Method, communication system and coupled communication device for transmitting time-critical data

Abstract

The invention relates to a method for transmitting time-critical data, wherein a datagram (100) is sent from a first communication device (103, 105) in a first subnet (1) to a second communication device (221) in a second subnet (2) via a third subnet (3). In the first subnet and the second subnet, the datagram is forwarded by switching, respectively, while the datagram in the third subnet is forwarded by routing. The first subnet comprises at least a first coupling communication device (101) connected to a first router (301) and a second coupling communication device (102) connected to a second router (302). The first and second coupling communication devices select a master coupling communication device from each other, wherein the two coupling communication devices are provided with a common virtual network layer address. A data link layer tunnel (10) is established between the master coupling communication device and the third coupling communication device (201) via the third subnet (3).

Description

Technical Field

[0001] The invention relates to a method for transmitting time-critical data, which method is particularly suitable for industrial automation systems, and to a communication system and a coupled communication device for carrying out the method. Background Art

[0002] Industrial automation systems usually include a number of automation devices that are networked to each other via an industrial communication network and are used to control or regulate facilities, machines or equipment within the scope of manufacturing automation or process automation. Due to the time-critical framework conditions of industrial automation systems, communication between automation devices mainly uses real-time communication protocols such as PROFINET, PROFIBUS, Real-Time Ethernet or Time-Sensitive Networking (TSN). In particular, control services and applications can be automatically and workload-dependently distributed to currently available servers or virtual machines in the industrial automation system.

[0003] Interruptions in the communication link between computer units or automation devices of an industrial automation system can lead to undesired or unnecessary duplication of the transmission of service requests. In addition, untransmitted or incompletely transmitted information can prevent the industrial automation system from transitioning to or remaining in a safe operating state.

[0004] In Ethernet-based communication networks, problems arise if network resources used to transmit real-time data streams or data frames are competitively claimed for the transmission of data frames with large user data content but without special quality of service requirements. This ultimately results in the data streams or data frames with real-time requirements not being transmitted with the requested or required quality of service.

[0005] The Common Address Redundancy Protocol (CARP) enables application servers, firewalls or routers to be implemented as high-availability systems. For this purpose, at least two redundant system components are provided, which can assume the same tasks and are assigned to the same subnet. The redundant system components each have a unique IP and MAC address and form a device complex. The device complex is also equipped with an IP and MAC address, via which other devices or systems communicate with the device complex. The system components in the device complex assume the master role for completing the tasks of the device complex, while the other system components assume the slave role. If the system component with the master role fails, the system component currently assigned to the slave role will take over its tasks and can be connected via the IP or MAC address assigned to the device complex.

[0006] While the failure of a section in a route can be easily compensated by dynamic routing or the selection of an alternative section, the failure of the default gateway configured in the terminal device is more problematic. If the default gateway is not available as the first router for the terminal device, routing from the affected subnet is in principle not possible. Using the Hot Standby Router Protocol (HSRP), multiple routers can be combined into a device group and implemented as a logical router via this device group. This logical router is equipped with an IP and MAC address via which the master router of the selected device group can be reached. All other routers represent secondary routers and are temporarily unreachable via the IP or MAC address assigned to the logical router. The primary router signals its functional readiness to the secondary routers via multicast messages that are sent as a standard every 3 seconds. If these multicast messages are not received for a longer period of time, e.g. 10 seconds, the current secondary router is selected as the new master router and the IP or MAC address assigned to the logical router is bound to its network interface.

[0007] The Virtual Router Redundancy Protocol (VRRP) can also solve the problem of default gateway or terminal device first router failure. Unlike HSRP, VRRP allows the IP address of the physical router to be used as the IP address of the logical router implemented by the device group.

[0008] EP 3 646 559 B1 relates to a method for checking datagrams transmitted in an industrial automation system having a plurality of automation units, wherein the datagrams to be checked are transmitted from the automation units via respective firewall interfaces for checking to a firewall system and checked there according to rules. The firewall system is formed by at least one virtual machine provided in a data processing system, the data processing system comprising a plurality of computer units. In order to transmit the datagrams to be checked, data link layer tunnels are respectively established between the respective firewall interfaces and the firewall system. The datagrams to be checked and at least the datagrams which have been successfully checked are both transmitted in the respective data link layer tunnels.

[0009] EP 3 035 606 A1 describes a method for data transmission in a communication network comprising at least two virtual local area networks, wherein data streams are respectively assigned data stream individual target device identifiers. When a data stream is transmitted from a source communication device assigned to a first virtual local area network to a target communication device assigned to a second local area network, the identifier assigned to the data stream in the first virtual local area network is converted into an identifier assigned to the data stream in the second virtual local area network.

[0010] A method for transmitting time-critical data is known from the prior international patent application WO 2021 / 239371Al, in which a datagram is sent from a first communication device in a first subnet to a second communication device in a second subnet via a third subnet. The first subnet and the third subnet are connected via a first switch, and the second subnet and the third subnet are connected via a second switch. The datagram is forwarded from the first communication device to the first switch via an identifier and a priority specification of the first virtual local area network. The first switch encapsulates the datagram sent by the first communication device in a data frame assigned to the data stream via the third subnet, and inserts an identifier of the second virtual local area network into the data frame.

[0011] According to the above-mentioned prior international patent application WO 2021 / 239371 Al, resources are reserved along the selected path in the third subnet through the second virtual local area network identifier. The second switch extracts the datagram encapsulated in the data frame assigned to the data flow from the received data frame, and forwards the extracted datagram to the second communication device through the first virtual local area identifier and the priority description.

[0012] US2020 / 084144 Al describes a method in which network traffic is received on a redundant gateway device, which is set up according to a redundant gateway protocol. Known unicast traffic received on the redundant gateway device is forwarded from the redundant gateway device to a tunnel endpoint via a tunnel established according to a tunnel protocol. If the redundant gateway device is a primary gateway according to the redundant gateway protocol, broadcast traffic, unknown unicast traffic, and multicast traffic will be forwarded to the tunnel endpoint via the tunnel. If the redundant gateway device is a backup gateway according to the redundant gateway protocol, broadcast traffic, unknown unicast traffic, and multicast traffic will be discarded.

[0013] EP 3 787 237 A1 discloses a method for data transmission in a redundantly operable communication network, the network comprising at least a first subnetwork and a second subnetwork, the two subnetworks each comprising communication devices connected to one another in a ring topology. Communication devices with activated ring control units are provided in each of the two subnetworks. The two subnetworks are connected to one another via two coupling links, the two coupling links respectively connecting two coupled communication devices. Before a fault occurs, the coupling link to which the selected coupled communication device is connected operates as an inactivated standby coupling link, while the other coupling link operates as an activated main coupling link. The coupled communication device connected to the main coupling link transmits a status datagram to the selected coupled communication device, the status datagram also additionally comprising configuration information on whether each coupled communication device connected to the main coupling link comprises an activatable ring control unit.

[0014] When transparently transmitting datagrams between data link layer subnets, in which datagrams are forwarded by switching means according to OSI layer 2, and network layer or switching layer subnets, in which datagrams are forwarded by routing means according to OSI layer 3, it is not only important that the original information is transmitted without falsification. Even more important is the requirement that the data transmission via the network tunnel is robust against failures of system components when using tunneling protocols.

[0015] In principle, mutually redundant tunnel endpoints can be implemented via Ethernet VPN (EVPN) according to IETF RFC8365 (see https: / / datatracker.ietf.org / doc / htmf / rfc8365). However, this concept requires a huge effort to implement, especially in public 5G mobile networks, or is too complex for use in simpler automation networks. Summary of the invention

[0016] The object of the present invention is to create a method for transparently transmitting time-critical data via a network layer switching network that is implementable with little effort, which method can compensate for failures of system components, and to provide suitable embodiments for carrying out the method.

[0017] This object is achieved by a method according to the invention having the features of the invention, a communication system having the features of the invention and by a coupled communication device having the features of the invention. Advantageous developments of the invention are given in the dependent claims.

[0018] According to the method for transmitting time-critical data of the present invention, a datagram is sent from a first communication device in a first subnet to a second communication device in a second subnet via a third subnet. The first and third subnets are connected via at least a first and a second router, and the second and third subnets are connected via at least a third router. In the first and second subnets, the datagram is forwarded via a switching mode, respectively. In contrast, the datagram in the third subnet is forwarded via a routing mode.

[0019] Furthermore, according to the present invention, the first subnet has a ring topology and comprises at least a first coupling communication device connected to the first router and a second coupling communication device connected to the second router. The second subnet comprises a third coupling communication device, which is connected to the third router and is provided with a network layer address. Furthermore, the first and second coupling communication devices select a master coupling communication device between each other. The two coupling communication devices or the master coupling communication device are provided with a common virtual network layer address. The first or second coupling communication device which is not selected as the master communication device operates as a reserve coupling communication device. The coupling communication device is in particular a switch.

[0020] According to the invention, the first and second coupled communication devices select a master coupled communication device from each other via a virtual router redundancy protocol (VRRP). Advantageously, the virtual network layer addresses of the first and second coupled communication devices can also be provided via VRRP. In order to use the data link layer tunnel, information about the virtual network layer addresses of the first coupled communication device and the second coupled communication device is propagated in the first subnet by means of VRRP announcements.

[0021] According to the present invention, at least between the main coupling communication device and the third coupling communication device, a data link layer tunnel is established through the third subnet via the first or second router and the third router. The datagram sent from the first communication device to the second communication device is encapsulated in a tunnel data frame within the data link layer tunnel, in particular, by inserting the datagram into the payload data field of the tunnel data frame. The first endpoint of the data link layer tunnel is configured with the virtual network layer addresses of the first and second coupling communication devices. In contrast, the second endpoint of the data link layer tunnel is configured with the network layer address of the third coupling communication device. The tunnel data frame is a second layer tunnel frame of a VXLAN frame or a datagram, and the datagram sent from the first communication device to the second communication device is respectively encapsulated in the tunnel data frame.

[0022] According to the invention, the first subnetwork has a ring topology and datagrams in the first subnetwork are transmitted according to the Media Redundancy Protocol (MRP). When the selection of the primary coupled communication device changes or the primary coupled communication device fails, an MRP-Interconnection- ) signal. By sending the MRP interconnection topology change signal, a relearning of the data link layer address table of each communication device is triggered in all communication devices (which can be switches or bridges in particular) of the first subnet. In this way, the communication devices in the first subnet can quickly and reliably adjust their configuration to the change in the selection of the coupled communication device that operates as the master coupled communication device.

[0023] The invention thus enables a simple, automatic configuration of mutually redundant tunnel end points and an automatic reconfiguration of the communication devices affected thereby in the first subnet. In this way, time-critical data can be transmitted redundantly and transparently via the network layer switching network without interruptions of the data link layer tunnel due to the failure of a single tunnel end point. By using VRRP to select the master coupling communication device and to provide virtual network layer addresses for the first and second coupling communication devices or for the master coupling communication device, a reliable and low-cost implementation can be achieved. Furthermore, with the invention, in principle any number of mutually redundant tunnel end points can be used. The selection of the master coupling communication device and the provision of the virtual network layer addresses are not limited to two coupling communication devices, but can be easily extended to a larger number of mutually redundant coupling communication devices.

[0024] According to a particularly preferred embodiment of the present invention, at least the first and second coupling communication devices form a coupling communication device group, which is assigned to a virtual data link layer tunnel endpoint. To this end, the coupling communication devices from the same group assigned to the virtual data link layer tunnel endpoint share information about the respective operating states of the coupling communication devices with one another and use this information to monitor the master coupling communication device for failures. When a previously activated master coupling communication device fails, all reserve coupling communication devices select a new master coupling communication device from one another.

[0025] For example, the first communication device can insert a virtual local area network identifier and a priority specification in a datagram sent to the second communication device. Advantageously, the datagram is forwarded from the first communication device to the primary coupling communication device using the identifier of the first virtual local area network and the priority specification. The primary coupling communication device then encapsulates the datagram sent by the first communication device in a tunnel data frame. In contrast, the third coupling communication device extracts the datagram encapsulated in the tunnel data frame from the received tunnel data frame and forwards the extracted datagram to the second communication device using the virtual local area network identifier and the priority specification. In this way, the virtual local area network identifier and the priority specification used for transmitting datagrams, in particular datagrams in an OSI layer 2 network, can also be used transparently in a superimposed OSI layer 3 transit network.

[0026] The first and second subnets can be assigned to the PROFINET unit, while the third subnet can be an IP-based transit network. The datagrams are PROFINET frames. Since the above-described method for configuring a tunnel endpoint can also be easily implemented in a tunnel endpoint of a mobile radio network, the second subnet can include a mobile radio network, in particular a 5G mobile radio network, while the third subnet is an IP-based transit network.

[0027] Preferably, an MRP interconnection topology change signal is sent through an MRP_InTopologyChange frame, and the data link layer address table is respectively designed as a forwarding database. In this case, by sending the MRP interconnection topology change signal, relearning of the respective forwarding databases of the communication devices is triggered in all communication devices of the first subnet. According to another advantageous embodiment of the present invention, by sending the MRP interconnection topology change signal, relearning of at least one data link layer address assigned to the first endpoint of the data link layer tunnel is triggered in the routers along the data link layer tunnel.

[0028] The communication system according to the present invention is used to perform the method described above and has a first subnet, which includes at least a first communication device, a first coupled communication device and a second coupled communication device. In addition, the communication system also has a second subnet, which includes at least a second communication device and a third coupled communication device. In addition, a third subnet is provided, which includes at least a first router, a second router and a third router. The first and third subnets are connected via at least a first and a second router, and the second and third subnets are connected via at least a third router.

[0029] The communication devices and coupled communication devices of the communication system according to the invention are designed to forward datagrams in the first and second subnetworks by switching. In contrast, the router of the communication system according to the invention is designed to forward datagrams in the third subnetwork by routing. Furthermore, the first subnetwork of the communication system according to the invention has a ring topology, and the first coupled communication device is connected to the first router, while the second coupled communication device is connected to the second router. Furthermore, the third coupled communication device is connected to the third router, and the former also has an assigned network layer address. The first subnetwork is designed to transmit datagrams in the first subnetwork according to the media redundancy protocol (MRP).

[0030] The first and second coupled communication devices of the communication system according to the present invention are designed to select a master coupled communication device from each other through a virtual router redundancy protocol (VRRP) and to be provided with a common virtual network layer address. In addition, the first and second coupled communication devices are designed to operate the first or second coupled communication device that has not been selected as the master communication device as a reserve coupled communication device. In addition, the first and second coupled communication devices of the communication system according to the present invention are designed to send a signal of a change in the MRP interconnection topology when the selection of the master coupled communication device changes or the master coupled communication device fails, and by sending the signal of the change in the MRP interconnection topology, relearning of the data link layer address table of each communication device is triggered in the communication devices of the first subnet.

[0031] The coupling communication device of the communication system according to the present invention is designed to establish a data link layer tunnel between the main coupling communication device and the third coupling communication device through the first or second router and the third router through the third subnet, and the datagram sent from the first communication device to the second communication device is encapsulated in a tunnel data frame in the data link layer tunnel. The tunnel data frames that respectively encapsulate the datagram sent from the first communication device to the second communication device are VXLAN frames or second layer tunnel frames of datagrams. In addition, the coupling communication device is designed to configure the first endpoint of the data link layer tunnel with the virtual network layer addresses of the first and second coupling communication devices. In addition, the coupling communication device is designed to configure the second endpoint of the data link layer tunnel with the network layer address of the third coupling communication device.

[0032] The coupling communication device according to the invention is used to carry out the method according to the above description and is designed similarly to the coupling communication device of the communication system according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is explained in more detail below with reference to exemplary embodiments. The accompanying drawings show:

[0034] Figure 1 A communication system comprising a plurality of subnets is shown for transmitting time-critical data having a plurality of data link layer tunnels,

[0035] Figure 2 Shows the basis for switching the data link layer tunnel endpoint Figure 1 The communication system shown,

[0036] Figure 3 Show according to Figure 1 Schematic diagram of datagrams exchanged between communication devices of different subnets in the communication system shown, before being encapsulated into tunnel data frames,

[0037] Figure 4 A schematic diagram showing a tunnel data frame, according to Figure 3 The datagram shown is encapsulated in the data frame. DETAILED DESCRIPTION

[0038] Figure 1The communication system for an industrial automation system shown is divided into four subnets 1-4. In the first subnet 1 and the second subnet 2, datagrams 100 are forwarded by means of switching. To this end, the first subnet 1 and the second subnet 2 respectively include a plurality of bridges or switches 101-102, 104, 201-204 as communication devices for forwarding datagrams, and automation devices 103, 105 with bridge or switch functions, such as programmable logic controllers. The switches 101-102, 104, 201-204 respectively include a plurality of ports and are particularly used to connect programmable logic controllers 103, 105, 221, operating and observation stations, I / O controllers or I / O modules that also constitute communication devices or communication terminals.

[0039] The programmable logic controller 103, 105, 221 usually includes a communication module, a central processing unit and at least one input / output unit. In principle, the input / output unit can also be designed as a distributed peripheral module, which is arranged at a certain distance from the programmable logic controller. The programmable logic controller 103, 105, 221 can be connected to a switch or a router via a communication module or additionally connected to a field bus. The input / output unit is used to exchange control variables and measured variables between the programmable logic controller 103, 105, 221 and the machine or device 131, 151, 222 controlled by the respective programmable logic controller 103, 105, 221. The central processing unit is particularly used to determine suitable control variables from the recorded measured variables. The components of the above-mentioned programmable logic controller 103, 105, 221 are interconnected, for example, via a backplane bus system.

[0040] In order to exchange control variables and measured variables with the connected machines or devices, I / O modules can also be provided in principle. The I / O modules can be controlled in particular by an I / O controller per automation unit. For this purpose, the I / O modules can also be driven by a remote programmable logic controller as an alternative.

[0041] The datagram 100 is forwarded in the third subnet 3 by means of routing. In this embodiment, the third subnet is an IP-based overlapping transit network. To this end, the third subnet 3 includes a plurality of routers 301-304. The first subnet 1 and the third subnet 3 are connected via at least the first router 301 and the second router 302, while the second subnet 2 and the third subnet 3 are connected via at least the third router 303.

[0042] In order to couple the first subnet 1 with the third subnet 3, the first subnet 1 includes at least a first coupling communication device 101 connected to the first router 301 and a second coupling communication device 102 connected to the second router 302. Here, the two coupling communication devices 101-102 are redundant with each other. In the present embodiment, on the other hand, the second subnet 2 only includes a coupling communication device 201 connected to the third router 303 and constitutes a Figure 1 A third coupled communication device of the communication system is shown.

[0043] In the present embodiment, the first subnet 1 and the second subnet 2 both have a ring topology, thus providing a basis for applying a ring redundancy protocol, such as a media redundancy protocol (MRP) for the first subnet 1 or the second subnet 2 or a high availability seamless redundancy protocol (HSR) for the second subnet 2. Preferably, the datagram 100 is transmitted in the first subnet 1 and the second subnet 2 accordingly. The first subnet 1 and the second subnet 2 can be assigned to a PROFINET unit in particular. In this case, the datagram 100 is a PROFINET frame.

[0044] In principle, the second subnetwork 2 can also have a tree topology, thereby providing a basis for applying a spanning tree protocol, such as the spanning tree protocol (STP), the multiple spanning tree protocol (MSTP) or the rapid spanning tree protocol (RSTP). Such spanning tree protocols also provide redundancy functions, making it possible to compensate for failures of individual transmission sections or links.

[0045] Furthermore, the communication system comprises a fourth subnetwork 4, which is coupled to the third subnetwork 3 in a similar manner to the second subnetwork 2 and comprises a mobile radio network, in particular a 5G mobile radio network, with a plurality of base stations 401-404. In this case, the fourth subnetwork 4 and the third subnetwork 3 are connected at least via a fourth router 304. A mobile radio modem 405, to which an automation device 451, such as an operating and observation station, is connected, for example, can be connected to these base stations 401-404. In this case, the mobile radio modem 405 forms a fourth coupling communication device for connecting the operating and observation station 451 to the overlapping third subnetwork 3.

[0046] The operating and viewing station 451 is used to visualize process data or measured variables and control variables processed or recorded by a programmable logic controller, an input / output unit or a sensor. The operating and viewing station 451 is used in particular to display the values ​​of control circuits and to change control parameters. The operating and viewing station 451 comprises at least a graphical user interface, an input device, a processor unit and a communication module.

[0047] In the communication system, datagrams 100 are exchanged, i.e., bidirectionally sent and received, between a first communication device in the first subnet 1 and a second communication device in the second subnet 2, in particular via the overlapping third subnet 3. Here, for example, the programmable logic controllers 103, 105 in the first subnet 1 can constitute the first communication device, while the programmable logic controller 221 in the second subnet 2 can constitute the second communication device.

[0048] The first coupling communication device 101 and the second coupling communication device 102, together with the respective other coupling communication device, are each designed to select a master coupling communication device from each other and are assigned a common virtual network layer address (address for OSI layer 3). In addition, both coupling communication devices 101, 102 are designed so that the first coupling communication device or the second coupling communication device that is not selected as the master communication device operates as a reserve coupling communication device. Figure 1 As shown, the first coupled communication device 101 is selected as the master communication device.

[0049] According to a preferred embodiment, the two mutually redundant coupled communication devices 101, 102 select the master coupled communication device from each other by means of the Virtual Router Redundancy Protocol (VRRP). Therefore, the virtual network layer addresses of the two mutually redundant coupled communication devices 101, 102 are also provided by VRRP. In addition, in order to use the data link layer tunnel 10, information about the virtual network layer addresses of the two mutually redundant coupled communication devices 101, 102 is propagated in the first subnet 1 by means of VRRP advertisements 110.

[0050] A data link layer tunnel 10 is established between the primary coupled communication device 101 or 102 and the third coupled communication device 201 via the first router 301 or via the second router 302 and via the third router 303 through the third subnet 3. In this case, the datagram 100 sent from the first communication device 103, 105 to the second communication device 221 is encapsulated in a tunnel data frame 200 within the data link layer tunnel 10. The same applies in the opposite direction.

[0051] The main coupled communication device encapsulates the datagram 100 sent from the first communication device to the second communication device by inserting the datagram into the payload data field of the tunnel data frame 200. Preferably, the tunnel data frame 200 in which the datagram 100 sent from the first communication device to the second communication device is respectively encapsulated is a VXLAN frame or a second layer tunnel frame of the datagram.

[0052] In the present embodiment, another data link layer tunnel 20 is also established between the primary coupled communication device 101 or 102 and the fourth coupled communication device 405 via the first router 301 or via the second router 302 and via the fourth router 304 through the third subnet 3. Here, the datagram 100 sent from the first communication device 103, 105 to the operation and observation station 451 is encapsulated in a tunnel data frame 200 within the other data link layer tunnel 20. Otherwise, data is transmitted via the other data link layer tunnel 20, and the other data link layer tunnel 20 is configured and set in the same way as the data link layer tunnel 10 is used. Therefore, the following explanations about the data link layer tunnel 10 also apply to the other data link layer tunnel 20 by analogy.

[0053] The two mutually redundant coupling communication devices 101, 102 are respectively designed to configure the first end point of the data link layer tunnel 10 using the virtual network layer addresses of the first coupling communication device and the second coupling communication device or the main coupling communication device, and to configure the second end point of the data link layer tunnel 10 using the network layer address of the third coupling communication device 201. Here, the first end point is assigned to the first subnet 1, and the second end point is assigned to the second subnet 2.

[0054] Mutually redundant coupled communication devices 101, 102 form a coupled communication device group that is equipped with a virtual data link layer tunnel endpoint. Coupled communication devices from the same group assigned to the virtual data link layer tunnel endpoint share information about the respective operating states of the coupled communication devices with each other and use this information to monitor their respective master coupled communication devices for faults. When a previously activated master coupled communication device fails, all reserve coupled communication devices in principle select a new master coupled communication device from among themselves. For example, if the first coupled communication device 101 fails as the activated master coupled communication device, the second coupled communication device 102 will take over as the master coupled communication device. According to Figure 2 As shown, in this case, the data link layer tunnel 10 is established via the second router 302 and the third router 303. Similarly, another data link layer tunnel 20 is established via the second router 302 and the fourth router 304.

[0055] In the present embodiment, datagrams 100 are transmitted in the first subnet 1 according to the media redundancy protocol (MRP). When the selection of the primary coupled communication device changes or a primary coupled communication device fails, an MRP interconnection topology change signal is issued. For example, the MRP interconnection topology change signal can be issued by means of an MRP_InTopologyChange frame. Advantageously, by issuing the MRP interconnection topology change signal, a relearning of the data link layer address table or forwarding database (FDB) of each communication device is triggered in the communication devices 101-105 of the first subnet 1. Preferably, when the MRP interconnection topology changes, all communication devices 101-105 of the first subnet 1 relearn the forwarding database of each communication device. In a corresponding manner, by issuing the MRP interconnection topology change signal, a relearning of the data link layer address assigned to the first end point of the data link layer tunnel 10, 20 is triggered in the routers 301-304 along the data link layer tunnel 10, 20.

[0056] In accordance with Figure 3 In the present exemplary embodiment, a first communication device, for example one of the programmable logic controllers 103, 105, inserts an identifier 12 of a first virtual local area network (VLAN), for example VID=0, and a priority specification 13, for example PCP=6, into a datagram 100, which is sent to a second communication device, for example the programmable logic controller 221. Thus, in a PROFINET unit comprising the first subnet 1 or the second subnet 2, high-priority control data that is cyclically transmitted in the PROFINET unit within a predefined or reserved time window is identified. To this end, in the present exemplary embodiment, all communication devices 101-105, 201-204, 221 are operated in a clock-synchronous manner in the PROFINET unit. Based on the identifier 12 of the first virtual local area network and the priority specification 13, the datagram is forwarded from the first communication device to the master coupling communication device. The datagram 100 includes an address field 11 and a payload data field 14, and in the present exemplary embodiment, the datagram 100 corresponds essentially to an Ethernet frame in terms of its structure.

[0057] according to Figure 4As shown, the master coupled communication device encapsulates the datagram 100 sent by the first communication device by inserting the datagram into the payload data field 24 of the tunnel data frame 200. In this case, the payload data field 24 of the tunnel data frame 200 includes in particular the identifier 12 of the first virtual local area network and the priority specification 13 for forwarding within the first subnet or the second subnet. In addition, the tunnel data frame 200 includes an address field 21 and corresponds to an Ethernet frame in terms of its structure. In addition, the identifier 22 of the second virtual local area network used for routing through the data link layer tunnel 10, for example VID'=1, and the priority specification 23, for example PCP'=6, can also be inserted in the tunnel data frame 200.

[0058] The third coupled communication device 201 extracts the datagram 100 encapsulated in the tunnel data frame 200 from the received tunnel data frame 200 and forwards the extracted datagram 100 to the second communication device based on the identifier 12 of the virtual local area network and the priority specification 13. In a corresponding manner, the fourth coupled communication device 405 extracts the datagram 100 for the operating and observing station 451 from the tunnel data frame 200 and forwards the datagram 100 to the operating and observing station 451.

Claims

1. A method for transmitting time-critical data, wherein: - sending a datagram (100) from a first communication device (103, 105) in a first subnet (1) to a second communication device (221) in a second subnet (2) via a third subnet (3), - connecting the first subnet and the third subnet via at least a first router and a second router, and connecting the second subnet and the third subnet via at least a third router, - forwarding the datagram in the first subnet and the second subnet respectively by means of switching, - forwarding the datagram within the third subnet by means of routing, the first subnetwork has a ring topology and comprises at least a first coupled communication device (101) connected to the first router and a second coupled communication device (102) connected to the second router, wherein datagrams are transmitted within the first subnetwork according to the Media Redundancy Protocol, MRP, - the second subnet comprises a third coupling communication device (201), the third coupling communication device being connected to the third router and being provided with a network layer address, - the first coupled communication device and the second coupled communication device select a master coupled communication device from among each other by means of a virtual router redundancy protocol, VRRP, wherein a common virtual network layer address is assigned to both coupled communication devices and the first coupled communication device or the second coupled communication device which has not been selected as the master communication device is operated as a reserve coupled communication device, - when the selection of the primary coupled communication device changes or the primary coupled communication device fails, sending an MRP interconnection topology change signal, - triggering relearning of the data link layer address table of each of the communication devices in the first subnet by sending an MRP interconnection topology change signal, - establishing a data link layer tunnel (10) at least between the primary coupled communication device and the third coupled communication device via the first router or the second router and via the third router through the third subnet, wherein the datagram sent from the first communication device to the second communication device is encapsulated in a tunnel data frame (200) within the data link layer tunnel, and the tunnel data frame is a VXLAN frame or a second layer tunnel frame of the datagram, and the datagram sent from the first communication device to the second communication device is respectively encapsulated in the tunnel data frame, - configuring a first endpoint of the data link layer tunnel with the virtual network layer addresses of the first coupled communication device and the second coupled communication device, - configuring a second endpoint of said data link layer tunnel with said network layer address of said third coupled communication device.

2. The method according to claim 1, wherein: The virtual network layer addresses of the first coupled communication device and the second coupled communication device are provided by means of VRRP.

3. The method according to any one of claims 1 or 2, wherein: In order to use the data link layer tunnel, information about the virtual network layer addresses of the first coupled communication device and the second coupled communication device is propagated in the first subnet by means of VRRP advertisements.

4. The method according to any one of claims 1 to 2, wherein: At least the first coupling communication device and the second coupling communication device form a coupling communication device group, which is assigned to a virtual data link layer tunnel endpoint, wherein the coupling communication devices from the same group assigned to the virtual data link layer tunnel endpoint share information about the respective operating states of the coupling communication devices with each other and monitor the main coupling communication device for failures based on the information, and wherein, when a previously activated main coupling communication device fails, all reserve coupling communication devices select a new main coupling communication device from among each other.

5. The method according to any one of claims 1 to 2, wherein: The primary coupled communication device (101, 102) encapsulates the datagram (100) transmitted from the first communication device (103, 105) to the second communication device (221) by inserting the datagram into a payload data field (24) of the tunnel data frame (200).

6. The method according to any one of claims 1 to 2, wherein: The first communication device (103, 105) inserts a virtual local area network identifier (12) and a priority specification (13) into the datagram (100) sent to the second communication device (221), wherein the datagram is forwarded from the first communication device to the primary coupling communication device based on the virtual local area network identifier and the priority specification, wherein the primary coupling communication device encapsulates the datagram sent by the first communication device in the tunnel data frame (200), and wherein the third coupling communication device extracts the datagram encapsulated in the tunnel data frame from the received tunnel data frame and forwards the extracted datagram to the second communication device based on the virtual local area network identifier and the priority specification.

7. The method according to any one of claims 1 to 2, wherein: The first subnet and the second subnet are assigned to a PROFINET unit, wherein the third subnet is an IP-based transit network, and wherein the datagrams are PROFINET frames.

8. The method according to any one of claims 1 to 2, wherein: The second subnetwork comprises a mobile radio network, and wherein the third subnetwork is an IP-based transit network.

9. The method according to claim 8, wherein: The mobile radio network is a 5G mobile radio network.

10. The method according to any one of claims 1 to 2, wherein: The MRP interconnection topology change signal is sent out with the help of the MRP_InTopologyChange frame, wherein the data link layer address tables are respectively designed in the form of forwarding databases, and wherein, by sending the MRP interconnection topology change signal, relearning of the respective forwarding databases of the communication devices is triggered in all communication devices of the first subnet.

11. The method according to any one of claims 1 to 2, wherein: By sending the MRP interconnection topology change signal, re-learning of at least one data link layer address assigned to the first endpoint of the data link layer tunnel is triggered in the routers along the data link layer tunnel.

12. A communication system for executing the method according to any one of claims 1 to 11, the communication system comprising: - a first subnet (1), comprising at least a first communication device (103, 105), a first coupled communication device (101) and a second coupled communication device (102), - a second subnet (2), comprising at least a second communication device (221) and a third coupled communication device (201), - a third subnet (3), comprising at least a first router, a second router and a third router, wherein the first subnet and the third subnet are connected via at least the first router and the second router, and the second subnet and the third subnet are connected via at least the third router, wherein the communication device and the coupled communication device are designed to forward datagrams in the first subnetwork and in the second subnetwork respectively by means of switching, wherein the router is designed to forward datagrams in the third subnet by means of routing, - wherein the first subnet has a ring topology, the first coupled communication device is connected to the first router, and the second coupled communication device is connected to the second router, wherein the first subnetwork is designed to transmit datagrams within the first subnetwork according to the Media Redundancy Protocol, MRP, - wherein the third coupled communication device is connected to the third router and the third coupled communication device has an assigned network layer address, wherein the first coupling communication device and the second coupling communication device are designed to select a master coupling communication device from one another by means of a virtual router redundancy protocol, VRRP, and are assigned a common virtual network layer address, - wherein the first coupling communication device and the second coupling communication device are designed to operate the first coupling communication device or the second coupling communication device which is not selected as the main communication device as a reserve coupling communication device, wherein the coupling communication device is designed to send an MRP interconnection topology change signal when the selection of the main coupling communication device changes or the main coupling communication device fails, - wherein the first subnet is designed to trigger relearning of the data link layer address tables of the respective communication devices in the communication devices of the first subnet by sending an MRP interconnection topology change signal, - wherein the coupling communication device is designed to establish a data link layer tunnel (10) between the main coupling communication device and the third coupling communication device via the first router or the second router and via the third router through the third subnet, and the datagram transmitted from the first communication device to the second communication device is encapsulated in a tunnel data frame (200) within the data link layer tunnel, wherein the tunnel data frame is a VXLAN frame or a second layer tunnel frame of the datagram, and the datagram sent from the first communication device to the second communication device is respectively encapsulated in the tunnel data frame, wherein the coupling communication device is designed to configure a first end point of the data link layer tunnel with a virtual network layer address of the first coupling communication device and the second coupling communication device, wherein the coupling communication device is designed to configure the second end point of the data link layer tunnel with the network layer address of the third coupling communication device.

13. A coupled communication device for executing the method according to any one of claims 1 to 11, wherein: The coupling communication device is designed to: - forwarding the datagram by means of switching within a first subnetwork including the coupled communication device, wherein the subnetwork has a ring topology, - transmitting a datagram in said first subnetwork according to the Media Redundancy Protocol, MRP, a first router connected to the third subnet as a first coupled communication device, or a second router connected to said third subnet as a second coupled communication device, - together with the first coupled communication device or the second coupled communication device, a master coupled communication device is selected from among each other by means of a virtual router redundancy protocol, VRRP, and a common virtual network layer address is assigned, - the first coupled communication device or the second coupled communication device which is not selected as a main communication device operates as a reserve coupled communication device, - when the selection of the primary coupled communication device changes or the primary coupled communication device fails, sending an MRP interconnection topology change signal, - triggering relearning of the data link layer address tables of the respective communication devices in all the communication devices of the first subnet by sending the MRP interconnection topology change signal, - a data link layer tunnel is established between the primary coupled communication device and a third coupled communication device of the second subnet via the first router or the second router and via the third router of the third subnet through the third subnet, and a datagram sent from the first communication device of the first subnet to the second communication device of the second subnet is encapsulated in a tunnel data frame within the data link layer tunnel, wherein the tunnel data frame is a VXLAN frame or a second layer tunnel frame of the datagram, and the datagram sent from the first communication device to the second communication device is respectively encapsulated in the tunnel data frame, - configuring a first endpoint of the data link layer tunnel with virtual network layer addresses of the first coupled communication device and the second coupled communication device, - configuring the second endpoint of the data link layer tunnel with the network layer address of the third coupled communication device.

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