Abstract: A method of accessing a local-area network which allows transmission on a unidirectional ring, of circuit-switched or packet-switched communications organized in hybrid frames, in which overlapping between the beginning of a frame and a residual of the preceding frame which is still to reach its destination is avoided without reporting to a rigid band allotment to the indiviual communications and to a network synchronization system, where a well defined node acts as a master clock. According to the method the individual nodes of the network, access in sequence the transmission line in each frame, maintaining the same order of asynchronous access in the circuit and packet regions.

Abstract: The local network comprises a plurality of active nodes (N1 . . . Nn) placed along a folded unidirectional bus (1) which presents a writing branch (1W) and a reading branch (1R). The nodes present means (RR) for network reconfiguration in the presence of a failure, through an isolation of the parts concerned by the failure, through an isolation of the parts concerned by the failure, and for regular service restoration after the repair, and means (GA) for the implementation of an ordered access protocol, which is based on the physical position of the nodes (N1 . . . Nn) and allows hybrid frames to be transmitted through the bus (FIG. 1).

Abstract: The system comprises a plurality of units arranged along a unidirectional line whereupon information is transmitted relevant to circuit switched and packet switched communications and organized into hybrid frames comprising a region for each communication type. The units comprise devices handling the access to the line which cooperate with one another and with a frame signal generator, centralized or associated with each unit, to implement in distributed way an ordered protocol without collisions in both frame region, based on physical unit location.

Abstract: A variable-band distributed switching node comprises a plurality of independent modules (MU.sub.1 . . . MGm) inserted between subscriber or trunk lines and a common bus (1). Each module includes an input/output portion (IU, HL, SL, PL), processing line information, and an interface (IB) toward the bus which co-operates with the interfaces of the other modules to form hybrid frames on the bus. These frames are each divided into a first region RC, encompassing a plurality of channels assigned to circuit-switched communications, and a residual-band second portion RP shared by packet-switched communications. Such frames are dynamically managed by assigning to each circuit-switched channel a band which can differ in consecutive frames to satisfy the requirements of variable-band sources and by recompacting the channels remaining in region RC after each channel release.

Abstract: The system allows the implementation of packet-switched synchronous speech communications in the network without requiring any centralized device synchronizing all the network stations. To obtain that, the active periods of each station are subdivided into frames each having a duration equal to the time elapsing between the generation to two subsequent speech packets relating to the same communication; once a station has accessed the line for the speech communications, these communications are allotted time slots which are maintained for the whole communication duration. The slots not allotted to speech communications are allotted to data transmission. The access to the line for a speech communication is obtained by the same contention techniques used also for data transmission.

Abstract: A communication system serving a number of nodes, each associated with a group of subscriber terminals, comprises a unidirectional bus bent into a loop to form a transmitting branch and a receiving branch respectively connected by an outgoing coupler and an incoming coupler to all the terminals of a given node. In each node a plurality of detectors on opposite sides of the outgoing coupler monitor the activity of the transmitting branch to determine whether the bus is free from any signal carrier originating at an upstream node, or generated at the node considered, and is thus available for voice or data packets to be sent out. Each terminal includes a receiving unit, responsive to a pre-engagement packet addressed thereto via the incoming coupler, which starts a local time base to establish a succession of frames encompassing each a number of time slots allocated to active speech channels in a voice period of a frame; the remainder of each frame is available for data transmission.

Abstract: Each of several stations served by a common bus in a communication system of the packet-switching type has a layered structure interposed between a user terminal and a port giving access to the bus, this structure including an interface separating a transceiver at a bottom level of the structure from upper levels controlling the establishment, maintenance and termination of temporary signal paths for the transmission of data between stations. The interface is divided into a lower-tier portion, implemented by wired-logic circuitry, and a higher-tier portion, programmed to set up virtual point-to-point data links between its own station and other stations under the control of a microprocessor. The lower-tier portion dialogues with the transceiver and has transmitting and receiving sections with respective buffer memories for the temporary storage of outgoing message frames generated at the higher-tier portion and incoming message frames extracted from the bus and found to be addressed to the station involved.