Abstract: In a ring communication system comprising several stations, access to the ring is granted to one station at a time by a circulating token indication. A method is provided guaranteeing a transmission opportunity for synchronous or circuit-switched data in periodic time intervals to authorized stations. A CS monitor station issues a frame header which is marked in a specific bit position to allow only authorized stations to transmit their synchronous data together with a destination address. In a first embodiment, a single frame comprises a plurality of slots each having a free/busy indication, a destination address field and a field for synchronous data, and each authorized station can occupy one such slot. In a second embodiment, a marked frame can be used by only one authorized station for transmitting synchronous data, but a new marked frame header is reissued until all authorized stations around the ring have transmitted synchronous data.

Abstract: A processor intercommunication system includes a plurality of stations which are interconnected by a transmission link, each station having an associated processor. Further, each station comprises means which provide a data link protocol mechanism for establishing and maintaining a multiplicity of logical connections or transfer sessions between the station and several other stations. Thus application programs of all kinds in the processors can communicate with programs or data files in remote processors and need not be involved in communication operations which are handled by the stations. Link access circuitry is provided also in each station for absorbing the physical and topological characteristics of the transmission link so that the data protocol circuitry establishing and maintaining logical connections is independent of these characteristics.

Abstract: In a loop-structured communication system interconnecting a plurality of data processors without central controller, stations comprise modems which can start loop operation and achieve synchronous frame transmission around the loop through all participating stations.In an initialization procedure after system start or after loss of frame synchronization on the loop, modems select a temporary master station.The temporary master will adapt total loop delay to be an integer multiple of the basic frame period, and will transmit available frames. All active modems adapt their timing to the circulating stream of frames until the whole loop and all participating stations are synchronized.Synchronization conditions are continuously monitored in all stations to start resynchronization or initialization procedures if necessary. In a specific arrangement, the location of a loop failure which prevents establishment of synchronization can be determined.

Abstract: A synchronous data transmission system between remote stations is shown wherein data is transmitted parallel by bit serial by group over a plurality of parallel lines extending between sending and receiving stations. A parity line is also included in the transmission system for checking errors and a clock line is included for synchronization of the parallel data being transmitted. Information is transmitted from one station to another with alternating even and odd parity for succeeding groups of parallel data. The information is checked at the receiving station for even-even or odd-odd parity in succeeding groups of data. Longitudinal redundancy checking (LRC) is also added to the checking at a receiving station. The combination of the even and odd parity checking and the LRC checking provides a level of data transmission error checking which is almost as effective in finding errors as a far more costly CRC checking mechanism.