the present disclosure relates to a system comprising at least a first and a second essentially analogue portion and an essentially digital portion , the analogue portions forming a part of a unidirectional circular network . first communication means is provided between the digital portion and the first analogue portion . second communication means is provided between the first and second analogue portions . the first and second communication means are configurable for establishing communication between the digital portion and the second analogue portion . the first and second communication means are arranged to determine if a packet communicated over the first or second communication means is of interest for any of the analogue portions .