A modular, expandable, non-blocking system for cross-connecting high speed digital signals is provided. The system is capable of connecting DSn, CEPTn, and STSn signals as desired, with lower rate signals being included as components of the high-rate signals or terminating on low speed lines, as desired. The system accomplishes its goals by converting all incoming signals into a substantially SONET format, and by processing all the signals in that format. The signals are typically cross-connected in the substantially SONET format, although an expandable non-blocking wide band cross-connect module is provided which cross-connects any like signals. If the outgoing signal is to be in other than SONET format, the substantially SONET formatted signal is reconverted into its outgoing format. To create a complete system, various modules are utilized, including: add/drop multiplexer means for add/drop applications of DS-0, DS-1, CEPTn signals, etc.; a SONET bus interface; a virtual tributary cross-connect module which cross-connects virtual tributary payloads in space, time, and phase to generate new substantially SONET formatted signals; a wide band cross-connect module; a DS-3/SONET converter; and front end interfaces including a DS3 line interface, and various STSn interfaces. The modules may be mixed and matched as desired to accommodate a multitude of applications.