Abstract: A digital concentrator includes line circuit modules (3,4) and provides time-division multiplex (TMD) channel set-ups between a bus (5), connected to all modules, and PCM links (1), each going from its own module, the number of links being less than the number of modules, as well as between groups of subscriber lines (2), connected to the modules, and the bus (5), and between the subscriber line group and the link being connected to the same module (4). The bus must always be used for a set-up to an arbitrary link from a subscriber line, the line circuit module (3) of which is solely connected to the bus (5). In order to avoid congestion on the bus as far as possible the bus is only used for a set-up to an arbitrary link from a subscriber line, the module (4) of which is connected to the bus (5) and to one of the links (1), solely if a given number of the TDM channels of the link associated with this module are already busy.

Abstract: Arrangement in data transmission between a transmitting computer, sending signal words containing start-stop information, message words and address-control signal information, and a receiving computer, for providing separate supervision of faults on the transmission lines and of such errors which are caused by faults in the signal equipment pertaining to the computer of the transmitter side, intermediate stations or the computer on the receiver side. The arrangement includes means for generating and checking two check sums which are mutually supplementary, an inner check sum (S) for monitoring the hardware incorporated in computers and intermediate stations on a transmission path, and an outer check sum (YS) for monitoring the transmission lines. The inner check sum is formed by adding all the message words in a complete signal word; and the outer check sum is formed by adding the address-control signal information, message words and the inner check sum.