Optical data network having adjustable delays for switching over to backup unit

Claim 1

An optical data network having an active central unit connected between a switching device and an optical subscriber line network and a plurality of subscriber line units connected by optical waveguides and couplers, each of which transmit or exchange data via the active central unit using a time-division multiplexing method, comprising: at least one further back-up central unit connected functionally in parallel with the active central unit, the central units being connected to the subscriber line network by optical waveguides; each of the central units having a controllable transmission delay device in a transmission path thereof and a controllable reception delay device in a reception path thereof, the reception delay device of the back-up central unit being set by received signals; at least one special line unit connected to the subscriber line network, which special line unit has a controllable delay device in a transmission path thereof; the special line unit having in a reception path thereof a measuring device for determining the delay difference between send signals of the active central unit and of the back-up central unit; and the special line unit transmitting a correction signal, by means of which the transmission delay device of the back-up central unit is controlled until delays for the send signals of both central units are the same.