The state of the art in fully electronic space-division telephone exchanges shows that neither can semiconductor crosspoints directly replace reed relay contacts in Public exchanges, nor can hitherto semiconductor switching networks compete with reed relay switching networks. Though semiconductor crosspoints fulfill all transmission requirements, they are too expensive. Investigations on this field by the authors led to the following results. 1) A semiconductor crosspoint with high breakdown voltage and low on-resistance has been developed. This crosspoint can be connected to a subscriber's line and thus directly replace a reed relay in a public exchange at only slightly higher cost. 2) These crosspoints with high voltage capability can be combined with low cost, low breakdown voltage MOS semiconductor arrays in large-scale integration (LSI) techniques which are isolated from the subscriber lines by transformers to form a fully electronic switching network. 3) A crosspoint free of on-attenuation which can be monolithically integrated to crosspoint arrays has been developed; 4) A thick-film hybrid crosspoint for switching of commercial high-resolution video signals has been developed. The state of the art of optical switching systems shows that switching networks using a laser beam enable the transmission of wideband video signals with comparatively high crosstalk attenuation.

A survey of recent German research in the field of picture coding is presented. The described coding methods are mainly based on extended differential pulse-code modulation (DPCM) techniques. A unified model of a feedback switched quantizer for picture coding is explained. Theoretical results show a 9-dB gain in SNR over that of DPCM. A simple realization is shown. For encoding the 1-MHz videotelephone signals, a two-stage coding system consisting of a two-dimensional DPCM in the first stage and a dot interlaced frame repeating codec in the second stage is described. A DPCM combined with a relevancy detector and runlength coder is used for coding the 5-MHz video signals of a high-resolution videotelephone. A special scanning technique assures compatibility with ordinary videotelephones. Good picture quality is obtained by coding the luminance and chrominance signals of color TV separately with DPCM and switched quantization into a 34 Mbit/s signal.

A purely branched network with decentralized switching using glass fiber channels is discussed. A concise survey is given of the possibilities applying wide-band transmission lines, especially glass fibers, in a communication system, with regard to the integration of services. A purely branched wide-band network with subscribers connected to the lines according to the method of time division multiple access shows some considerable advantages in comparison with conventional systems. A particular system based on this procedure is described Where each subscriber's station has its own control unit instead of a centralized common control. Multiplexing, network synchronization, and the algorithm to set up a connection are explained. It is shown that this system automatically adapts the distribution of low-band transmission channels and wideband channels to the traffic offered.