Self-checking network device for communication in a real-time network, wherein • the self-checking network device is connected to two or more communication links, and • the self-checking network device exchanges regular data and protocol data with other network devices (201, 202, 203) and/or nodes of the real-time network using the two or more communication links, and • said protocol data is communicated as part of one or more certain network protocols, characterized in that • the self-checking network device comprises at least four modules (S-COM, P-COM, P-MON, S-MON), wherein the self-checking network device is configured in a way that • a first module (S-COM) of the at least four modules receives both regular data and protocol data from said communication links on a first input (COM-IN), and • said first module (S-COM) forwards protocol data on a second input (P-COM-IN) to a second module (P-COM) of the at least four modules, wherein • said second module (P-COM) executes a first function (C-PU) as part of the one or the more certain network protocols, using protocol data received on said second input (P-COM-IN) and produces protocol data as output on a first output (P-COM-OUT), and • a third module (P-MON) of the at least four modules monitors said second input (P-COM-IN) and said first output (P-COM-OUT) of said second module (P-COM), and wherein • said third module (P-MON) executes protocol checks (P-CHK) on said second input (P-COM-IN) and said first output (P-COM-OUT) and executes a safe action (P-SA) in case that said protocol checks (P-CHK) indicate that said second module (P-MON) does not confirm to rules of said one or more certain network protocols, and • in the case that said third module (P-MON) does not execute a safe action (P-SA), protocol data produced by said second module (P-COM) on said first output (P-COM-OUT) is provided on a third input (P-COM-MON-OUT) to said first module (S-COM), and • said first module (S-COM) executes regular operations (C-SW) on regular data and on protocol data received from said third input (P-COM-MON-OUT), and • a fourth module (S-MON) of the at least four modules monitors the first input (COM-IN), the second input (P-COM-IN), the third input (P-COM-MON-OUT) and the second output (COM-OUT) of said first module (S-COM), and wherein • said fourth module (S-MON) executes regular data checks (S-CHK) on said first input (COM-IN), on said second input (P-COM-IN), on said third input (P-COM-MON-OUT) and on said second output (COM-OUT) and executes a safe action in case that said regular data checks (S-CHK) indicate a failure of the said first module (S-COM), and wherein • in the case that said fourth module (S-MON) does not execute a safe action, the self-checking network device provides protocol data and/or regular data received on said second output (COM-OUT) to the one or more communication links. • the self-checking network device is connected to two or more communication links, and • the self-checking network device exchanges regular data and protocol data with other network devices (201, 202, 203) and/or nodes of the real-time network using the two or more communication links, and • said protocol data is communicated as part of one or more certain network protocols, characterized in that • the self-checking network device comprises at least four modules (S-COM, P-COM, P-MON, S-MON), wherein the self-checking network device is configured in a way that • a first module (S-COM) of the at least four modules receives both regular data and protocol data from said communication links on a first input (COM-IN), and • said first module (S-COM) forwards protocol data on a second input (P-COM-IN) to a second module (P-COM) of the at least four modules, wherein • said second module (P-COM) executes a first function (C-PU) as part of the one or the more certain network protocols, using protocol data received on said second input (P-COM-IN) and produces protocol data as output on a first output (P-COM-OUT), and • a third module (P-MON) of the at least four modules monitors said second input (P-COM-IN) and said first output (P-COM-OUT) of said second module (P-COM), and wherein • said third module (P-MON) executes protocol checks (P-CHK) on said second input (P-COM-IN) and said first output (P-COM-OUT) and executes a safe action (P-SA) in case that said protocol checks (P-CHK) indicate that said second module (P-MON) does not confirm to rules of said one or more certain network protocols, and • in the case that said third module (P-MON) does not execute a safe action (P-SA), protocol data produced by said second module (P-COM) on said first output (P-COM-OUT) is provided on a third input (P-COM-MON-OUT) to said first module (S-COM), and • said first module (S-COM) executes regular operations (C-SW) on regular data and on protocol data received from said third input (P-COM-MON-OUT), and • a fourth module (S-MON) of the at least four modules monitors the first input (COM-IN), the second input (P-COM-IN), the third input (P-COM-MON-OUT) and the second output (COM-OUT) of said first module (S-COM), and wherein • said fourth module (S-MON) executes regular data checks (S-CHK) on said first input (COM-IN), on said second input (P-COM-IN), on said third input (P-COM-MON-OUT) and on said second output (COM-OUT) and executes a safe action in case that said regular data checks (S-CHK) indicate a failure of the said first module (S-COM), and wherein • in the case that said fourth module (S-MON) does not execute a safe action, the self-checking network device provides protocol data and/or regular data received on said second output (COM-OUT) to the one or more communication links.