A system comprising: a gas turbine engine ; a device disposed within a sub-system component 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 ; a remote processing unit positioned external to the sub-system component , the remote processing unit configured to be in electromagnetic communication with the device ; a transmission path that extends between the remote processing unit and the sub-system component , the transmission path being a protected communication channel for the remote processing unit to communicate with the device 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 , characterised by : an interface between the transmission path and the subsystem component adapted to transmit power and signals received through the transmission path to the device , wherein the communication with the device through the transmission path is via the interface; an electrical interface device , referred to as EID, operatively connected to the sub-system component , the EID being operatively connected to and in communication with the device , the device 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 disposed within a sub-system component 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 ; a remote processing unit positioned external to the sub-system component , the remote processing unit configured to be in electromagnetic communication with the device ; a transmission path that extends between the remote processing unit and the sub-system component , the transmission path being a protected communication channel for the remote processing unit to communicate with the device 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 , characterised by : an interface between the transmission path and the subsystem component adapted to transmit power and signals received through the transmission path to the device , wherein the communication with the device through the transmission path is via the interface; an electrical interface device , referred to as EID, operatively connected to the sub-system component , the EID being operatively connected to and in communication with the device , the device 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 . <EOS>