Network system implementing a plurality of switching devices to block passage of a broadcast signal

To provide a network system including a network constructed by combining a plurality of switching devices. The network includes a first partial network including switching devices and a second partial network that is formed outside the first partial network and includes switching devices. The switching device in the first partial network connected to the second partial network blocks passage of a broadcast signal that is transmitted from a terminal device and that has a specific logical port number as transmission information at a physical port.

FIELD

The present invention relates to a network system, and more particularly to a network system constructed in a train.

BACKGROUND

TCP/IP is a well known communication protocol used between devices (see, for example, Non Patent Literature 1). In the TCP/IP, an IP address allocated to each device is used to specify a destination and a source in order to perform communication. It should be noted that there is, for example, a limited broadcast address as a unique IP address. When transmission data is transmitted specifying its destination as a limited broadcast address, the transmission data reaches all the devices in a network.

Generally, a method of transmitting transmission data to all the devices in a network is referred to as a “broadcast”. The range over which the broadcast can reach is referred to as a “broadcast domain”.

CITATION LIST

Non Patent Literature

SUMMARY

Technical Problem

When a broadcast is used, all the devices in the network receive broadcast data, so that it is difficult to form a subgroup including a plurality of devices in a broadcast domain and broadcast data to the subgroup. For example, in a network in a train formed with a plurality of vehicles, it becomes difficult to divide respective devices in the network into groups corresponding to respective cars in which each device is incorporated and to realize both a broadcast to each group and a broadcast to all the devices in the network.

The present invention has been achieved to solve the above problems, and an object of the present invention is to provide a network system that can limit the range of access of a broadcast having a specific condition.

Solution to Problem

In order to solve the aforementioned problems, a network system including a network constructed by combining a plurality of switching devices according to one aspect of the is configured in such a manner as to include a first subnetwork and a second subnetwork that is formed outside the first subnetwork, and at least one of a switching device in the first subnetwork connected to the second subnetwork and a switching device in the second subnetwork connected to the first subnetwork blocks passage of a broadcast signal that includes a specific logical port number as transmission information.

Advantageous Effects of Invention

According to the present invention, it is possible to limit the range of access of a broadcast to within a first subnetwork or a second subnetwork.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of a network system according to the present invention will be explained below in detail and with reference to the accompanying drawings. The present invention is not limited to the embodiments.

First Embodiment

FIG. 1is an example of a configuration of a network system according to a first embodiment. The network system according to the present embodiment includes, for example, switching devices1to5that are Ethernet® switches, a terminal device6, and apparatuses7to10.

The switching device1is connected to the switching device2. The switching device2is connected to the switching devices3and4. The switching device4is connected to the switching device5. A network is constructed by combining the switching devices1to3in this manner. The network includes a subnetwork formed of the switching devices1to3in an area11and a subnetwork formed of the switching devices4and5. The terminal device6is connected to the switching device1, the apparatus7is connected to the switching device1, the apparatus8is connected to the switching device3, the apparatus9is connected to the switching device4, and the apparatus10is connected to the switching device5. The switching devices1to5each include, for example, five physical ports, and connections between the switching devices are established via these physical ports.

An IP address is attached to the terminal device6, and the terminal device6can perform IP communication. Similarly, an IP address is attached to each of the apparatuses7to10, and each of the apparatuses7to10can perform IP communication. As explained below, in the present embodiment, the terminal device6is distinguished from the apparatuses7to10as an apparatus that can perform broadcasting. However, the apparatuses7to10can also have a configuration that can perform broadcasting.

FIG. 2is a schematic diagram of an example of a configuration of an IP signal to be used for IP communication by the terminal device6or the apparatuses7to10. The IP signal includes, for example, a transmission destination address, a transmission source address, a logical port number, and a data portion.

At the time of performing IP communication, when any one of the IP addresses of the terminal device6and the apparatuses7to10is specified as “transmission destination address”, the IP signal is transferred to the terminal device6or the apparatuses7to10having the corresponding IP address.

Broadcasting is explained next. When a broadcast is performed from the terminal device6, a broadcast address is specified as “transmission destination address”, and transmission data is transferred to all the apparatuses7to10in the network. In the present embodiment, a broadcast in which the range of access of the broadcast is limited to, for example, the subnetwork in the area11inFIG. 1is examined in addition to a broadcast in which all the apparatuses7to10are designated as a “destination”. The area11includes the switching devices1to3, the terminal device6, and the apparatuses7and8.

In the present embodiment, the following function is given to the switching device2to limit the range of access of the broadcast. That is, at a physical port12used for connecting to the switching device4outside the area11among the physical ports of the switching device2, the switching device2blocks passage of a broadcast signal having a specific logical port number (for example, a logical port number “4000”). In this case, the broadcast signal is an IP signal in which the broadcast address is specified as the transmission destination address. In contrast, the switching device2does not block passage of the broadcast signal having a logical port number other than the specific logical port number (for example, a logical port number “4001”), and it allows the broadcast signal to pass therethrough.

The operation is explained next. First, a case where the terminal device6specifies a broadcast address as a transmission destination address and the logical port number4000to transmit an IP signal to the network is considered. In this case, the IP signal is received by the switching device1, and the switching device1transmits the IP signal to the apparatus7via the physical port to which the apparatus7is connected, and it also transmits the IP signal to the switching device2via the physical port to which the switching device2is connected. After having received the IP signal via the physical port to which the switching device1is connected, the switching device2transmits the IP signal to the switching device3via the physical port to which the switching device3is connected, and determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is the broadcast signal, the switching device2determines whether the logical port number of the broadcast signal is4000. When it recognizes that the IP signal is the broadcast signal having the logical port number4000, the switching device2blocks the passage of the IP signal to outside the area11at the physical port12. The switching device3transmits the IP signal to the apparatus8via the physical port to which the apparatus8is connected. As a result, while the IP signal reaches the apparatuses7and8in the area, the IP signal does not reach the apparatuses9and10outside the area11.

In this manner, according to the present embodiment, by transmitting the broadcast signal having the logical port number4000from the terminal device6despite the transmission destination address being the broadcast address, the transmission range of the broadcast can be easily limited to the subnetwork within the area11.

A case where the terminal device6assumes the transmission destination address as a broadcast address and transmits an IP signal having, for example, the logical port number4001to the network is considered next. In this case, because passage of the broadcast signal is not blocked at any of the physical ports of the switching devices1to5, the IP signal is transmitted to all the apparatuses7to10in the network. That is, because the logical port number of the broadcast signal is different from4000, passage of the broadcast signal is not blocked even at the physical port12of the switching device2. As a result, all the apparatuses7to10receive the IP signal.

As explained above, in the present embodiment, in the subnetwork in the area11formed of the switching devices1to3and including the switching device1to which the terminal device6is connected, when having received a broadcast signal including the logical port number4000, which is a specific logical port number, as transmission information from the terminal device6, the switching device2that is directly connected to the switching device4in the subnetwork formed of the switching devices4and5outside the area11blocks passage of the broadcast signal at the physical port12to which the switching device4is connected.

Accordingly, in the present network system, by changing the logical port number of the broadcast signal, the broadcast domain can be designated as the entire network (when the logical port number4001is specified), or can be limited to the subnetwork in the area11(when the logical port number4000is specified).

Because the range of access of the broadcast can be limited by specifying, for example, a logical port number other than the transmission destination address to a specific value, while maintaining the broadcast address as the transmission destination address, the present embodiment is particularly useful when it is desired to limit the range of access of the broadcast after the network system is constructed. In this case, because the broadcast domain can be limited without changing any part of the IP address, the range of access of the broadcast can be set more flexibly and easily after the network system is constructed as compared with a case of using multicast or the like.

Furthermore, even when an apparatus is newly connected or disconnected in the network, there is an advantage in that there is no need to perform any system change with regard to limiting the broadcast domain.

Further, according to the present embodiment, the range of access of the broadcast can be limited without causing any increase in traffic.

Limiting the range of access of the broadcast is useful when, depending on the contents of the data portion of the transmission data, it is desired to transmit transmission data only to some part of the apparatuses without transmitting the transmission data to all the apparatuses in the network. For example, the present network system is suitable for a network system constructed in a train, and a specific example of such is explained in the following embodiment.

In the present embodiment, a broadcast signal having a specific logical port number and transmitted from the terminal device6is blocked at the physical port12of the switching device2. However, the broadcast signal can be blocked at a physical port among the physical ports of the switching device4to which the switching device2is connected. In this case, although the broadcast signal having a specific logical port number is transmitted from the switching device2to the switching device4via the physical port12, the switching device4blocks the broadcast signal from entering the subnetwork formed of the switching devices4and5. By blocking the broadcast signal in this manner, the broadcast domain can be limited within the area11as in the present embodiment.

Furthermore, in the present embodiment, it has been explained that the logical port number to be blocked at the physical port12is4000as an example. However, values other than4000can be used. In addition, it is also possible to specify a plurality of logical port numbers and to block the broadcast signal having these logical port numbers.

Further, it has been assumed that the area11includes the switching devices1to3, for example. However, it is possible to use an arbitrary area including at least one switching device and one apparatus. That is, it can be an area that includes a part of all the apparatuses in a part of the entire network.

Second Embodiment

FIG. 3is an example of a configuration of a network system according to a second embodiment, and it is specifically a configuration diagram of a network system constructed in a train in which a plurality of vehicles are connected. InFIG. 3, as an example, the train has a formation of three or more cars and the configurations of a first car and a second car are shown as examples. However, vehicles other than these cars can be configured in the same manner. The train can have a two-car formation having the configuration exemplified inFIG. 3.

InFIG. 3, the network system according to the present embodiment includes switching devices21to24, terminal devices25and26, and apparatuses27to29. The switching devices21and22, the terminal device25, and the apparatuses27and28are incorporated in the first car, and the switching devices23and24, the terminal device26, and the apparatus29are incorporated in the second car. The first car is the lead vehicle or the last vehicle, and the second car is a vehicle in the middle. Similarly to the first embodiment, the switching devices21to24are the Ethernet® switches, for example. In the present embodiment, one terminal device is incorporated in each of the cars. The terminal devices25and26are, for example, train-information management devices. The train-information management device is a device that collects and manages train information and that can monitor the operating state of apparatuses incorporated in a train and can control operations of those apparatuses individually.

The switching device21is connected to the switching device22, the switching device22is connected to the switching device23, and the switching device23is connected to the switching device24. That is, the switching devices21to24are connected in this order, for example, in a daisy chain configuration.

In the first car, the terminal device25is connected to the switching device21, and the apparatuses27and28are connected to the switching device22. In the first car, a subnetwork constituted by the switching devices21and22is formed. In the second car, the terminal device26is connected to the switching device23, and the apparatus29is connected to the switching device23. In the second car, a subnetwork constituted by the switching devices23and24is formed. The subnetwork in the first car and the subnetwork in the second car are connected to each other by the switching devices22and23. Although not shown, the same subnetwork is formed in the third car.

The present embodiment is configured to realize both broadcasting to the entire train and broadcasting limited to the inside of the respective cars. Specifically, the network is constructed so that a broadcast signal having a specific logical port number (for example, the logical port number4000) is blocked at the respective physical ports used for mutual connection of the switching device22in the first car and the switching device23in the second car. That is, inFIG. 3, passage of the broadcast signal having the logical port number4000is blocked at a physical port50among the physical ports of the switching device22, which is used for connection to the switching device23. Furthermore, passage of the broadcast signal having the logical port number4000is blocked at a physical port51among the physical ports of the switching device23, which is used for connection to the switching device22. Further, passage of the broadcast signal having the logical port number4000is blocked at a physical port54of the physical ports of the switching device24, which is used for connection to a switching device (not shown) in the third car.

The operation of the present embodiment is explained next. The terminal device25specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information of the first car (information indicating the first car) in a data portion to transmit the IP signal regularly to a network. The configuration of the transmission data is identical to the one shown inFIG. 2. In this case, the IP signal is received by the switching device21via a physical port60, and the switching device21transmits the IP signal to the switching device22via a physical port48to which the switching device22is connected. Upon reception of the IP signal via a physical port49to which the switching device21is connected, the switching device22transmits the IP signal to the apparatuses27and28via physical ports62and64to which the apparatuses27and28are connected, and it determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device22determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device22blocks passage of the IP signal into the subnetwork in the second car at the physical port50to which the switching device23is connected.

In this manner, while the IP signal is transferred to the switching devices21and22and the apparatuses27and28connected to the switching device22, the IP signal is not transferred to the switching device23. As a result, the IP signal is not transferred to the second car, and is not transferred to the third and subsequent cars either. Accordingly, the range of access of the broadcast is limited to the first car, regarding the broadcast signal having the logical port number4000transmitted from the terminal device25.

The terminal device26specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information on the second car (information indicating the second car) in a data portion to transmit the IP signal regularly to a network. In this case, the IP signal is received by the switching device23via a physical port68, and the switching device23transmits the IP signal to the switching device24via a physical port52to which the switching device24is connected, transmits the IP signal to the apparatus29via a physical port70to which the apparatus29is connected, and determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device23determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device23blocks passage of the IP signal into the subnetwork in the first car at the physical port51to which the switching device22is connected.

The switching device24receives the IP signal from the switching device23via a physical port53, and because the IP signal is the broadcast signal, determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device24blocks passage of the IP signal at the physical port54connected to a switching device (not shown) in the third car.

In this manner, while the IP signal is transferred to the switching devices23and24and the apparatus29connected to the switching device23, the IP signal is not transferred to the switching device22in the first car and a switching device (not shown) in the third car. As a result, the IP signal is transferred neither to the first car, nor to the third and subsequent cars. In this manner, the range of access of the broadcast of the broadcast signal having the logical port number4000transmitted from the terminal device26is limited to the inside of the second car. According to the same configuration, the range of access of the broadcast can also be limited to the inside of each of the third and subsequent cars. That is, in the switching devices mutually connected between the adjacent cars, it will be sufficient if the passage of the broadcast signal having a specific logical port number is blocked.

As described above, the apparatuses27and28incorporated in the first car receive only the broadcast signal transmitted by the terminal device25among the broadcast signals having the logical port number4000. Because the apparatuses27and28can acquire the information on the first car by reading the content of the data portion of the broadcast signal respectively, they can determine that they themselves are installed in the first car.

The apparatus29incorporated in the second car receives only the broadcast signal transmitted by the terminal device26among the broadcast signals having the logical port number4000. Because the apparatus29can acquire the information on the second car by reading the contents of the data portion of the broadcast signal, it can determine that itself is installed in the second car. The same applies to the third and subsequent cars.

When the terminal device25specifies a broadcast address as the transmission destination address, and the logical port number as4001which is different from4000to transmit the IP signal to the network, as in the first embodiment, because passage of the broadcast signal is not blocked at any of the physical ports of the switching devices21to24, the IP signal is transmitted to all the apparatuses27to29, the terminal device26and the like in the network. As a result, the apparatuses27to29, the terminal device26, and the like receive the IP signal.

When the terminal device26specifies a broadcast address as the transmission destination address, and the logical port number as4001which is different from4000to transmit the IP signal to the network, because passage of the broadcast signal is not blocked at any of the physical ports of the switching devices21to24, the IP signal is transmitted to all the apparatuses27to29, the terminal device25and the like in the network. As a result, the apparatuses27to29, the terminal device25, and the like receive the IP signal.

As explained above, in the present embodiment, in the subnetwork in the first car, when receiving the broadcast signal including the logical port number4000, which is the specific logical port number, from the terminal device25, the switching device22connected to the subnetwork in the second car blocks passage of the broadcast signal into the subnetwork in the second car. Also in the network in the second car, when receiving the broadcast signal including the logical port number4000from the terminal device26, the switching device23connected to the subnetwork in the first car blocks passage of the broadcast signal into the subnetwork in the first car. Further, when receiving the broadcast signal including the logical port number4000from the terminal device26, the switching device24connected to the subnetwork in the third car blocks passage of the broadcast signal into the subnetwork in the third car at the physical port54connected to the subnetwork in the third car.

Accordingly, in the present network system, by switching the logical port number of the broadcast signal, the broadcast domain can be specified as the entire network in the train (when the logical port number4001is specified), or the broadcast domain can be limited to the subnetwork in the respective cars (when the logical port number4000is specified).

According to the present embodiment, the broadcast domain can be divided into respective vehicles.

According to the present embodiment, the apparatuses installed in each of the cars can, after receiving a broadcast signal having the logical port number4000transmitted from the terminal device, determine in which car they themselves are installed by referring to the data portion of the broadcast signal.

Further, in the present embodiment, at the physical ports50and51used for connection between the switching devices22and23that connect the vehicles, a broadcast signal having a specific logical port number is blocked, and the range of access of the broadcast signal is limited to each car. However, when there is a division of functions in the vehicle, the range of access of the broadcast can be further limited within that vehicle. For example, inFIG. 3, when the whole network configuration of the first and second cars is incorporated into one vehicle, divided regions of two broadcast domains are formed in one vehicle.

When a plurality of continuous vehicles are integrated as a managing target, a limited region of the broadcast domain can be set with respect to these vehicles. For example, inFIG. 3, when blocking of the broadcast signal having the specific logical port number is performed by the switching device24and a switching device (not shown) in the third car instead of being performed by the switching devices22and23, a broadcast limited to the inside of the first and second cars can be realized.

In the present embodiment, when the broadcast signal including the specific logical port number as transmission information transmitted from the terminal device25is received, the switching device22blocks passage of the broadcast signal into the subnetwork in the second car at the physical port50. When the broadcast signal including the specific logical port number as the transmission information transmitted from the terminal device26is received, the switching device23blocks the passage of the broadcast signal into the subnetwork in the first car at the physical port51, and blocks the passage of the broadcast signal into the subnetwork in the third car is further blocked at the physical port54of the switching device24. However, the broadcast signal including the specific logical port number transmitted from the terminal device26can be blocked from entering the subnetwork in the first car at the physical port50of the switching device22, the broadcast signal including the specific logical port number transmitted from the terminal device25can be blocked from entering into the subnetwork in the second car at the physical port51of the switching device23, and the broadcast signal including the specific logical port number transmitted from a terminal device (not shown) in the third car can be blocked from entering the subnetwork in the second car at the physical port54of the switching device24.

That is, when the broadcast signal including the specific logical port number as transmission information transmitted from the terminal device26is received, the switching device22can block passage of the broadcast signal into the subnetwork in the first car at the physical port50. When the broadcast signal including the specific logical port number as the transmission information transmitted from the terminal device25is received, the switching device23can block passage of the broadcast signal into the subnetwork in the second car at the physical port51. When the broadcast signal including the specific logical port number as the transmission information transmitted from a terminal device (not shown) in the third car is received, the switching device23can block passage of the broadcast signal into the subnetwork in the second car at the physical port54of the switching device24. Even in this case, the range of access of the broadcast can be limited to each car, and thus effects identical to those of the present embodiment can be achieved.

Furthermore, in the present embodiment, a case where both the switching device22in the first car and the switching device23in the second car block the broadcast signal having a specific logical port number has been explained. However, a configuration in which the broadcast signal is blocked by any one of the switching devices22and23can be also applied. For example, when the broadcast signal including the specific logical port number as the transmission information transmitted from the terminal device25is received, the switching device22can block passage of a broadcast signal into the subnetwork in the second car at the physical port50, and when a broadcast signal including the specific logical port number as the transmission information transmitted from the terminal device26is received, the switching device22can block passage of a broadcast signal into the subnetwork in the first car at the physical port50. With this configuration, even without giving a blocking function to the switching device23, a broadcast from the terminal device25does not reach the second car and a broadcast from the terminal device26does not reach the first car. The same applies to the switching device24and a switching device (not shown) in the third car. Accordingly, also in this case, effects identical to those of the present embodiment can be achieved.

Further, when the terminal device incorporated in each vehicle is set to be a train-information management device, the train-information management device in each vehicle can transmit the train information of the vehicle by a broadcast only to the apparatus in its own vehicle, by using a broadcast signal having a specific logical port number.

Configurations, operations, and effects of the present embodiment other than those described above are as explained in the first embodiment.

Third Embodiment

FIG. 4is an example of a configuration of a network system according to the third embodiment, and it is specifically a configuration diagram of a network system constructed in a train in which a plurality of vehicles are connected. InFIG. 4, the same reference sign refers to the same constituent elements shown inFIG. 3, and thus only constituent elements different from those shown inFIG. 3are explained.

InFIG. 4, a terminal device30is connected to the switching device22via a physical port63, and a terminal device31is connected to the switching device24via a physical port72. The terminal device30is incorporated in the first car and the terminal device31is incorporated in the second car. In the present embodiment, two terminal devices are incorporated in each vehicle. The terminal devices25,26,30, and31are, for example, train-information management devices.

Similarly to the second embodiment, the present embodiment is configured such that both broadcast over the entire train and broadcasts limited to each car are realized. That is, at the physical port50used for connection to the switching device23among the physical ports of the switching device22, passage of a broadcast signal having the logical port number4000is blocked. At the physical port51used for connection to the switching device22among the physical ports of the switching device23, passage of a broadcast signal having the logical port number4000is blocked. At the physical port54used for connection to a switching device (not shown) in the third car among the physical ports of the switching device24, passage of a broadcast signal having the logical port number4000is blocked.

The operation of the present embodiment is explained next. The terminal device25specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information on the first car (information indicating the first car) in a data portion to transmit the IP signal regularly to a network. The configuration of the transmission data is identical to that shown inFIG. 2. In this case, the IP signal is received by the switching device21, and the switching device21transmits the IP signal to the switching device22via the physical port48to which the switching device22is connected. Upon reception of the IP signal via the physical port49to which the switching device21is connected, the switching device22transmits the IP signal to the apparatuses27and28via the physical ports62and64to which the apparatuses27and28are connected, transmits the IP signal to the terminal device30via the physical port63to which the terminal device30is connected, and determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device22determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device22blocks passage of the IP signal into the subnetwork in the second car at the physical port50to which the switching device23is connected.

The terminal device30specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information of the first car (information indicating the first car) in a data portion to transmit the IP signal regularly to the network. In this case, the IP signal is received by the switching device22, and the switching device22transmits the IP signal to the switching device21via the physical port49to which the switching device21is connected, transmits the IP signal to the apparatuses27and28via the physical ports62and64, and transmits the IP signal to the terminal device30via the physical port63. The switching device22then determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device22determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device22blocks passage of the IP signal into the subnetwork in the second car at the physical port50to which the switching device23is connected. Further, the switching device21transmits the IP signal to the terminal device25via the physical port60.

The terminal device26specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information on the second car (information indicating the second car) in a data portion to transmit the IP signal regularly to a network. In this case, the IP signal is received by the switching device23via the physical port68, and the switching device23transmits the IP signal to the switching device24via the physical port52to which the switching device24is connected, transmits the IP signal to the apparatus29via the physical port70to which the apparatus29is connected, and determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device23determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device23blocks passage of the IP signal into the subnetwork in the first car at the physical port51to which the switching device22is connected.

The switching device24receives the IP signal from the switching device23via the physical port53, and transmits the IP signal to the terminal device31via the physical port72. Because the IP signal is a broadcast signal, the switching device24determines whether the logical port number of the IP signal is4000. When recognizing that the logical port number of the IP signal is4000, the switching device24blocks passage of the IP signal into the subnetwork in the third car at the physical port54to which a switching device (not shown) in the third car is connected.

The terminal device31specifies a broadcast address as the transmission destination address of an IP signal, and the logical port number as4000, and sets information on the second car (information indicating the second car) in a data portion to transmit the IP signal regularly to a network. In this case, the IP signal is received by the switching device24via the physical port72, and the switching device24transmits the IP signal to the switching device23via the physical port53to which the switching device23is connected. Because the IP signal is a broadcast signal, the switching device24determines whether the logical port number of the IP signal is4000. When recognizing that the logical port number of the IP signal is4000, the switching device24blocks passage of the IP signal into the subnetwork in the third car at the physical port54to which a switching device (not shown) in the third car is connected.

When the IP signal is received by the switching device23via the physical port52to which the switching device24is connected, the switching device23transmits the IP signal to the apparatus29via the physical port70to which the apparatus29is connected, transmits the IP signal to the terminal device26via the physical port68to which the terminal device26is connected, and determines whether the logical port number of the IP signal is4000. That is, when the received IP signal is a broadcast signal, the switching device23determines whether the logical port number is4000. When recognizing that the logical port number of the IP signal is4000, the switching device23blocks passage of the IP signal into the subnetwork in the first car at the physical port51to which the switching device22is connected.

In this manner, the apparatuses27and28incorporated in the first car receive only broadcast signals transmitted from the terminal devices25and30among the broadcast signals having the logical port number4000. Further, because the apparatuses27and28can acquire information on the first car respectively by reading the contents of the data portion of the broadcast signal, the apparatuses27and28can determine that they themselves are installed in the first car.

Furthermore, when the terminal devices25and30form a redundant system (in this case, a dual system), even if any one of the terminal devices25and30has a defect, as long as the defect is only in one system, the apparatuses27and28can receive broadcast signals from the terminal device25or30to determine the number of the car in which the apparatuses27and28are incorporated. Further, even if a malfunction occurs in a transmission path from the terminal device25, as long as a transmission path from the terminal device30is normal, the apparatuses27and28can receive the broadcast signal from the terminal device30to determine the number of the car in which the apparatuses27and28are incorporated. Furthermore, even if a malfunction occurs in the transmission path from the terminal device30, as long as the transmission path from the terminal device25is normal, the apparatuses27and28can receive the broadcast signal from the terminal device25to determine the number of the car in which the apparatuses27and28are incorporated.

Similarly, the apparatus29incorporated in the second car receives only broadcast signals transmitted from the terminal devices26and31among the broadcast signals having the logical port number4000. Further, because the apparatus29can acquire information on the second car by reading the contents of the data portion of the broadcast signal, the apparatus29can determine that the apparatus itself is installed in the second car.

Furthermore, when the terminal devices26and31form a redundant system (in this case, a dual system), even if any of the terminal devices26and31has a defect, as long as the defect is only in one system, the apparatus29can receive the broadcast signal from the terminal device26or31to determine the number of the car in which the apparatus29is incorporated. Further, even if a malfunction occurs in a transmission path from the terminal device26, as long as a transmission path from the terminal device31is normal, the apparatus29can receive the broadcast signal from the terminal device31to determine the number of the car in which the apparatus29is incorporated. Furthermore, even if a malfunction occurs in the transmission path from the terminal device31, as long as the transmission path from the terminal device26is normal, the apparatus29can receive broadcast signals from the terminal device26to determine the number of the car in which the apparatus29is incorporated.

Configurations, operations, and effects of the present embodiment other than those described above are identical to those explained in the second embodiment. Particularly, various blocking methods explained in the second embodiment can be similarly applicable to the present embodiment.

INDUSTRIAL APPLICABILITY

The present invention is useful as a system capable of limiting or dividing a broadcast domain of, for example, an Ethernet® network.

REFERENCE SIGNS LIST