Abstract: Multiplex time division switching network unit comprising a plurality of P groups of N incoming and outgoing multiplex highways and P incoming and outgoing supermultiplex highways each formed of N multiplex highways and having 2aN time slots where a is the number of time slots in a multiplex highway. The supermultiplex highways are multiplexed two by two and with themselves to form double supermultiplex highways each having 2aN time slots. It results that there exists a double supermultiplex highway simultaneously containing any time slot assigned to a calling party and any time slot assigned to a called party whatever be these time slots. The buffer stores of the switching network unit can thus be rendered bidirectional and their number is P(P+1)/2 instead of P.sup.2 in the prior art.