JP2022181407A - Surveillance system and gateway - Google Patents

Abstract

To provide a monitoring system communication technique capable of applying an existing monitoring system without requiring a drastic change even when the system is mixed with another system on a new communication network.SOLUTION: A monitoring system (1) includes gateways (GX, GY) for each of sub-nets (X, Y) connected to devices (A, B, C) of the monitoring system. When each of the gateways (GX, GY) receives a first communication request whose transmission destination is a device connected to another sub-net from the device connected to its own sub-net, the monitoring system generates an inter-gateway communication request including contents of the first communication request, and transfers the request to a gateway of a transmission destination sub-net connected to the transmission destination device. When receiving an inter-gateway communication request from another gateway, the monitoring system generates a second communication request in which a transmission source address and a transmission destination address included in the inter-gateway communication request are converted into addresses used in its own sub-net, and transmits the request to its own sub-net.SELECTED DRAWING: Figure 1

Description

The present invention relates to surveillance system communication technology for data communication between devices connected to different subnets.

Large-scale facilities such as buildings, plants, and factories generally operate a monitoring system that remotely monitors and controls various equipment installed in the facility via a communication network. For example, in buildings, equipment such as lighting, air conditioning, crime prevention security, power meters, etc. in the building are centrally managed via a communication network, and BAS (Building Automation System) is used to monitor and control the equipment. is in operation. Further, in facilities such as plants and factories, a DCS (Distributed Control System) is operated to perform distributed control of various equipment installed in the facility via a communication network.

In monitoring systems such as BAS and DCS, IP networks have long been adopted as communication networks that serve as a basis for constructing monitoring systems. Also, as the communication protocol, UDP (User Datagram Protocol), which has a small overhead and is capable of broadcast communication, is mainly used. Layer 4 protocols include TCP (Transmission Control Protocol), which is similar to UDP. TCP is a connection-oriented communication method that exchanges a large number of control packets to achieve high reliability and optimized communication efficiency. Tend. On the other hand, UDP is a connectionless communication method and has low reliability because it does not exchange control packets.

JP 2004-253976 A

By the way, the configuration of the communication network that constructs these monitoring systems changes year by year, and there are cases where the existing monitoring system cannot be applied to the communication network as it is. As an example of such a case, the coexistence of other systems on the communication network restricts the broadcasting of the same packet to multiple destinations between devices in the monitoring system. I have a case. Also, existing surveillance systems may include devices intended for use on a single subnet.
In such a case, it is conceivable to employ a BBMD (BACnet Broadcast Management Device) as a communication control device that transfers broadcast packets to another subnet. However, in this case, since packets are transmitted by broadcast from the BBMD even in the destination subnet, it cannot be used when systems in which broadcast communication is restricted coexist.

In addition, Patent Document 1 proposes a method of providing multicast (Multicast: one-to-many communication) in an IP network where only unicast (unicast: one-to-one communication) is provided. It can also be applied to cases where However, according to this method, the communication mode in the destination subnet is limited to multicast, and it is necessary to install an address management server in addition to the packet conversion device in each subnet. Therefore, it is difficult to apply it to the case mentioned above.

The present invention is intended to solve such problems, and is a monitoring system communication that can be applied to an existing monitoring system without the need for major changes even when it is mixed with another system on a new communication network. The purpose is to provide technology.

In order to achieve such an object, a monitoring system according to the present invention comprises a plurality of devices connected to one of a plurality of subnets, and a plurality of gateways connected to each of the plurality of subnets, Each of the plurality of devices has an address used in its own subnet and an address used in another subnet, and each of the plurality of gateways is a device connected to its own subnet among the plurality of devices. and a second communication interface configured to perform data communication between a gateway connected to another subnet among the plurality of gateways When receiving a first communication request destined for a device connected to another subnet from a device connected to its own subnet, the content of the first communication request is included. When an inter-gateway communication request is generated and transferred to the gateway of the destination subnet to which the destination device is connected, and when the inter-gateway communication request is received from another gateway, it is included in the inter-gateway communication request It is configured to generate a second communication request in which the source address and destination address are converted to addresses used in its own subnet, and transmit the second communication request to its own subnet.

A gateway according to the present invention comprises a plurality of devices connected to one of a plurality of subnets, and a plurality of gateways connected to each of the plurality of subnets, and each of the plurality of devices is connected to its own subnet. said gateway used in a monitoring system having an address used and an address used in another subnet, said gateway used in said plurality of devices for performing data communication with a device connected to its own subnet; and a second communication interface configured to perform data communication between a gateway connected to another subnet among the plurality of gateways, and connected to its own subnet When a first communication request addressed to a device connected to another subnet is received from a device connected to another subnet, an inter-gateway communication request including the content of the first communication request is generated and sent to the destination. is transferred to the gateway of the destination subnet to which the device is connected, and when the inter-gateway communication request is received from another gateway, the source address and destination address included in the inter-gateway communication request are transferred to the self subnet and a control circuit configured to generate a second communication request converted into an address used in the and transmit it to its own subnet.

According to the present invention, it is possible to apply an existing monitoring system without requiring major changes even when it is mixed with another system on a new communication network.

FIG. 1 is a block diagram showing the configuration of a monitoring system. FIG. 2 is a block diagram showing the configuration of the gateway. FIG. 3 is a configuration example of the address conversion table of the gateway. FIG. 4 is another configuration example of the address conversion table of the gateway. FIG. 5 is a sequence diagram showing the operation (unicast) of the monitoring system. FIG. 6 is a sequence diagram showing the operation (broadcast) of the monitoring system.

Next, one embodiment of the present invention will be described with reference to the drawings.
[Monitoring system]
First, a monitoring system 1 according to this embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of a monitoring system.
This monitoring system 1 consists of a monitoring system such as BAS or DCS that is operated in large-scale facilities such as buildings, plants, and factories as a whole, and is provided with a plurality of subnets provided on a base IP network. there is

In the following, as shown in FIG. 1, two subnets consisting of subnet X (10) and subnet Y (20) are provided and are connected to each other via relay system R as an example. . The relay system R is composed of a communication network such as VPN (Virtual Private Network), FW (Firewall), router, etc., communication functions, and communication equipment. It should be noted that the number of subnets and connection form according to the present invention are not limited to this, and the present invention can be applied in the same manner as described below even with other numbers of subnets and other connection forms.

The address range "192.168.0.0 to 192.168.255.255 (hereinafter referred to as 192.168.*.*)" is assigned to subnet X, and devices A (11) and B (12) performing UDP communication and gateway GX (13 ) is connected. Subnet Y is assigned an address range of 172.16.0.0 to 172.16.255.255 (hereafter referred to as 172.16.*.*), and is connected to gateway GY (21) and device C (22) that perform UDP communication. It is In this embodiment, a case where UDP unicast (one-to-one communication) is performed between subnet X and subnet Y will be described as an example.

Device A is assigned a real address of 192.168.10.1 and an alternate address of 172.16.10.1, and device B is assigned a real address of 192.168.10.2 and an alternate address of 172.16.10.2. Device C is assigned a real address “172.16.10.3” and an alternate address “192.168.10.3”, and gateway GX is assigned a real address “192.168.10.100”. , gateway GY is assigned a real address "172.16.10.100".

[gateway]
According to the present invention, in order to realize UDP communication between devices connected to different subnets, such inter-subnet communication is transferred from a source subnet to a destination subnet. In each subnet, an alternative address included in the address range of the subnet is used instead of the real address of the destination device so that the address of the destination device in a different subnet can be specified. .
In the present invention, a gateway is arranged for each subnet, and each gateway executes the above-described inter-subnet communication transfer and address conversion between the real address and the alternative address.

Specifically, as shown in FIG. 1, gateways GX and GY are arranged in subnets X and Y, respectively. , Y to transfer inter-subnet communications. For this inter-gateway communication, for example, a protocol such as WebSocket capable of TCP-based two-way communication may be used. By including identification information for identifying unicast or broadcast in addition to the source, destination, and service in the data portion of the WebSocket, it is possible to define communication processing at the transfer destination gateway.

In the example of FIG. 1, the real addresses of devices A, B, and C are "192.168.10.1", "192.168.10.2", and "172.16.10.3", and the alternative addresses "172.16.10.1" and "172.16.10.1" ” and “192.168.10.3” are set. As a result, for example, when Device A on Subnet X specifies Device C on Subnet Y as the destination, the address range of Subnet X "192.168.*.*" is included in the alternative address of Device C "192.168.10.3". can be used. As a result, all devices constituting the monitoring system 1 are completely within the same subnet on the IP address.

FIG. 2 is a block diagram showing the configuration of the gateway. As shown in FIG. 2, the gateway 50 (GX, GY) includes, as main circuit configurations, a first communication interface (hereinafter referred to as first communication I/F) 51, a second communication interface (hereinafter referred to as second 2 communication I/F) 52 , a storage circuit 53 , and a control circuit 54 .

[First communication I/F]
The first communication I/F 51 is configured to perform data communication with each device connected to its own subnet.
[Second communication I/F]
The second communication I/F 52 is configured to perform inter-subnet communication using WebSocket, for example, with gateways of other subnets.

[Memory circuit]
The storage circuit 53 is composed of a semiconductor memory as a whole, and is configured to store various processing data and programs 53P used for communication control in the control circuit 54 .
The program 53P is a program that realizes various processing units that perform communication control in the control circuit 54 by cooperating with the CPU of the control circuit 54 .

[Address conversion table]
Main processing data stored in the storage circuit 53 is an address translation table UTT (Unicast Translation Table) 53A. In the UTT, for each device constituting the monitoring system 1, an address used in the subnet to which each device is connected is registered. The control circuit 54 refers to this UTT to perform address conversion between the real address and the alternate address of the device.

FIG. 3 is a configuration example of the address conversion table of the gateway. FIG. 3 shows the UTT that the gateway GX of the subnet X has. Here, for each of the devices A, B, and C that make up the monitoring system 1, an address to be used in subnet X, an address to be used in subnet Y, and replacement target information indicating whether or not to be replaced are registered. there is

In the example of FIG. 3, for device A, "192.168.10.1" is registered as an address used in subnet X, ie, a real address, and "172.16.10.1" is registered as an address used in subnet Y, ie, an alternative address. Also, "-" indicating that subnet X is not a substitute target is registered as the substitute target information. For device C, the address used in subnet X, that is, the alternate address, "192.168.10.3" is registered, and the address used in subnet Y, that is, the real address "172.16.10.3" is registered. Also, "o" indicating that the substituting target is the subnet X is registered as the substituting target information.

FIG. 4 is another configuration example of the address conversion table of the gateway. FIG. 4 shows UTTs owned by gateway GY of subnet Y. FIG. Here, for each of the devices A, B, and C that make up the monitoring system 1, an address to be used in subnet Y, an address to be used in subnet X, and substitution target information indicating whether or not the device is to be substituted are registered. there is

In the example of FIG. 4, for device A, the address used in subnet X, that is, the real address, "192.168.10.1" is registered, and the address used in subnet Y, that is, the alternate address "172.16.10.1" is registered. Also, as the substitution target information, "o" indicating that the subnet X is a substitution target is registered. For device C, the address used in subnet X, that is, the alternate address, "192.168.10.3" is registered, and the address used in subnet Y, that is, the real address "172.16.10.3" is registered. Also, "-" indicating that subnet X is not a substitute target is registered as the substitute target information.

In the UTT configuration examples shown in FIGS. 3 and 4, there are only two subnets, subnets X and Y, to which the devices of the monitoring system 1 are connected. For the destination device marked with "O", a subnet other than its own subnet can be specified as the subnet of the destination device. However, if the devices of the monitoring system 1 are distributed and connected to three or more subnets, the subnet of the destination device cannot be specified. In such a case, the UTT may have a column for registering subnets to which each device is connected. This makes it easy to identify the subnet of the destination device.

[Control circuit]
The control circuit 54 has a CPU and its peripheral circuits, and is configured to implement a processing unit that performs communication control in the control circuit 54 by causing the program 53P of the storage circuit 53 and the CPU to cooperate. .
Main processing units implemented by the control circuit 54 include a communication request transfer unit 54A and a communication request transmission unit 54B.

[Communication request transfer unit]
When communication request transfer unit 54A receives a first communication request destined for a device connected to another subnet via first communication I/F 51 from a device connected to its own subnet , generates an inter-gateway communication request including the content of the first communication request, and transfers it to the gateway of the destination subnet to which the destination device is connected via the second communication I/F 52. It is

[Communication request transmitter]
When the communication request transmitting unit 54B receives an inter-gateway communication request from another gateway connected to another subnet via the second communication I/F 52, the communication request transmitting unit 54B transmits the source address included in the inter-gateway communication request. And the destination address is referred to the UTT of the storage circuit 53 to generate a second communication request converted into an address used in its own subnet, and transmitted to its own subnet via the first communication I/F 51 is configured to

At this time, if the communication form specified in the inter-gateway communication request is unicast, the communication request transmitting unit 54B stores the transmission source address and the transmission destination address included in the inter-gateway communication request in the UTT of the storage circuit 53. It is configured to refer to and convert to an address used in its own subnet to generate a new source address and destination address. In addition, the communication request transmitting unit 54B generates a second communication request having these new source and destination addresses, and transmits the device having the new destination address via the first communication I/F 51. configured to unicast to

On the other hand, if broadcasting is not permitted in its own subnet and the communication mode specified in the inter-gateway communication request is broadcasting, the communication request transmitting unit 54B sends the source address included in the inter-gateway communication request to The UTT in the storage circuit 53 is referred to and converted into an address used in its own subnet to generate a new source address. Further, the communication request transmitting unit 54B has a new transmission source address and a new transmission destination address consisting of the address used by the device in its own subnet for each device connected to its own subnet. 2 communication request and unicast to the device via the first communication I/F 51 .

Further, when broadcasting is permitted in its own subnet and the communication mode specified in the inter-gateway communication request is broadcast, the communication request transmitting unit 54B stores the source address included in the inter-gateway communication request. Refers to the UTT of the circuit 53, converts it to an address used in its own subnet, generates a second communication request having a new source address, and sends it to its own subnet via the first communication I/F 51. Configured to send by broadcast.

[Operation of this embodiment]
Next, the operation of the monitoring system 1 according to this embodiment will be described. A case where the communication request transmitted from the source device is unicast (one-to-one communication) and a case where it is broadcast (multicast) will be described below.

[Unicast]
First, with reference to FIG. 5, the case where the first communication request transmitted from the source device is unicast will be described. FIG. 5 is a sequence diagram showing the operation (unicast) of the monitoring system. Here, a case where device A in subnet X transmits a first unicast communication request to device C in subnet Y will be described as an example.

As shown in FIG. 5, first, when device A wants to transmit data to device C, it generates a unicast communication request (first communication request) and transmits it to gateway GX (step S100). This unicast communication request includes a source address of device A's address "192.168.10.1" and a destination address of device C's address "192.168.10.3". Since subnet X uses the address for subnet X, the address of device C uses the alternate address "192.168.10.3" instead of "172.16.10.3". In the case of UDP, data to be transmitted is included in the unicast communication request.

When the gateway GX receives the unicast communication request from the device A via the first communication I/F 51, the communication request transfer unit 54A refers to the UTT in the storage circuit 53, thereby responding to the unicast communication request. Based on the included destination address "192.168.10.3", device C is specified as a destination device to be replaced, and subnet Y to which device C is connected is selected as a destination subnet (step S101).
After that, the gateway GX uses the communication request transfer unit 54A to transfer communication mode information indicating the contents of the unicast communication request, that is, the source address "192.168.10.3", the destination address "192.168.10.3", and "unicast". is generated, and transferred to the gateway GY of the subnet Y via the second communication I/F 52 (step S102).

When the gateway GY receives the inter-gateway communication request from the gateway GX via the second communication I/F 52, the communication request transmission unit 54B confirms the communication mode information included in the inter-gateway communication request, and specifies Since the received communication mode is "unicast", the source address "192.168.10.1" and the destination address "192.168.10.3" included in the inter-gateway communication request are converted to addresses used in its own subnet Y. Then, a new source address "172.16.10.1" and a new destination address "172.16.10.3" are generated (step S103).

After that, gateway GY generates a second communication request having these new source and destination addresses by means of communication request transmitting section 54B, and sends device C having the new destination address "172.16.10.3". unicast to (step S104).
As a result, device C receives the unicast communication request from device A transferred by gateways GX and GY. In the case of UDP, since data is included in the communication request, device C can obtain the data from device A included in the unicast communication request.

On the other hand, when device C wants to transmit data to device A, for example, an acknowledgment (Ack) for received data, it generates a unicast communication request (first communication request) and transmits it to gateway GY (step S110). This unicast communication request includes a source address of device C address "172.16.10.3" and a destination address of device A address "172.16.10.1". Since the address for subnet Y is used in subnet Y, the address of device A is the alternate address "172.16.10.1" instead of "192.168.10.1". In the case of UDP, data to be transmitted is included in the unicast communication request.

When the gateway GY receives the unicast communication request from the device C via the first communication I/F 51, the communication request transfer unit 54A refers to the UTT of the storage circuit 53, thereby responding to the unicast communication request. Based on the included destination address "172.16.10.1", the device A is specified as the destination device, and the subnet X to which the device A is connected is selected as the transfer destination subnet (step S111).
Thereafter, gateway GY indicates the content of the unicast communication request, that is, the source address "172.16.10.3", the destination address "172.16.10.1", and "unicast" by the communication request transfer unit 54A. A gateway-to-gateway communication request including communication mode information is generated and transferred to the gateway GX of the subnet X via the second communication I/F 52 (step S112).

When the gateway GX receives the inter-gateway communication request from the gateway GY via the second communication I/F 52, the communication request transmission unit 54B confirms the communication mode information included in the inter-gateway communication request, and specifies Since the received communication mode is "unicast", the UTT of the storage circuit 53 is referred to for the source address "172.16.10.3" and the destination address "172.16.10.1" included in the inter-gateway communication request. As a result, the address is converted into the address used in its own subnet X to generate a new source address "192.168.10.3" and a new destination address "192.168.10.1" (step S113).

Thereafter, the gateway GX generates a second communication request having these new source and destination addresses by means of the communication request transmitting unit 54B, unicast to (step S114).
As a result, device A receives the unicast communication request from device C transferred by gateways GY and GX. In the case of UDP, since data is included in the communication request, device A can obtain data from device C included in the unicast communication request, such as an acknowledgment (Ack).

[broadcast]
Next, with reference to FIG. 6, the case where the first communication request transmitted from the source device is broadcast will be described. FIG. 6 is a sequence diagram showing the operation (broadcast) of the monitoring system. Here, a case where device A on subnet X transmits a first broadcast communication request will be described as an example. It is assumed that subnet X is permitted to broadcast, and subnet Y is not permitted to broadcast.

As shown in FIG. 6, first, when device A wants to transmit data to devices B and C by broadcasting, it generates a broadcast communication request (first communication request) and transmits it to subnet X (step S200). . This broadcast communication request includes a source address of device A "192.168.10.1" and a destination address of address "192.168.255.255" indicating broadcast on subnet X. FIG. In the case of UDP, data to be transmitted is included in the unicast communication request.

When the gateway GX receives the broadcast communication request from the device A via the first communication I/F 51, the communication request transfer unit 54A refers to the UTT in the storage circuit 53 so that the request is included in the broadcast communication request. Based on the destination address "192.168.255.255", the device C is specified as the destination device to be replaced, and the subnet Y to which the device C is connected is selected as the destination subnet (step S201).
After that, the gateway GX uses the communication request transfer unit 54A to include the content of the broadcast communication request, that is, the source address "192.168.10.1", the destination address "192.168.255.255", and the communication mode information indicating "broadcast". An inter-gateway communication request is generated and transferred to gateway GY of subnet Y via second communication I/F 52 (step S202).

When the gateway GY receives the inter-gateway communication request from the gateway GX via the second communication I/F 52, the communication request transmission unit 54B confirms the communication mode information included in the inter-gateway communication request, and specifies Since the requested communication mode is "broadcast" and is not permitted in subnet Y, the broadcast communication request is converted to a unicast communication request as follows.
First, the gateway GY converts the transmission source address "192.168.10.1" included in the inter-gateway communication request to the address used in its own subnet Y by referring to the UTT of the storage circuit 53 using the communication request transmission unit 54B. After conversion, a new source address "172.16.10.1" is generated (step S203).

Subsequently, the gateway GY specifies the device corresponding to the destination address "192.168.255.255" included in the inter-gateway communication request by referring to the UTT of the storage circuit 53 using the communication request transmitting unit 54B. In FIG. 4, device C having an alternative address "192.168.10.3" is registered, device C is specified as a destination device, and a new destination address "172.16.10.3" is generated (step S203).

After that, gateway GY generates a second communication request having these new source and destination addresses by means of communication request transmitting section 54B, and sends device C having the new destination address "172.16.10.3". unicast to (step S204).
As a result, device C can receive the broadcast communication request from device A transferred by gateways GX and GY as a unicast communication request even if broadcasting is not permitted in subnet Y. FIG. In the case of UDP, since data is included in the communication request, device C can obtain the data from device A included in the unicast communication request.

If broadcasting is permitted on subnet Y, gateway GY causes communication request transmission unit 54B to change the destination address "192.168.255.255" included in the inter-gateway communication request to a new address indicating broadcast on subnet Y. destination address "172.16.255.255" (step S205).
Thereafter, gateway GY generates a second communication request having these new source and destination addresses by means of communication request transmitter 54B, and broadcasts it to subnet Y (step S206).

[Effects of this embodiment]
Thus, in this embodiment, the gateways GX and GY are provided for each of the subnets X and Y to which the devices A, B and C of the monitoring system 1 are connected. When a first communication request addressed to a device connected to another subnet is received from a connected device, an inter-gateway communication request including the content of the first communication request is generated and sent. When forwarding to the gateway of the destination subnet to which the destination device is connected and receiving an inter-gateway communication request from another gateway, the source address and destination address included in the inter-gateway communication request are transferred to the own subnet. It is configured to generate a second communication request converted to the address to be used and transmit it to its own subnet.

At this time, each device has an address used in its own subnet and an address used in the destination subnet. Therefore, all the devices of the monitoring system 1 are contained within one subnet when viewed from IP addresses. This allows devices to be extended and connected to other subnets, and enables flexible support for the configuration of the underlying communication network. Therefore, even when mixed with another system on a new communication network, or when connecting a cloud service that does not support broadcasting such as AWS (Amazon Web Services) and an on-premises system, Existing surveillance systems can be applied without requiring major modifications.

Moreover, it is not necessary to install an address management server in addition to the packet conversion device, and it is possible to cope with this by simply installing a gateway for each subnet. As a result, an increase in equipment cost can be suppressed, and it is possible to deal with the problem at low cost.
Also, the communication mode of the destination subnet need not be limited to multicast, and the communication mode of the destination subnet may be unicast or broadcast. This allows flexible mixing of destination subnets with other systems.

[Expansion of Embodiment]
Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a non-contradictory range.

1... Monitoring system, 10, 20, 30, X, Y, Z... Subnet, 11, 12, 22, A, B, C... Device, 13, 21, GX, GY, 50... Gateway, 51... First Communication I/F 52 Second communication I/F 53 Storage circuit 53A Address conversion table (UTT) 53P Program 54 Control circuit 54A Communication request transfer unit 54B Communication request transmission Part, R: Relay system.

Claims (8)

multiple devices connected to one of multiple subnets; and
and a plurality of gateways connected to each of the plurality of subnets,
each of the plurality of devices has an address used in its own subnet and an address used in another subnet;
each of the plurality of gateways,
a first communication interface configured to perform data communication with a device connected to its own subnet among the plurality of devices, and a gateway connected to another subnet among the plurality of gateways; a second communication interface configured to communicate data between
When receiving a first communication request destined for a device connected to another subnet from a device connected to its own subnet, it generates an inter-gateway communication request including the contents of the first communication request. is transferred to the gateway of the destination subnet to which the destination device is connected, and when the inter-gateway communication request is received from another gateway, the source address and destination address included in the inter-gateway communication request is converted into an address used in its own subnet to generate a second communication request and transmit the second communication request to its own subnet. The monitoring system of claim 1, wherein
each of the plurality of gateways,
a storage circuit configured to store, for each of the plurality of devices, an address conversion table in which an address used in the device's own subnet and an address used in another subnet are registered;
When receiving the inter-gateway communication request, referring to the address conversion table, the source address and the destination address included in the inter-gateway communication request are converted into addresses used in its own subnet. A surveillance system characterized by: The monitoring system of claim 1, wherein
The inter-gateway communication request is characterized by including a source address and a destination address included in the first communication request, and communication mode information indicating the communication mode specified in the first communication request. Monitoring system. In the monitoring system of claim 3,
When the communication mode specified in the inter-gateway communication request is unicast, each of the plurality of gateways converts the source address and the destination address included in the inter-gateway communication request to addresses used in its own subnet. generating a new source address and destination address by conversion, and transmitting the second communication request having these new source address and destination address by unicast to the device having the new destination address; A surveillance system, characterized in that it is configured to: In the monitoring system of claim 3,
When each of the plurality of gateways is not permitted to broadcast in its own subnet and the communication mode specified in the inter-gateway communication request is broadcast, each of the plurality of gateways sets the source address included in the inter-gateway communication request to itself. generated a new source address by converting it to the address used in the subnet of the self, and consists of the new source address and the address used in the self subnet of the device for each device connected to its own subnet A monitoring system, wherein the second communication request having a new destination address is generated and transmitted to the device by unicast. In the monitoring system of claim 3,
Each of the plurality of gateways is permitted to broadcast in its own subnet, and if the communication mode specified in the inter-gateway communication request is broadcasting, each of the plurality of gateways uses the transmission source address included in the inter-gateway communication request as its own subnet. The monitoring system is configured to generate the second communication request having a new transmission source address converted to an address used in the subnet, and to transmit the second communication request to its own subnet by broadcast. a plurality of devices connected to one of a plurality of subnets, and a plurality of gateways connected to each of the plurality of subnets, each of the plurality of devices having an address used in its own subnet and the gateway used in a surveillance system, having an address used in a subnet,
a first communication interface configured to perform data communication with a device connected to its own subnet among the plurality of devices;
a second communication interface configured to perform data communication with a gateway connected to another subnet among the plurality of gateways;
When receiving a first communication request destined for a device connected to another subnet from a device connected to its own subnet, it generates an inter-gateway communication request including the contents of the first communication request. is transferred to the gateway of the destination subnet to which the destination device is connected, and when the inter-gateway communication request is received from another gateway, the source address and destination address included in the inter-gateway communication request a second communication request converted to an address used in its own subnet, and a control circuit configured to transmit it to its own subnet. 8. The gateway of claim 7, wherein
a storage circuit configured to store, for each of the plurality of devices, an address conversion table in which an address used in the device's own subnet and an address used in another subnet are registered;
When the control circuit receives the inter-gateway communication request, the control circuit refers to the address conversion table and converts the source address and the destination address included in the inter-gateway communication request into addresses used in its own subnet. A gateway, characterized in that it is configured to:

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