Abstract: In a passive optical telecommunication system in which the signal transmission from a switching center downstream to remote units proceeds in a first stream on a time-division multiplex basis and in which the signal transmission from the remote units upstream to the central switching center proceeds in accordance with a TDMA method in accordance wherewith a remote unit transmits each burst in a synchronized fashion with the assistance of a delay device that is individually set with respect to each remote unit proceeding from the switching center, the remote unit already transmits the bursts before the transmission time required for a desired reception phase relation of the burst in the central switching center only after a rough delay time of a whole system clock period (or system clock periods), and the switching center centrally undertakes a respective individually-dimensioned fine delay of the bursts incoming thereat from each of the remote units into the desired reception phase relation.

Abstract: An optical data network, in which data is exchanged between an active central unit (CU1) and subscriber line units (DU1, DU2, DU3, . . .) using the time-division multiplexing method. The reliability is considerably enhanced by parallel connection of a back-up central unit (CU2). In order to permit a disruption-free switchover between the central units (CU1, CU2), the latter have controllable delay devices (TDL1, RDL1, TDL2, RDL2), so that the delays of the signals to and from the subscriber line units (DU1, DU2, DU3, . . . . ) can be matched with the aid of a special line unit (SDU).

Abstract: A method and apparatus for improving picture quality in multi-dimensional differential pulse code modulation coding wherein at the receiver at the end of an active picture line AZ reconstructed samples C.sub.r are expanded by utilizing auxiliary samples H.sub.c which are allocated to the blanking interval AL and the same auxiliary samples H.sub.c are utilized for encoding at the transmitter of the data. The method and apparatus substantially improves the picture quality by utilizing the techniques of the invention.

Abstract: A circuit for rapidly determining the greatest difference among three binarily represented numerical values also undertakes a classification and coding of the maximum difference within a number of different numerical ranges wherein only the most significant bits of the differences following the operational sign bit are required for such classification. A two-stage logic circuit is used for the classification and coding to which the most significant bits are supplied. The circuit is particularly useful in two-dimensional DPCM coding wherein a switchable quantizer and a quantizer controller are utilized to control the contrast of adjacent picture elements including an overall video display.