A diagnostic system for a telecommunications system including a digital switching network is controlled via a plurality of data processors. Each of the distributed data processors has a unique address and has diagnostic data stored therein for use in performing diagnostics in the switching network. The switching network includes digital switching elements, each having bidirectional ports for receiving and transmitting digital signals, and each of the bidirectional ports also having a unique address in the network. Diagnostic paths are established under processor control between the digital switching elements and the data processors. Each of the data processors is interconnected to another data processor by connection paths equal in number to the number of bidirectional communication paths originating from such data processor so that the addresses of the data processors are algorithimically related to the addresses of the bidirectional ports interconnected by the diagnostic paths, thereby achieving a simplified and reliable protocol for data transfer from processor to processor.