A system comprising: a gas turbine engine; a device (68A, 68B, 68C) disposed within a sub-system component (70A, 70B, 70C) of the gas turbine engine, wherein the device is configured to monitor component performance and function and optionally operates as a control and/or identification device; a shielding disposed about the sub-system component (70A, 70B, 70C); a remote processing unit positioned external to the sub-system component (70A, 70B, 70C), the remote processing unit configured to be in electromagnetic communication with the device (68A, 68B, 68C); a transmission path that extends between the remote processing unit and the sub-system component (70A, 70B, 70C), the transmission path being a protected communication channel for the remote processing unit to communicate with the device (68A, 68B, 68C) through the transmission path, wherein the transmission path includes a waveguide (200; 250); and one or more communication paths integrally formed in/on a component of the gas turbine engine, each communication path being arranged to route a portion of electromagnetic signals communicated from the transmission path to the device (68A, 68B, 68C), characterised by: an interface between the transmission path and the subsystem component (70A, 70B, 70C) adapted to transmit power and signals received through the transmission path to the device (68A, 68B, 68C), wherein the communication with the device (68A, 68B, 68C) through the transmission path is via the interface; an electrical interface device, referred to as EID, operatively connected to the sub-system component (70A, 70B, 70C), the EID being operatively connected to and in communication with the device (68A, 68B, 68C), the device (68A, 68B, 68C) being configured to retain identification, calibration or other operational data associated with the EID to characterise the EID; and an EID interface that operatively connects the remote processing unit with the EID. a gas turbine engine; a device (68A, 68B, 68C) disposed within a sub-system component (70A, 70B, 70C) of the gas turbine engine, wherein the device is configured to monitor component performance and function and optionally operates as a control and/or identification device; a shielding disposed about the sub-system component (70A, 70B, 70C); a remote processing unit positioned external to the sub-system component (70A, 70B, 70C), the remote processing unit configured to be in electromagnetic communication with the device (68A, 68B, 68C); a transmission path that extends between the remote processing unit and the sub-system component (70A, 70B, 70C), the transmission path being a protected communication channel for the remote processing unit to communicate with the device (68A, 68B, 68C) through the transmission path, wherein the transmission path includes a waveguide (200; 250); and one or more communication paths integrally formed in/on a component of the gas turbine engine, each communication path being arranged to route a portion of electromagnetic signals communicated from the transmission path to the device (68A, 68B, 68C), characterised by: an interface between the transmission path and the subsystem component (70A, 70B, 70C) adapted to transmit power and signals received through the transmission path to the device (68A, 68B, 68C), wherein the communication with the device (68A, 68B, 68C) through the transmission path is via the interface; an electrical interface device, referred to as EID, operatively connected to the sub-system component (70A, 70B, 70C), the EID being operatively connected to and in communication with the device (68A, 68B, 68C), the device (68A, 68B, 68C) being configured to retain identification, calibration or other operational data associated with the EID to characterise the EID; and an EID interface that operatively connects the remote processing unit with the EID.