a self - routing communication network having : a plurality of nodes ; a plurality of star couplers each having a plurality of inputs and a plurality of outputs ; and communication paths coupled between the plurality of star couplers and the plurality of nodes for communication therebetween of frames of information , including at least one redundant communication path , and each of the star couplers sensing which of its inputs first receives a frame and passing only the frame first received . the frames each have a fram - start - sequence , and the star couplers change the fram - start - sequences before outputting the frame of information e . g . by reducing the size of a frame &# 39 ; s fram - start - sequence by a predetermined amount , whereby interconnection failure may be diagnosed by analyzing the frame - start - sequence .