Abstract: The invention relates to, among other things, a method according to which an access function (36) for a number of service user computers (18) permits a connection between the service user computer (18) and a service provider computer (22 to 26), which is selected by a service user (A), according to requests submitted by a service user computer (18). The insertion of an access function (36), and the use of a test unit (38) make it possible to secure useful data that is to be processed in a reliant manner.

Abstract: A public communication system for a plurality of communication services (ISDN) has an arrangement for the authentification of the subscriber stations (TLN A, TLN B) for the key transmission.

Abstract: In order to prevent bit combinations which are assigned to specific control characters from arising when ciphering characters, transmittable characters which consist of a part of the ciphered character and fill characters are generated from the ciphered characters. When the ciphered characters respectively consists of m binary characters, respectively small n binary characters from a sequence of ciphered characters are provided with (m-n) fill characters and combined to form the transmittable characters. The binary values of the fill characters are selected in such a manner that no undesired control characters occur within the transmittable characters and given specific sequence of transmittable characters.

Abstract: A transmission code required for decoding an encoded transmission of messages between a transmitting station and a receiving station is first transmitted from one station to the other. Previously identified passwords are used to encode the transmission code, by the transmitting station, together with a transmission station code. At the receiving station, a code signal is decoded with the password and reencoded with a receiving station code and with an additional password. The transmitting station receives the encoded acknowledgement from the receiving station, decodes the acknowledgement using the second password, and its own station code, and reencodes it with a third password, transmitting the result back to the receiving station. The receiving station extracts the transmission code from the second transmission from the transmitting station, by decoding it with the receiving station's station code and the third password.

Abstract: Circuit arrangement for the correction of data transmitted over a communication channel incorporates a shift register and a parity stage at the transmission side of the channel for generating parity bits, and similar equipment located at the reception side of the channel for generating similar parity bits. The parity bits are compared to provide syndrome signals, and the syndrome signals are stored in a syndrome shift register having a plurality of taps. A majority stage is effective to make corrections in the transmitted data when a majority of the syndrome signals at the taps of the syndrome register indicate an error condition. The taps of the shift registers employed for the parity generation and the taps of the syndrome shift register are spaced at unequal intervals. Four, six or eight taps are employed.

Abstract: Apparatus is described for monitoring and, if necessary, correcting the polarity of a transmitted data signal. Syndrome signals are produced in accordance with the error pattern of the transmitted data signal. Coincidences between block timing pulses and the syndrome signal and block timing pulses and an inverted syndrome signal are counted, and when the respective counts reach predetermined levels counted output signals are produced. A polarity signal indicating proper or improper data signal polarity is produced from the counted output signals. The polarity of the transmitted data signal is adjusted in accordance with the value of the polarity signal.

Abstract: A method is described for testing the transmission quality of a data transmission system in its operational state. During a test key actuation data bits having a specific marking polarity and at least one additional bit having a polarity corresponding to the spacing condition are transmitted. At a receiving station the latter transmitted bit group is analyzed for disturbances. In the event of multiple undisturbed reception of the aforementioned bit pattern a visual indication is produced. At the same time, in the receiving station, the data output of the receiver is connected to the transmitter, and the aforementioned bit pattern is transmitted back to the testing station. With multiple undisturbed reception of the bit pattern a visual indication is produced in the testing station. During the test procedure the data input and output units are blocked.

Abstract: A circuit arrangement is described for carrying out a diversity selection from a number of data channels. The diversity channels are connected to a majority logic decision stage. The diversity channels and the output from the majority logic stage are connected to a channel switch as data channels. By means of a quality evaluation stage, one of the diversity channels is switched through to the data bank under the control of signals produced responsive to an indication that a minority of the diversity channels is better than each of the remaining diversity channels by a given quality difference. The majority decision channel is switched through with one of the control signals when the majority of the diversity channels are poorer than the remaining diversity channels during the given test period by another given quality difference.

Abstract: A method is described for establishing character frame synchronism between a teletypewriter transmitter and receiver wherein the direction of transmission is unidirectional. The transmitter sends character signals identifying characters of the alphabet or the like and operating condition signals corresponding to the operation condition of the transmitter. The operating condition signals are processed in a code converter which allocates code words to them permitting recognition of the character frame. The code words are transmitted to the receiver wherein a clock signal is derived by means of a character frame discriminator. The code words are reconverted in the receiver in order to cancel the code conversion which took place at the transmitter.

Abstract: Apparatus for selecting a diversity channel in a data processing system is described. Data from a data source are assigned a signal whose binary values change within a given test period. At the receiver, a test device produces test signals indicating parameters of the received signals, and in dependence upon the test signals one of the diversity channels is connected by a channel switch to a data sink.