Abstract:
An intra-train network management system is provided for a train having up to three or more train units. Each train unit consists of two terminal cars and zero or more intermediate cars between the terminal cars. A communications interface unit in each terminal car establishes at least two separate networks within its associated train unit. Each network connects to distinct nodes within the train unit, and the separate networks of coupled train units are crossed over. A gateway associated with each terminal car links the respective networks of separate train units coupled into a train. The network management determines the network topology by sending global device discovery messages throughout the network, and local discovery messages within each train unit that cannot penetrate the gateway(s) associated with that train unit. The local discovery messages resolve the ambiguity created by the global messages.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 USC 119(e) of U.S. provisional application No. 61/672,624 filed Jul. 17, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to the field of train management, and in particular an intratrain network management system for example for multi-unit trains operated using a Communication-Based Train Controller (CBTC). 
       BACKGROUND OF THE INVENTION 
       [0003]    Trains within modern transit systems are often controlled using CBTC technology, wherein the trains communicate with each other on a peer-to-peer basis over a broadband wireless network. One such exemplary system is known as Seltrac™ by Thales. 
         [0004]    Each train is made up of one or more train units, or vehicles, each of which train unit typically comprises two or more cars. Each unit has an OBCU (On-Board Control Unit) that communicates with other trains and controls the operation of the unit. Each car within each train unit contains at least one CIU (Communications Interface Unit) that establishes two separate networks between the nodes within the units for redundancy purposes. The separate networks are referred to as the left side and right side networks (known as the neuron ID). These networks are configured such that specific nodes in one car are linked to specific nodes in the other car. For example, in  FIG. 1 , the left side network links nodes 2 and 4 respectively in cars A1 and A2, whereas the right side network links nodes 1 and 3 respectively in cars A1 and A2. The arrangement in train unit 2 is similar. Nodes 6 and 8 are linked by the left side network and nodes 5 and 7 are linked by the right side network. 
         [0005]    While the cars within a unit operate at all times as a unit and are not separated during normal operation of the system, the units can be coupled together as desired to form longer trains under operator control. For example, in  FIG. 1 , two train units, each consisting of two cars, are joined together to form a two-vehicle (four-car) train. The number of cars in each train unit is not important. There could be any number of intermediate cars between the end or terminal cars shown. Each CIU is connected to a gateway for external communications. 
         [0006]    When the units are linked together, the networks in the individual units are linked together to form intratrain networks. The network sides in each unit are crossed over to ensure that the same network nodes in the train are connected to each other regardless of vehicle orientation. This arrangement works for trains consisting of only two train units. For example, in  FIG. 1 , the following four nodes are always connected: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 A1, right side node in vehicle 1 
                 (node 1) 
               
               
                   
                 A2, right side node in vehicle 1 
                 (node 3) 
               
               
                   
                 A1, left side node in vehicle 2 
                 (node 6) 
               
               
                   
                 A2, left side node in vehicle 2 
                 (node 8) 
               
               
                   
                   
               
             
          
         
       
     
         [0007]    In this system, each CIU can discover the network topology by broadcasting a global device discovery message. This is sent to all devices on the network, which respond accordingly and allow the CIU to build routing tables that allows it to reach any device with which it needs to communicate. 
         [0008]    However, this system does not work when three or more train units are coupled in tandem because certain corresponding network devices in different train units are coupled to the same network side resulting in an ambiguity as will be explained in more detail. Trains consisting of three or more units have been protected by manual procedures because no on-board automatic train protection (ATP) was provided by the CBTC system. Lack of on-board ATP increases the likelihood of a hazardous event (e.g. collision). 
       SUMMARY OF THE INVENTION 
       [0009]    According to the present invention there is provided an intratrain network management system for a train comprising up to three or more train units coupled together to form a train, each train unit comprising two terminal cars and zero or more intermediate cars between the terminal cars, the intratrain communication system, comprising a communications interface unit in each terminal car configured to establish at least two separate networks within its associated train unit, wherein each network connects to distinct nodes within the train unit, and wherein the separate networks of coupled train units are crossed over; and a gateway associated with each terminal car for linking the respective networks of separate train units coupled into a train; and wherein the network management system is configured to determine network topology within the train by sending: 
         [0010]    a) global device discovery messages throughout the network, and 
         [0011]    b) local discovery messages within each train unit that cannot penetrate the gateway(s) associated with that train unit. 
         [0012]    The local discovery messages may be sent out and managed by the communications interface units. 
         [0013]    The local discovery messages may be similar to the global discovery messages with the subnet mask set to a value that does not allow them to penetrate the gateway. These message resolve the ambiguity present in the prior art systems when more than two train units were coupled together. The discovery messages are preferably in the form of pings. 
         [0014]    By taking advantage of behaviours of the on-board network gateway devices that route network messages between vehicles, the network management software can construct a complete set of routing tables for a train consisting up to three train units. With a complete routing table defined, the OBCUs can determine the size of the train, and their location within it. Knowledge of the train size and their location allows the OBCUs to provide full on-board automatic train protection. 
         [0015]    In another aspect the invention provides a method of managing a network management in a train comprising up to three or more train units coupled together to form a train, each train unit comprising two terminal cars and zero or more intermediate cars between the terminal cars, comprising establishing at least two separate networks within its associated train unit, wherein each network connects to distinct nodes within the train unit, and wherein the separate networks of coupled train units are crossed over; and determining network topology within the train by sending: 
         [0016]    a) global device discovery messages throughout the network, and 
         [0017]    b) local discovery messages within each train unit that cannot penetrate the gateway(s) associated with that train unit. 
         [0018]    In a still further aspect the invention provides a communications interface unit for an intratrain network management system for a train comprising up to three train units coupled together to form a train, each train unit comprising two terminal cars and zero or more intermediate cars between the terminal cars, wherein the communications interface unit is configured to establish at least two separate networks within its associated train unit, wherein each network connects to distinct nodes within the train unit, and wherein the separate networks of coupled train units are crossed over; and wherein the communications interface unit is configured to determine network topology within the train by sending: 
         [0019]    a) global device discovery messages throughout the network, and 
         [0020]    b) local discovery messages within each train unit that cannot penetrate the gateway(s) associated with that train unit. 
     
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:— 
           [0022]      FIG. 1  is a diagram of a prior art intratrain communication system; and 
           [0023]      FIG. 2  is a diagram of an intratrain communication system in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring now to  FIG. 2 , three or more train units  10 , also referred to as vehicles, are coupled together to form a train. Each train unit or vehicle contains an OBCU  12  controlling overall operation of the train unit. In addition, each car contains a CIU  14  for managing the intratrain network. The CIU may suitably be a Thales CIU forming part of the Seltrac™ system. The train units form an integral unit during normal operation and are not separated under operator control. By contrast the separate train units can be coupled and uncoupled at will by the operator. This poses challenges since the network must reconfigure itself each time the train configuration is changed. 
         [0025]    With the exception of the novel aspect to be described the network management system generally operates in a conventional manner using a configuration based on LonWorks™ network technology developed by Echelon Corporation. A suitable CBTC system is the Seltrac™ system referred to above. 
         [0026]    The network topology is an important part of the architecture because it permits the OBCU  12  to identify which CIU  14  nodes are part of the same train unit via the nodes attributes, namely A1 or A2 car, left side or right side network. 
         [0027]    The problem of identifying a CIU to a train unit arises because of multiple limitations in the architecture that must be circumvented. The train unit Identification (ID) number, which is assigned to a train unit, cannot be transferred to all CIUs because in a CBTC system the train unit includes a Monitoring Diagnostic System (MD) connected to the CIUs in the A2 car CIUs and not to the A1. Using the CBTC network to transfer the information is not a valid option. The A1 car needs a train unit ID to find out in which train unit it is and to initialize the CBTC network. The A2 car needs an initialized CBTC network to send the ID of the train unit to the A1 car. 
         [0028]    The physical network topology of a multi-car train consist changes depending on how the cars are connected. While a changing topology is a problem in itself, some topologies, such as illustrated in  FIG. 1 , do not permit identification because of the symmetry in the attributes. 
         [0029]    A viable physical network connectivity solution requires that two rules be fulfilled. First, the network wiring should have a fixed network topology independent of the physical train interconnection. The possible physical train interconnections are: A1/A2 connected, A1/A1 connected, or A2/A2 connected. Second, the network wiring should have a configuration that permits node differentiation. 
         [0030]    One solution in accordance with an embodiment is shown in  FIG. 2 . In this solution there is no crossing of the left/right networks between A1 and A2 cars, whereas there is crossing of the left/right networks between the train units. 
         [0031]    In this case, the physical configuration should follow the rules: 
         [0032]    a) Two A1 CIU units, on separate train units, will always be connected to two opposite networks: left to right and right to left. 
         [0033]    b) Two A2 CIU units, on separate R143 units, will always be connected to two opposite networks: left to right and right to left. 
         [0034]    c) An A1 CIU and an A2 CIU, on the same train unit, will always be connected to the same network: left to left and right to right. 
         [0035]    Item c is used to determine which CIU units are part of the same train unit. 
         [0036]    The CIUs in each car build routing tables by sending out global discovery messages to all the nodes in the network in a conventional fashion. However, as can be seen in  FIG. 2 , the LonWorks protocol only applies in the case of a two-unit train. In the case of a three unit train a double cross over occurs. As a result an ambiguity arises as a result of similar nodes being connected to the same network sides in different train units. For example, in the example shown in  FIG. 2  the following nodes connections exist: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 A1, right side node in vehicle 1 
                 (node 1) 
               
               
                   
                 A2, right side node in vehicle 1 
                 (node 3) 
               
               
                   
                 A1, left side node in vehicle 2 
                 (node 6) 
               
               
                   
                 A2, left side node in vehicle 2 
                 (node 8) 
               
               
                   
                 A1, right side node in vehicle 3 
                 (node 9) 
               
               
                   
                 A2, right side node in vehicle 3 
                 (node 11) 
               
               
                   
                   
               
             
          
         
       
     
         [0037]    It will be seen that, for example, the right side node 3 in train unit 1, car A2, is also connected to right side nodes 9 and 11 in vehicle 3 as well as the right side node 1 in vehicle 1. In this train configuration the “fixed configuration” present in the two-unit train does not exist, and “global device discovery” messages cannot distinguish between the locations of certain network devices (i.e. A2, right side node in vehicle 1 and A2, right side node in vehicle 3 are in the same network). 
         [0038]    In order to overcome this problem, in an embodiment of the invention, in addition to global discovery messages as known in the prior art, each CIU broadcasts “local device discovery” messages, which are blocked by the gateways within the train unit containing the CIU. 
         [0039]    These messages are addressed in such a way that they are broadcast within a given vehicle (i.e. local broadcast), but are blocked by the vehicle&#39;s gateway devices from propagating to the network nodes in the other vehicles. This allows each vehicle to distinguish between the “local” and “remote” network nodes. With the additional knowledge of “local” vs. “remote” network nodes, network management for a 3-vehicle train is achieved. This information can be used to build a routing table to permit the CIUs to communicate with any desired node. 
         [0040]    The remaining network management system operates as in a conventional 1 or 2-unit train. 
         [0041]    The following table shows the existing prior art train logic for two-unit trains. In this table a node can be considered a network interface on the CIU. Each network interface has a unique ID. For the purpose of this example, they are numbered 1 to 8. For example, node 1 in vehicle 1 is locally connected to node 3 in vehicle (train unit) 1, otherwise (i.e. not locally) connected to nodes 6, 8 in vehicle 2, and not connected to nodes 2, 4 in vehicle 1 and nodes 5, 7 in vehicle 2. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 Local/Other Determination Table 
               
               
                   
                   
                   
                   
                   
                 (L = Local, R = Remote, 
               
               
                   
                   
                 Cab 
                 Network 
                 Network 
                 S = Same node, 
               
               
                 Vehicle 
                 Node 
                 (A1 or A2) 
                 (LS or RS) 
                 (1 or 2) 
                 — = Nodes not connected) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 A1 
                 RS 
                 1 
                 S 
                 — 
                 L 
                 — 
                 — 
                 O 
                 — 
                 O 
               
               
                   
                 2 
                 A1 
                 LS 
                 2 
                 — 
                 S 
                 — 
                 L 
                 O 
                 — 
                 O 
                 — 
               
               
                   
                 3 
                 A2 
                 RS 
                 1 
                 L 
                 — 
                 S 
                 — 
                 — 
                 O 
                 — 
                 O 
               
               
                   
                 4 
                 A2 
                 LS 
                 2 
                 — 
                 L 
                 — 
                 S 
                 O 
                 — 
                 O 
                 — 
               
               
                 2 
                 5 
                 A1 
                 RS 
                 2 
                 — 
                 O 
                 — 
                 O 
                 S 
                 — 
                 L 
                 — 
               
               
                   
                 6 
                 A1 
                 LS 
                 1 
                 O 
                 — 
                 O 
                 — 
                 — 
                 S 
                 — 
                 L 
               
               
                   
                 7 
                 A2 
                 RS 
                 2 
                 — 
                 O 
                 — 
                 O 
                 L 
                 — 
                 S 
                 — 
               
               
                   
                 8 
                 A2 
                 LS 
                 1 
                 O 
                 — 
                 O 
                 — 
                 — 
                 L 
                 — 
                 S 
               
             
          
           
               
                   
                 Vehicle 
                 1 
                 2 
               
             
          
           
               
                   
                 Node 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
               
               
                   
                 A1 or A2 
                 A1 
                 A1 
                 A2 
                 A2 
                 A1 
                 A1 
                 A2 
                 A2 
               
               
                   
                 LS or RS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
               
               
                   
                 1 or 2 
                 1 
                 2 
                 1 
                 2 
                 2 
                 1 
                 2 
                 1 
               
               
                   
                   
               
             
          
         
       
     
         [0042]    A1 or A2 Indicates in which car a node is located. This information is provided by discrete input/output (I/O) to the CIU. LS or RS indicates to which network a node is located, within a given unit. This information is provided by discrete I/O to the CIU. The 1 or 2 is a number given to the network that connects half of the nodes. If the numbers are different the nodes are not physically connected and therefore cannot communicate. The “Local Other” determination matrix uses a user defined function called “Local Other( )”. 
         [0043]    A three-unit train connected in accordance with the prior art would employ the following logic. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 Local/Other Determination Table 
               
               
                   
                   
                 Cab 
                 Network 
                 Network 
                 (L = Local, R = Remote, S = Same node, 
               
               
                 Vehicle 
                 Node 
                 (A1 or A2) 
                 (LS or RS) 
                 (1 or 2) 
                 — = Nodes not connected) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 A1 
                 RS 
                 1 
                 S 
                 — 
                 L 
                 — 
                 — 
                 O 
                 — 
                 O 
                 S 
                 — 
                 L 
                 — 
               
               
                   
                 2 
                 A1 
                 LS 
                 2 
                 — 
                 S 
                 — 
                 L 
                 O 
                 — 
                 O 
                 — 
                 — 
                 S 
                 — 
                 L 
               
               
                   
                 3 
                 A2 
                 RS 
                 1 
                 L 
                 — 
                 S 
                 — 
                 — 
                 O 
                 — 
                 O 
                 L 
                 — 
                 S 
                 — 
               
               
                   
                 4 
                 A2 
                 LS 
                 2 
                 — 
                 L 
                 — 
                 S 
                 O 
                 — 
                 O 
                 — 
                 — 
                 L 
                 — 
                 S 
               
               
                 2 
                 5 
                 A1 
                 RS 
                 2 
                 — 
                 O 
                 — 
                 O 
                 S 
                 — 
                 L 
                 — 
                 — 
                 O 
                 — 
                 O 
               
               
                   
                 6 
                 A1 
                 LS 
                 1 
                 O 
                 — 
                 O 
                 — 
                 — 
                 S 
                 — 
                 L 
                 O 
                 — 
                 O 
                 — 
               
               
                   
                 7 
                 A2 
                 RS 
                 2 
                 — 
                 O 
                 — 
                 O 
                 L 
                 — 
                 S 
                 — 
                 — 
                 O 
                 — 
                 O 
               
               
                   
                 8 
                 A2 
                 LS 
                 1 
                 O 
                 — 
                 O 
                 — 
                 — 
                 L 
                 — 
                 S 
                 O 
                 — 
                 O 
                 — 
               
               
                 3 
                 9 
                 A1 
                 RS 
                 1 
                 S 
                 — 
                 L 
                 — 
                 — 
                 O 
                 — 
                 O 
                 S 
                 — 
                 L 
                 — 
               
               
                   
                 10 
                 A1 
                 LS 
                 2 
                 — 
                 S 
                 — 
                 L 
                 O 
                 — 
                 O 
                 — 
                 — 
                 S 
                 — 
                 L 
               
               
                   
                 11 
                 A2 
                 RS 
                 1 
                 L 
                 — 
                 S 
                 — 
                 — 
                 O 
                 — 
                 O 
                 L 
                 — 
                 S 
                 — 
               
               
                   
                 12 
                 A2 
                 LS 
                 2 
                 — 
                 L 
                 — 
                 S 
                 O 
                 — 
                 O 
                 — 
                 — 
                 L 
                 — 
                 S 
               
             
          
           
               
                   
                 Vehicle 
                 1 
                 2 
                 3 
               
             
          
           
               
                   
                 Node 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
               
               
                   
                 A1 or A2 
                 A1 
                 A1 
                 A2 
                 A2 
                 A1 
                 A1 
                 A2 
                 A2 
                 A1 
                 A1 
                 A2 
                 A2 
               
               
                   
                 LS or RS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
               
               
                   
                 1 or 2 
                 1 
                 2 
                 1 
                 2 
                 2 
                 1 
                 2 
                 1 
                 1 
                 2 
                 1 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0044]    As shown above, the local/other determination “overlaps” on units 1 and 3, which will cause ambiguity issues for routing messages. For example, if the (A1,RS) interface in Unit 1 wants to send a message to the (A2, RS) in unit 1, it will not be able to determined whether this is node ID 3 or 11. For a three-vehicle train, the above shows there are routing issues for the outer units. 
         [0045]    The following table shows the enhanced logic implemented in a three or more unit train in accordance with an embodiment of the invention. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Cab 
                   
                   
                 Local/Other Determination Table 
               
               
                   
                   
                 (A1 or  
                 Network 
                 Network 
                 (L = Local, R = Remote, S = Same node, 
               
               
                 Vehicle 
                 Node 
                 A2) 
                 (LS or RS) 
                 (1 or 2) 
                 — = Nodes not connected) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 A1 
                 RS 
                 1 
                 S 
                 — 
                 L 
                 — 
                 — 
                 OM 
                 — 
                 OM 
                 OE 
                 — 
                 OE 
                 — 
               
               
                   
                 2 
                 A1 
                 LS 
                 2 
                 — 
                 S 
                 — 
                 L 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 OE 
                 — 
                 OE 
               
               
                   
                 3 
                 A2 
                 RS 
                 1 
                 L 
                 — 
                 S 
                 — 
                 — 
                 OM 
                 — 
                 OM 
                 OE 
                 — 
                 OE 
                 — 
               
               
                   
                 4 
                 A2 
                 LS 
                 2 
                 — 
                 L 
                 — 
                 S 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 OE 
                 — 
                 OE 
               
               
                 2 
                 5 
                 A1 
                 RS 
                 2 
                 — 
                 OM 
                 — 
                 OM 
                 S 
                 — 
                 L 
                 — 
                 — 
                 OM 
                 — 
                 OM 
               
               
                   
                 6 
                 A1 
                 LS 
                 1 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 S 
                 — 
                 L 
                 OM 
                 — 
                 OM 
                 — 
               
               
                   
                 7 
                 A2 
                 RS 
                 2 
                 — 
                 OM 
                 — 
                 OM 
                 L 
                 — 
                 S 
                 — 
                 — 
                 OM 
                 — 
                 OM 
               
               
                   
                 8 
                 A2 
                 LS 
                 1 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 L 
                 — 
                 S 
                 OM 
                 — 
                 OM 
                 — 
               
               
                 3 
                 9 
                 A1 
                 RS 
                 1 
                 OE 
                 — 
                 OE 
                 — 
                 — 
                 OM 
                 — 
                 OM 
                 S 
                 — 
                 L 
                 — 
               
               
                   
                 10 
                 A1 
                 LS 
                 2 
                 — 
                 OE 
                 — 
                 OE 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 S 
                 — 
                 L 
               
               
                   
                 11 
                 A2 
                 RS 
                 1 
                 OE 
                 — 
                 OE 
                 — 
                 — 
                 OM 
                 — 
                 OM 
                 L 
                 — 
                 S 
                 — 
               
               
                   
                 12 
                 A2 
                 LS 
                 2 
                 — 
                 OE 
                 — 
                 OE 
                 OM 
                 — 
                 OM 
                 — 
                 — 
                 L 
                 — 
                 S 
               
             
          
           
               
                   
                 Vehicle 
                 1 
                 2 
                 3 
               
             
          
           
               
                   
                 Node 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
               
               
                   
                 A1 or A2 
                 A1 
                 A1 
                 A2 
                 A2 
                 A1 
                 A1 
                 A2 
                 A2 
                 A1 
                 A1 
                 A2 
                 A2 
               
               
                   
                 LS or RS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
                 RS 
                 LS 
               
               
                   
                 1 or 2 
                 1 
                 2 
                 1 
                 2 
                 2 
                 1 
                 2 
                 1 
                 1 
                 2 
                 1 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0046]    In this logic there are now four node designations: S=Same; L=Local; OM=Other Middle; OE=Other End. In this way the ambiguity is resolved. 
         [0047]    In accordance with an embodiment of the invention the following procedure is performed as an initialization step:
       a) All nodes wake up start in the START mode.   b) Node 2 is the first to wake up.   c) Node 2 broadcasts a WU (Wake-up message) on the network but no node is there to receive it. Node 2 starts the Waiting End (WE) timer and switches into the WAIT mode.   d) Node 3 wakes up.   e) Node 3 broadcasts a WU. Node 3 starts a WE timer and switches into the WAIT mode.   f) Node 2 receives the WU from node 3:
           1) The countdown is stopped.   2) The countdown is set to WE—(quantity of WU received*(WE/10)). The “quantity of WUs received” is limited to eight for the purpose of computing the countdown value.   3) The waiting resumes.   
           g) Step e. is repeated for each new node waking-up.   h) Step f. is repeated by all nodes for each new WU received.   i) When no more WUs are broadcasted, the first node that wakes up (node 2) sets its WE timer to the lowest value following the last WU. It is the one to timeout first:   1) Node 2 switches into the ELECTION mode.   2) Node 2 broadcasts an Elections Occurring (EO).   3) Node 2 sends a global ping (GP) to node 1 to make sure it is alive, because it is going to be the next master. If node 2 is going to be the master, no ping will be sent. Note that the election node selects the node with the lowest Neuron ID not in a middle unit to be the master (that is node 1).   4) The timer Elected Ping Frequency (EPF) is started. If there is no answer, another node will be pinged.   5) Node 1 replies to node 2 with a PA (ping answer).       
 
         [0065]    6) Node 2 selects node 1 as master and broadcasts an Elected Master (EM)1 to elect it. It selects the node with the lowest Neuron ID to be the master.
       7) Node 1 switches into the MASTER mode and starts the Master Table Transmit (MTT) timer.   8) Node 2 sends a TT (Table Transmit) message to node 1 (master).   9) Node 1, if required (i.e. the train is 3 or more units in size), sends a local ping to each node on its network side in order to determine which nodes are local and which nodes are in the other end vehicle.   10) Node 1 builds the routing table and broadcasts a TT message.       
 
         [0070]    Messages over the CBTC network are sent using the Neuron ID (left or right side network) or in broadcast mode. 
         [0071]    For messages to go through the LonWorks gateway the subnet is set at “2” and the message length is not be longer than 32 bytes. All messages with the exception of the local ping (LP) message use these settings. The LP message uses a subnet of “3” to prevent it passing through the gateway. 
         [0072]    The ping message is used to find out whether a node is connected to the network and is working properly. This message may be global (subnet equal to “2”) or local (subnet equal to “3”) and is sent periodically by the master node to all nodes in the network. This process is used by the master to maintain the node table up to date. It is also used by an election node to find a working/connected node. The slave nodes require to be pinged at regular intervals by the master node. Nodes that are not pinged will elect a new master. 
         [0073]    The information received from the ping messages is then used to build routing tables at the Otis, which can then be used for subsequently addressing messages to an intended destination. 
         [0074]    The structure of a typical ping message is: 
         [0000]    
       
         
               
             
               
               
             
               
             
               
               
             
           
               
                   
               
             
             
               
                 MESSAGE ATTRIBUTES 
               
             
          
           
               
                 Service type 
                 Unacknowledged 
               
               
                 Address type 
                 Neuron ID 
               
               
                 Total message length in bytes 
                 14 
               
             
          
           
               
                 MESSAGE CONTENT 
               
             
          
           
               
                 Code 
                 10 
               
               
                 Data 
                 Node information of the source 
               
               
                   
                 (7 bytes) 
               
               
                   
                 Node information of the destination 
               
               
                   
                 (7 bytes) 
               
               
                   
               
             
          
         
       
     
         [0075]    In response to a ping message, the nodes send back a ping acknowledge message with the following structure: 
         [0000]    
       
         
               
             
               
               
             
               
             
               
               
             
           
               
                   
               
             
             
               
                 MESSAGE ATTRIBUTES 
               
             
          
           
               
                 Service type 
                 Unacknowledged 
               
               
                 Address type 
                 Neuron ID 
               
               
                 Total message length in bytes 
                 11 
               
             
          
           
               
                 MESSAGE CONTENT 
               
             
          
           
               
                 Code 
                 11 
               
               
                 Data 
                 Node information of the sender (7 bytes) 
               
               
                   
                 Number of nodes in the node table of the 
               
               
                   
                 sender (1 bytes) 
               
               
                   
                 Checksum of the node table of the sender 
               
               
                   
                 (2 bytes) 
               
               
                   
                 Number of statistics (1 byte); future 
               
               
                   
                 provision; always 0 (1 byte) 
               
               
                   
               
             
          
         
       
     
         [0076]    It will thus be seen that embodiments of the invention expand the capabilities of a LonWorks™ or similar network to allow for three train or more units to be connected in tandem, something which is not possible with in the original network design. It will be understood that the logic may be different for trains consisting of more than three train units. One skilled in the art will be able to configure the logic for more than three train units following the principles of the invention described above. 
         [0077]    The described communication network thus allows the CBTC system to provide full on-board automatic train protection (ATP) for a train consisting of three train units, an important advantage that was not possible in the prior art. 
         [0078]    It should be understood that the logic described herein applies to up to three train units. However, one skilled in the art will recognize that by modifying the logic, the concept of using local discovery messages can be applied to trains consisting of more than three train units.