WO2009000544A1

WO2009000544A1 - Communication system for transferring communication information within a railway train

Info

Publication number: WO2009000544A1
Application number: PCT/EP2008/005254
Authority: WO
Inventors: Luc De Coen; Gernot Hans
Original assignee: Bombardier Transportation Gmbh
Priority date: 2007-06-27
Filing date: 2008-06-27
Publication date: 2008-12-31
Also published as: GB0712526D0; GB2450520A

Abstract

The present invention refers to a communication system for transferring communication data within a railway train. The communication system comprises a data bus (ETB, ECN) adapted to transfer communication data according to the Internet Protocol via point-to-point connections. Devices (A1, A2) are connected to the data bus (ETB, ECN), wherein the devices (A1, A2) are adapted to receive and/or send safety-relevant data via the data bus (ETB, ECN). In particular, the train comprises at least a first device and a second device (A1, A2), wherein the first device and the second device (A1, A2) are adapted to perform a safety-relevant function of the train (like traction or braking the train), wherein the first device and the second device (A1, A2) are connected via the data bus (ETB, ECN) in order to trans- fer first data which are essential for performing the safety-relevant function and wherein the first device and the second device (A1, A2) are connected to each other, in addition to the data bus (ETB, ECN), by a separate data connection (TCL4, TCL1 ) in order to transfer second data which are essential for performing the safety-relevant function.

Description

Communication system for transferring communication information within a railway train

The present invention relates to a communication system for transferring communication information within a railway train. More particularly, the present invention relates to controlling devices of the train, like passenger doors, the traction system of the train and the braking system.

WO 2005/067142 mentions in the introductory part a train having a backbone network based on standard Ethernet or an adaptation of Ethernet which allows for high-speed applications on-board transit vehicles. According to WO 2005/067142, Ethernet is a type of networking technology for local area networks. Data is broken into packets and each packet is transmitted using the Carrier Sense Multiple Access / Collision Detect (CSMA/CD) algorithm until it arrives at the destination without colliding with any other packet.

Ethernet was originally designed as a multi-drop bus system with a transmission rate of 10 MBit/s. In order to increase the bandwidth, Ethernet technology, which is standardized in IEEE 802.3 (Institute of Electrical and Electronics Engineers, Inc.) was modified into a switched (point-to-point) technology. I.e. the packets are transferred from one point (or node) in the communication network to a single destination (the other point or node) in the network, allowing nowadays transmission rates ranging from 100 MBit/s (so called "Fast Ethernet") up to 10 GBit/s, and in near future, also higher. A node may be represented by a switch.

According to WO 2005/067142, packets may be sent simultaneously from different nodes so that a collision occurs. The document proposes using the HomePNA standard instead of the Ethernet standard in order to avoid collision of data packets. HomePNA uses only one two-conductor cable instead of two for Ethernet and HomePNA may share existing wires where Ethernet may not. Therefore, the network system has a pair of conductors forming at least a part of a two-conductor based network, and plural network communicative devices. Each network communicative devices has an application unit and a controller for communication of data between the application unit and the two-conductor based network. The controllers support data packets according to the Internet Protocol (IP). The controllers may be embedded within the application units or they may be distinct. For example, the application may be a multimedia broadcasting application for transferring media data (like video or audio data) via the train network. Although collision of packets may be reduced by certain network technologies or communication protocols, safety-relevant data are not transferred via high-speed IP-based data transfer systems in railway trains these days. In particular, safety-relevant data refer to the control of train systems which are essential for the immediate non-delayed operation of the train. Besides the problem of collision of packets, a data communication network must ensure that the data packets will arrive at the destination within a predefined time interval ("within real time"). Examples for safety-relevant train devices and systems are: the doors, which are used by passengers for entering and leaving the train, the traction (or propul- sion) system, which enables the train to accelerate and keep its velocity, and the braking system, which guarantees that the train can reduce its velocity and can stop.

Furthermore, diagnostic and measuring systems may also be safety-relevant. An example for such messages is a fire alarm signal. There are devices for generating, receiving and/or processing safety-relevant messages in the train. However, the predefined arrival time interval for signals within diagnostic and measuring systems may be longer than for doors, traction and brakes.

Safety-relevant data or information is understood to be data or information for the safe operation of the train. In particular, all devices and systems which are necessary for the basic functions of the train (traction, brake and doors to the outside) need safety-relevant data or information. For example, signals to these devices must reliably arrive in time. Otherwise, the train may fail to brake, may not escape from a dangerous position on the rail track or the doors to the outside may not be blocked in time before another train passes.

Another category of safety-relevant data or information has been mentioned: The diagnostic and measuring information. However, this type of data or information is not as safety- relevant as the other type. Diagnostic and measurement information therefore does not belong to safety-relevant data or information in the narrower range.

Although connections to safety of train operation may be imagined, multimedia data do not belong to safety-relevant data according to the present description. For example, the video information obtained by a surveillance camera may be used to identify damages or criminal actions within the train. However, the video information can be evaluated later and it is not absolutely essential that the video information is completely transferred. Therefore, the meaning of safety-relevant data in the narrower range is understood to be data or information which is used to operate the train, except operational functions which only serve to increase the comfort of the passengers or personnel.

It is an object of the present invention to provide a communication structure for a railway train which can be used to communicate data of safety-relevant train systems reliably and in real-time. The structure shall be simple and, preferably, shall allow transferring data of additional applications, such as multimedia applications (e.g. video surveillance, audio data for passenger mobile phones, video data for passenger entertainment), diagnostic applications, informing passengers.

A communication system for transferring communication data within a railway train is proposed together with a corresponding communication method. It is a basic idea of the present invention to use a data bus adapted to transfer communication data according to the Internet Protocol via point-to-point connections. Examples of such a data bus have been described above. The data bus is used to transfer at least a part of safety-relevant data within the train. Further means may be provided in order to guaranty that the safety- relevant data are transferred to the destination reliably and/or in time. In the following description, a specific structure of the data bus and/or the whole communication system of the train is given. The different aspects and embodiments can be combined in practise or can be realised alternatively.

According to one aspect of the invention, the data bus comprises a ring structure having at least two parallel lines which can be used alternatively or in addition to the other line (s) for transferring the communication data from one point in the data bus to a destination point in the data bus.

A point in the data bus can be realised by a terminal device or a switch, for example. Usually, data busses according to the Ethernet (IEEE 802.3-standard) contain several switches for distribution of data packets within the bus system.

The parallel lines of the ring structure are preferably connected at their opposite ends to each other. Optionally, further connections between the parallel lines are realised. For example, there is at least one switch for distributing data at each end of each of the paral- IeI lines. The ring structure has the advantage that there are redundant paths of travel. If one of the paths or lines is blocked, interrupted or busy, there is at least one other path or line.

Preferably, the parallel lines of the ring structure extend through all railway cars which form a functional unit that can be operated separately from other functional units. The functional unit may have a single railway car or plural cars which are coupled together. In the latter case, the coupling includes connecting of line sections within the single cars in order to achieve the parallel lines extending through all cars of the functional unit. A term which is used in practise for such a functional unit is "consist", which is understood to be a single railway car or a plurality of railway cars coupled together, wherein all railway cars of the consist share a common communication system or all share a common part of the train's communication system.

In addition to the ring structure or alternatively to the ring structure, there is preferably a backbone line of the data bus extending through all cars of the train. The backbone line may comprise several switches where connections to and from the backbone line are connected. This structure makes it possible to easily couple additional cars to the data bus by connecting an additional line section within the additional car to the backbone line of the train.

Advantagely, the backbone line is provided in addition to the at least one ring structure. Furthermore, it is preferred that the backbone line has at least two connections to each ring structure, for example a first connection at one end of the parallel lines of the ring structure and another connection at the opposite ends of the parallel lines of the ring structure. Therefore, a failure of one connection still allows to route data from the ring structure to the backbone line or vice versa.

Further parts of the whole communication system of the train can be connected to the backbone line and/or to the ring structure. For example, such a further part may be a Wire Train Bus (WTB), a Controller Area Network (CAN-Bus) and/or a Multifunction Vehicle

Bus (MVB). In addition or alternatively, a conventional train control line for connecting one device with a single other device in the train may be provided and at least one of these devices may be connected to the data bus and/or the other busses. This embodiment belongs to a second aspect of the present invention which is defined in the following.

According to the second aspect of the present invention, the train comprises at least a first device and a second device, wherein the first device and the second device are adapted to perform a safety-relevant function of the train, wherein the first device and the second device are connected via the data bus in order to transfer first data which are essential for performing the safety-relevant function and wherein the first device and the second device are connected to each other, in addition to the data bus, by a separate data connection in order to transfer second data which are essential for performing the safety-relevant function.

This solution combines the advantages of direct connections between devices (namely high reliability and immediate, non-delayed arrival of information) with the advantages or point-to-point data busses using the Internet Protocol. Advantages of IP-data busses are:

Using the internet protocol technology which is highly developed and allows transferring data not only within the data bus but also via other lines or other data busses which are connected to the data bus.

Using the same data bus for different types of information, such as multimedia data (audio and video), diagnostic data, measurement data, publicly available information and password-protected private information.

- There are existing bus-types which allow the transfer of high data volumes per time unit, such as data volumes of more than 1 GB/s.

- The IP-data bus may be connected to other communication systems by a wireless connection. For example, a so-called gateway may be connected to the data bus of the train.

As a result, the hardware and wire ring effort for conventional communication lines within the train can be reduced to an absolute minimum. The minimum is defined by the requirements of the operator. If the operator requires that certain types of information must reliably arrive at the destination within a time interval which cannot be guaranteed by the data bus, this type of information is transferred via the additional data connection which is separate from the IP-data bus.

According to one embodiment of the invention, the first data, which are transferred via the data bus, contain information about at least one of plural possible modes of performing the safety-relevant function. The second data, which are transferred via the separate data connection, contain a signal to initiate, to stop, to enable and/or to disable the perform- ance of the safety-relevant function. In this case, the second data can absolutely reliably be transferred to the destination device, whereas the less critical first data are transferred via the data bus. Possible modes of the safety-relevant function may be the level of the braking force of the braking system of the train, the level of the traction force of the trac- tion system of the train and the information if some specific doors of the train to the outside are blocked and/or released for opening. Other information for the doors, which can be transferred via the data bus, may be a signal to open or close a specific door. On the other hand, the signal to close all doors or to block or release all doors is preferably transferred via the additional data connection. In the case of the door system, but also in some other cases, the additional data connection may be a so-called ring line which connects the essential controlling device of the train with each door (or each device of same or similar type), wherein the doors or devices are connected in series. It is possible, that only one cable or wire is used for the connection from door to door (or device to device) and that the back path of the ring is realised by ground or mars, i.e. by electrically conductive parts of the cars and/or by the rails.

In case of a safety-relevant message which is to be transferred within the train, the first data may comprise the information where the measuring device or signalling device is located within the train (for example a device which detects a fire). The second data, which are transferred via the additional connection, may comprise the information that the relevant event happen (for example that the fire started).

Although the data transfer via the data bus may be less reliable than the data transfer via the separate communication line, the data bus still increases the reliability of the whole communication system. In the rare cases where the additional communication line is interrupted or fails to work, the information transferred via the data bus still allows to determine that a specific event has happened, for example fire. In another case, a control signal (for example in order to initiate or stop the performance of a function) may be transferred via the additional data connection and via the data bus. If the transfer via the additional data connection fails, the control signal can arrive via the data bus.

General speaking, the device or unit from which the data to be transferred originates may be a controller or control device (for example a computer) and the destination device may be a controlled device (such as a door controller, a traction device or a brake). The con- trolled device may be a controller itself. It is an advantage of the combination of the data bus with the separate data connection that the number of additional separate data connections can be reduced. In particular, the mounting effort for mounting the cables or wires within the cars and for connecting the cable or wire sections of neighbouring cars together is significant. On the other hand, since the data bus is required in present times for multimedia applications, it is only necessary to connect additional devices to the data bus and to configure the communication system accordingly.

Examples and preferred embodiments of the invention will be described in the following with reference to the attached figures.

Figure 1 shows a communication system extending through different railway cars of a railway train,

Figure 2 shows a detail of the communication system of Figure 1 for illustration of different paths which can be used for transfer of data packets, Figure 3 shows a grid structure of a data bus which may be used alternatively to the structure shown in Figure 1 and Figure 4 shows a further alternative of a data bus structure having a star configuration.

In the example shown in Figure 1 , a consist comprises three railway cars C1 , C2, C3. The consist may be coupled to further railway cars or consists or to a locomotive at one end of the consist or at both ends of the consist.

As shown in the lower part of Figure 1 , the consist comprises a part of the train's communication system. There is a ring-like structure ECN which is formed by two parallel lines 2, 3 extending through all three cars C1 , C2, C3, by one ring switch RS at each end of both parallel lines 2, 3 and by each one connection 4, 5 between the two ring switches RS at the same end of the parallel structure of the lines 2, 3. In addition, there is a further switch S connected to one of the lines 3. Three devices A4, A5, A6 are connected to the switch S so that they can communicate using the ring-like data bus ECN. Each of the terminal devices A4, A5, A6 may comprise a host having a destination address known to other de- vices in the communication system. More switches S may be connected to the structure ECN for connecting more terminal devices to the structure. Examples of the terminal devices A4, A5, A6 are controllers for controlling the operation of components of the heating and air conditioning system of the train, of doors (internal doors and/or doors to the outside of the train) and of multimedia devices like speakers and microphones, displays and CCTW cameras or screens. Two of the ring switches RS at the ends of line 2 are connected to a train switch TS. The train switches TS are connected to a train backbone bus ETB which extends through the whole train. The train backbone bus forms a data bus connection from the consist shown in Figure 1 to other parts of the train. These other parts of the train may also comprise a ring-like data bus structure or another bus structure which is connected to the train backbone bus ETB via a train switch TS or via plural train switches TS. One of these other train switches TS in other parts of the train is shown on the right hand side or Figure 1. The borderline between the consist and the other part of the train is marked by a double dashed line.

In the example shown, the train backbone bus ETB comprises two pairs of wires so that a full duplex data transfer is possible between the train switches TS. This increases reliability and bandwidth of the backbone. However, it is not necessary that all sections between in each case two train switches TS are realised by two pairs of wiring. In particular within the consist shown in Figure 1 , data from one train switch TS to another train switch TS may be routed as well through the structure ECN.

One of the ring switches at the end of line 2 is also connected to a gateway MCG for realising a wireless connection to other networks like the internet or private communication networks, such as the communication network of the operator of a fleet of trains.

One of the ring switches RS at the end of line 3 is connected to a control computer CC for controlling functions relating to the comfort of passengers or personnel, such as heating, air conditioning and multimedia applications. The computer CC may control applications like the controllers mentioned in connection with terminal devices A4, A5, A6 by transferring data via the structure ECN.

The structure ECN is preferably a communication network according to the Ethernet standard (IEE 802.3). However, the structure ECN may alternatively be a communication bus according to another standard, for example MVB, TCN or WTB. In any case, it is preferred that the Internet Protocol (IP), in particular the Transmission Control Protocol (TCP) is used to transfer the data via the structure ECN and via the train backbone bus ETB.

Both ring switches RS at the ends of line 3 are connected to in each case one computer CO which is adapted to control operational functions within the consist other than the functions controlled by computer CC. These operational functions may include the traction of the consist, the braking system of the consist, auxiliary devices for supporting the trac- tion system or the braking system of the train. Also, the applications mentioned in connection with the terminal devices A4, A5, A6 may alternatively be controlled by the computers CO.

Furthermore, the computers CO are connected to each other via an additional communication line or communication bus. In the example shown in Figure 1, this communication bus is a bus according to the train communication network (TCN) standard.

Several terminal devices A1 , A2, A3 may be connected to the bus TCN. As indicated in Figure 1 by the repeated pattern of terminal devices A1 , A2, A3, the same or similar kinds of terminal devices may be located in each of the cars C1 , C2, C3 of the consist. Examples of the terminal devices are controllers for the operational functions mentioned before, such as door controllers, controllers for traction and brake controllers.

Like the structure ECN, the communication line TCN between the computers CO is limited to the consist.

The structure ECN and the train backbone bus ETB may form the data bus for transferring data packets within the train according to the IP. The additional communication line TCN may be operated using different transfer protocols. Consequently, information which is transferred from the structure ECN to the line or bus TCN or vice versa must be transformed within the computer CO from one transfer format to the other transfer format.

Figure 1 also shows at the bottom part that at least some of the terminal devices A1 , A2, A3 are connected to additional communication lines TCL1 , TCL2, TCL3, TCL4. In the example shown, each terminal device A1 in the three cars C1 , C2, C3 is connected to a data bus TCL4 having different branches. On the other hand, the terminal devices A2 in the three cars C1 , C2, C3 are connected to an individual communication line TCL1 , TCL2, TCL3. These communication lines TCL1 to TCL3 may be conventional train control lines connecting one device (the terminal device A2) with one other device (not shown in Figure 1 ), which may be a computer in or near a driver compartment of the train driver.

The structure shown in Figure 1 allows transferring different kinds and/or the same kind of information to and from the terminal devices A1 , A2, A3 via different communication paths. Examples have been described before. One example is that the signal to release all doors in the train is transferred via the communication line TCL4 to terminal devices H1 (the door controllers), but to transfer the signal for opening an individual door is trans- ferred via the train backbone bus ETB, the structure ECN and the communication line TCN to the door controller, for example the door controller A1 in car C1.

Due to the structure of the data bus system ETB, ECN having redundant paths and con- nections between the bus ETB and the structure ECN and within the structure ECN, the data transfer is highly reliable. If necessary, for example when one path in the bus system is blocked or busy, the data packets can be routed via other paths. One of the different possibilities to transfer the information to the terminal devices is illustrated in Figure 2.

Figure 2 shows a central computer COM which may be the computer in the locomotive or driver cabin of the train. When the train driver or an automatic system of the train sends a signal to terminal device A1 or A2 via the bus system ETB, ECN, the corresponding data packets may be routed via the nodes shown in the top line of Figure 2, namely via two train switches TS of the bus ETB₁ three ring switches RS of the structure ECN and via the computer CO. Another alternative would be that the data packets are routed via three train switches TS, two ring switches RS and the computer CO in car C1. A further alternative would be that the packets are routed via two train switches TS, the ring switches RS in car C3 and the computer CO in car C3. In any case, the central computer COM transfers highly safety-critical signal like the command to initiate the braking of the train, via the direct communication line TCL1 or TCL4 to terminal device A2 or A1.

Figure 3 and Figure 4 show alternative structures of the communication system in simplified form. The IP based data bus indicated by reference symbol EN. The bus EN has grid form in the example of Figure 3 which means that different lines 13, 14 are interconnected by different connections 15, 16, 17. Switches within the bus EN are denoted by reference sign N. The vertical dashed lines are the borderlines of neighbouring train cars or consists. The bus EN serves to transfer data to terminal devices A within the cars and at least some of the terminal devices A are also connected to an additional communication line TCN (which may be a train communication network) extending through the whole train or at least extending from the controlling device which controls the terminal devices A to the terminal devices A. The structure of the example shown in Figure 4 is similar to the structure shown in Figure 3, but there is only one line of the bus EN extending through all cars and applications at least in car C1 are star-connected to one node of bus EN. Star- connected means that each of the terminal devices A has an individual connection to the node N. Furthermore, two of the terminal devices are in car C1 have additional connections to the separate communication line TCN. The data which are transferred via the data bus ETB, ECN (Fig. 1 ) or EN (Fig. 3 or 4) may comprise data for video surveillance, diagnosis of equipment on the train (wherein the diagnostic function may be based on Internet services), voice over IP services, enhanced passenger information, video on demand or wireless Internet access. It is an advantage of the present invention, that safety-relevant data (in particular control data) can be transferred via the data bus in addition to this kind of data.

In particular, special technologies can be used to prioritise the safety-relevant data. For example, Real-Time Ethernet provides a separate, deterministic data channel for control data, and an open channel for all the rest. Other technologies to prioritise the safety- relevant data maybe VLAN (Virtual LAN), QoS (Quality of Service) and VPNs (Virtual Private Networks). Furthermore, firewalls or frame filtering can be integrated into the bus system in order to ensure the integrity of control data transmission.

The structure of the IP based data bus according to the present invention is preferably hierarchical like the example shown in Figure 1. However, it may be flat (i.e. having no hierarchical structure like in the examples of figure 3 and figure 4).

Hierarchical structure means that there is a first part of the bus which extends through the whole train, or at least through all cars and parts of the train which should be connected to the data bus. In the example of Fig. 1 , the first part is formed by the Ethernet train backbone ETB. A second part or plural second parts (the Ethernet consist rings ECN of the example of Figure 1 ) are connected to the first part, but do not extend through the whole train. The second parts are adapted to connect devices within a restricted area of the train, for example within a single car or within a consist. Data can be transferred within each second part without being routed through the first part and there is no direct connection between the second parts in different consists.

It happens quite frequently that railway trains are re-arranged. Cars or consists may be separated or connected to each other to forming trains having different numbers of cars or consists. Consequently, care must be taken that the addresses of the devices (including switches) are unique. On the other hand, the effort for adapting the address scheme should be kept low. A preferred solution for this problem will be described in the following.

The basic idea is to keep the addresses of the second parts unchanged and to adapt the addresses of the first part of the data bus if necessary. Consequently, the second part can be called "static" and the first part can be called "dynamic". In the following, further details of an exemplary embodiment are described. Although the embodiment comprises the Ethernet Train Backbone as the first part and an Ethernet consist network ECN having ring-configuration as the second part, other embodiments of a hierarchical structure can have the same or similar features as described in the following.

There are some railway specific requirements which affect the addressing scheme and therefore should be considered in the design:

1. A consist forms a communication subnet of its own which shall remain in operation also during train composition changes when a train-wide communication is interrupted.

2. As it is typically the case for (international) passenger trains, trains are composed of vehicles from different manufacturers and different railway operators. It shall not be required to establish a central organization which assigns unique network ad- dresses (IP addresses) to the individual network devices in all the trains which are in the responsibility of that organization. Even if only vehicles of one manufacturer and one operator are coupled, which indeed is the most general case, the avoidance of a central administration for address assignments should be a clear goal.

3. A train wide IP addressing scheme should comply with the structure as defined in the leaflet UIC 556 (leaflet number 556 of the Union Internationale des Chemins de

Fer), e.g. the address should contain the vehicle sequence information.

4. Replacement of defective components as well as the installation of components during commissioning shall be facilitated as much as possible. Best would be to have a "plug-and-play" behaviour. One consequence of that could be to assign a defined IP Source Address to each component, related to its type and its installation place. A component, installed in different consists, could then have the same IP Source Address.

Defining an appropriate addressing scheme for the train IP network is a challenging task due to the dynamic nature of the Ethernet Train Bus. Dynamic are the number and sequence of consists which form a train, but also the switching between redundant functions if the active function breaks (example: redundant driver's display). The ultimate goal of the addressing scheme is to allow applications to address functions in and outside a train on a logical level, hiding all the details of mapping those logical addresses to the physical addresses. Logical addressing is in the IP world typically implemented by using ASCII strings like "driver_display.leading_car.train447.sncf\ which in this case identifies the (active) driver's display in the leading car of train447 in the fleet of SNCF. These "domain names" are then translated to TCP/UDP (Transmission Control Protocol /User Datagram Protocol) port numbers and IP addresses (by a DNS Name Server, DNS means Domain Name System), and then further translated to the physical Ethernet MAC (Media Access Control) address.

As mentioned before, the overall train network is hierarchical with one subnet (second part of the data bus) per consist, and a single train subnet spanning over the train. Optionally, there may be more than one subnet (second part of the data bus) in at least one of the consists.

Principally, an IP network on a train is nothing else than any other local stationary IP network. There are two possibilities how the IP-train network can be embedded in the operator's network (which not only includes one train, but several or many trains, i.e. the fleet). One possibility is to reserve a certain private address domain for a whole fleet, wherein the IP train network is a direct part of it. This concept is called "static" addressing. The problem with this is the administration overhead, because all IP devices in the fleet must get a unique IP address. This is practically impossible for large fleets or even international passenger trains. The second possibility is to define for each train a local address domain of its own (dynamic addressing). However, overlapping address ranges between different trains may occur. Furthermore, the problem must be solved how the operator's network and the train network can be connected address-wise.

Static addressing is quite obvious and needs not to be further discussed. With IPv6 (Internet Protocol version 6, a network layer protocol for packet-switched internetworks), static addressing will be used everywhere, but as long as IPv6 is not broadly available and supported by network components, dynamic addressing based on IPv4 (Internet Protocol version 4) seems to be the only alternative.

With dynamic addressing, the drawbacks of the static addressing (IPv4 only), namely the assignment of unique IP addresses to all devices in a complete fleet, can be avoided.

The basic idea is, to require unique address assignments only on consist level. As a consequence, different consists in a train may have overlapping address assignments, and it must be defined how these consists can communicate among each other without getting confused because addresses are not unique. The key to this is to define two levels of addressing, a train level and a consist level. On train level, all addresses in a train are unique, independent from the composition of a train which may change over time. How this works in principle will be explained next. First, the IP address domain needs to be defined: For dynamic IP addressing, each train shall form one private IP address domain, for example 192.168.0.0/16. This address is then further structured in the following way:

192.168.v.h

wherein v is the vehicle number and h is the host identifier (host ID). Alternatively, address range 10.0.0.0/8 may be used, for example. The host is part of the respective device which is connected to the data bus. Here, the vehicle number is equal to the consist number. If a consist has more than one vehicle or car, only one vehicle number is assigned to the whole consist. This means that the consist is the unit which forms the basis for structuring the address in this case, not the vehicle or car. However, further address structuring elements, such as a counter value which uniquely identifies each car or vehicle (or an- other sub-unit of a consist) may be used in addition.

The pair v.h then uniquely identifies one IP destination device within the train, where the V may change when the train composition is changed. As it is not practicable to assign such a dynamic address to a terminal device as IP source address (SA)₁ each terminal device in a consist shall be assigned a unique (which is unique on the level of the consist) IP Source Address, for example 192.168.0.h. Note, that the vehicle number is always set to 0 for terminal devices, indicating that the host or device is located in the own consist.

The vehicle number v changes dynamically with the composition of the train so it can fol- low the rules of UIC556 for vehicle numbering. For example, to address the brake controller (SA: 192.168.0.14) in vehicle 8, the destination IP address (DA) must be set to 192.168.8.14

Due to the private nature of the defined train address, domain frames are not routed out- side the train's private network. For the communication with the operator's network (including the fleet) it is therefore required to use proxies or Network Address Translation (NAT) techniques.

With this definition of the addressing scheme, the way how addresses are translated be- tween the Ethernet Consist Network and the Ethernet Train Backbone in the Train Switch is quite natural.

Claims

1. Communication system for transferring communication data within a railway train, wherein • the communication system comprises a data bus (ETB, ECN) adapted to transfer communication data according to the Internet Protocol via point-to- point connections, and

• devices (A1 , A2) are connected to the data bus (ETB, ECN), wherein the devices (A1 , A2) are adapted to receive and/or send safety-relevant data via the data bus (ETB, ECN).

2. The system of claim 1 , wherein the safety-relevant data are used to operate the train.

3. The system of claim 2, wherein the safety-relevant data comprise control data for controlling the braking system and/or the traction system of the train.

4. The system of claim 2 or 3, wherein the safety-relevant data comprise data for operating doors of the train, which are used by passengers for entering or leaving the train.

5. The system of one of claims 2 to 4, wherein the safety-relevant data comprise message data of messages about safety-relevant processes within the train and/or outside of the train.

6. The system of one of claims 1 to 5, wherein the data bus (ETB, ECN) comprises a ring structure (ECN) having at least two parallel lines (2, 3), which can be used alternatively or in addition to the other line(s) (2, 3) for transferring the communication data from one point (COM) in the data bus (ETB, ECN) to a destination point (CO) in the data bus (ETB, ECN).

7. The system of claim 6, wherein the data bus (ETB, ECN) comprises a backbone line (ETB) extending through all cars of the train, wherein the backbone line (ETB) is connected to the ring structure (ECN) via at least two different connections, each connection connecting one point (TS) of the backbone line (ETB) with one point (RS) of the ring structure (ECN).

8. The system of claim 6 or 7, wherein the parallel lines (2, 3) of the ring structure (ECN) extend through a consist, which is a single railway car or a plurality of railway cars (C1 , C2, C3) coupled together.

5 9. The system of claim 8, wherein the train comprises at least two consists, each consist containing at least one of the ring structures (ECN).

10. The system of one of claims 1 to 9, wherein the train comprises at least a first device (COM) and a second device (A1 , A2), wherein the first device (COM) and the o second device (A1 , A2) are adapted to perform a safety-relevant function of the train, wherein the first device (COM) and the second device (A1 , A2) are connected via the data bus (ETB, ECN) in order to transfer first data which are essential for performing the safety-relevant function and wherein the first device (COM) and the second device (A1 , A2) are connected to each other, in addition to the5 data bus (ETB, ECN), by a separate data connection (TCL4, TCL1 ) in order to transfer second data which are essential for performing the safety-relevant function.

11. The system of claim 10, wherein the first data contain information about at least 0 one of plural possible modes of performing the safety-relevant function and wherein the second data contain a signal to initiate and/or to stop the performance of the safety-relevant function.

12. The system of claim 10, wherein the first data contain information about at least 5 one of plural possible modes of performing the safety-relevant function and wherein the second data contain a signal to enable and/or to disable the performance of the safety-relevant function.

13. A method of transferring communication data within a railway train, wherein 0 • the communication data is transferred via point-to-point connections of a data bus (ETB, ECN) according to the Internet Protocol, and • the data, which are transferred via the data bus (ETB, ECN), comprise safety-relevant data.

14. The method of claim 13, wherein the safety-relevant data are used to operate the train.

15. The method of claim 14, wherein the safety-relevant data comprise control data for controlling the braking system and/or the traction system of the train.

16. The method of claim 14 or 15, wherein the safety-relevant data comprise data for operating doors of the train, which are used by passengers for entering or leaving the train.

17. The method of one of claims 14 to 16, wherein the safety-relevant data comprise message data of messages about safety-relevant processes within the train and/or outside of the train.

18. The method of one of claims 13 to 17, wherein at least a part of the communication data are transferred via at least one ring structure (ECN) of the data bus (ETB, ECN), wherein the ring structure (ECN) comprises at least two parallel lines (2, 3) which are used alternatively or in addition to the other line(s) for transferring the communication data from one point in the data bus (ETB, ECN) to a destination point in the data bus (ETB, ECN).

19. The method of claim 18, wherein at least a part of the communication data is transferred via a backbone line (ETB) of the data bus (ETB, ECN) extending through all cars of the train, wherein the part of the communication data is transferred via at least one of at least two different connections, each connection connecting one point (TS) of the backbone line (ETB) with one point (RS) of the ring structure (ECN).

20. The method of claim 18 or 19, wherein at least a part of the communication data is transferred from a first consist to a second consist, wherein a single consist is a single railway car or a plurality of railway cars (C1 , C2, C3) coupled together and wherein each consists comprises the parallel lines (2, 3) of at least one of the ring structures (ECN).

21. The method of one of claims 13 to 20, wherein the communication data are transferred from a first device (COM) of the train to a second device (A1 , A2) of the train, wherein the communication data comprise safety-relevant data to perform a safety-relevant function of the train, wherein a first part of the safety-relevant data is transferred via the data bus (ETB, ECN) from the first device (COM) to the second device (A1 , A2) or vice versa and wherein a second part of the safety-relevant data is transferred via a separate data connection (TCL1 , TCL4) from the first device (COM) to the second device (A1 , A2) or vice versa without using the data bus.

22. The system of claim 21 , wherein the first data contain information about at least one of plural possible modes of performing the safety-relevant function and wherein the second data contain a signal to initiate and/or to stop the performance of the safety-relevant function.

23. The system of claim 22, wherein the first data contain information about at least one of plural possible modes of performing the safety-relevant function and wherein the second data contain a signal to enable and/or to disable the performance of the safety-relevant function.