber. Unlike the WTB there is no requirement on a single international connector standard for the vehicle bus inside a coach, locomotive or train set - instead there are three predefined connector classes for OGF, EMD and ESD media. Using optical glas fibres (OGF) a line distance of 2000 meter is possible, using shielded twisted pair with RS 485 (EMD, electrical medium distance) the allowable length reaches 200 meter and with a simple backplane wiring (ESD, electrical short distance without galvanic isolation) the cable may be up to 20 meter in length. The plugs and sockets are the same as used by Profibus (with two 9-pin Sub-D sockets per electrical device).^[3]

The media sources are usually connected by repeaters (signal generators) being joined on a central star coupler - the repeator is also responsible for the transition from one medium to another. The number of addressable devices depends on the configuration of the vehicle bus - there may be up to 4095 simple sensors/actuators (Class I) and up to 255 programmable stations (Class 2, with configuration slots). The physical level is using transmissions at a 1.5 Mbit/s data rate using Manchester II encoding. The maximum distance is determined on the restriction of a maximum allowed reply delay of 42.7 µs (where for longer distances a second mode is used that allows up to 83.4 with reduced throughput) while most system parts communicate with a response time of a typical 10µs.^[3]

Alternate Vehicle Buses

The MVB frames are not compatible with IEC 61158-2 fieldbus frames as it omits most of the preamble synchronization and mute spacing times.^[3] However most the modern development and test equipment can equally communicate WTB/MVB frames as well as Profibus frames on the line as the telegram structure is derived from Profibus.

The MVB standard was introduced to replace the multitude of field buses in the train equipment. This was noted to be not the case for several reasons. While the CANopen and Profinet are controlled by international manufacturer associations targeting wide compatibility this is not the case for MVB such that even for the two main manufacturers some incompatibilities have been noticed. Unlike other standards the MVB standard is missing usage profiles for specific applications. And reality has shown that MVB modules are more expensive as much as ten times the price for CANopen components. This has led to the observation that - despite the advantages of the MVB field bus - many train vehicle buses are still built from CANopen and Profibus components. Additionally more and more components are added to rail vehicles that need far more bandwidth than any of the field buses can provide to the effect that Ethernet IP is found in some modern train sets (according to the EN 501555 profile). Still all the alternate vehicle buses are connected to the Wire Train Bus.^[4]

External Links

1. ^ Prof. Dr. Hubert Kirrmann (1999-01-20). "Train Communication Network IEC 61375 - 4 Wire Train Bus" (powerpoint). Ecole Polytechnique Fédérale de Lausanne (EPFL). http://lamspeople.epfl.ch/kirrmann/Pubs/TCN/IEC61375-4-WTB.ppt. 
2. ^ WorldFIP
3. ^ ^{a b c} Prof. Dr. Hubert Kirrmann (1999-01-20). "Train Communication Network IEC 61375 - 3 Multifunction Vehicle Bus" (powerpoint). Ecole Polytechnique Fédérale de Lausanne (EPFL). http://lamspeople.epfl.ch/kirrmann/Pubs/TCN/IEC61375-3-MVB.ppt. 
4. ^ "Informations- und Steuerungstechnik auf Schienenfahrzeugen - Bussysteme im Zug" (in de). elektronik industrie 8/9 2008. InnoTrans Special: Bahnelektronik. 2008-09-14. http://www.all-electronics.de/media/file/4509. 

• Hubert Kirrmann (ABB Corporate Research); Pierre A. Zuber (DaimlerChrysler Rail Systems). "The IEC/IEEE Train Communication Network" (PDF). IEEE Micro March-April 2001: 81–92. 0272-1732/01. http://www.dca.ufrn.br/~affonso/DCA_STR/trabalhos/rt-diversos/The%20IEC-IEEE%20train%20communication%20network.pdf. 
• "The IEC / IEEE / UIC Train Communication Network for time-critical and safe on-board communication" (powerpoint). Bombardier Transportation. 2002-06-10. http://www.tsd.org/papers/apta2002zuber.pps.