Abstract: A star local-area network system comprises a plurality of data stations and a central switching unit for switching the connection between the data stations.

Abstract: A plurality of radio networks for transmitting data include a head end unit and a plurality of work stations. The head end unit receives a radio signal output from a given work station, converts the reception signal into a radio signal of a different frequency, and re-radiates the signal to all the work stations. Each work station includes a data processor, a receiving section for receiving and demodulating the radio signal from the head end unit to obtain data supplied from another work station, and supplying the obtained data to the data processor, and a unit for receiving transmission data generated by the data processor, and converting the transmission data into a radio signal and radiating the radio signal, thereby transmitting the transmission data to another work station through the head end unit.

Abstract: According to this invention, a limited multicast communication notice indicating that an identical message is transmitted to a plurality of arbitrarily designated stations is transmitted prior to transmission of a text message. The notice includes definition data. The notice is received by a data input/output section, and it is checked by a comparator if the notice is a message destined to be sent to the intrastation. If it is discriminated that the notice is destined to be sent to the intrastation, the notice is received, and the definition data in the notice is held in the comparator. Thereafter, a CPU forms a response message and sends it to a source station. Thereafter, a text message is transmitted using limited multicast transmission. It is checked by the comparator if the received message includes the same definition data held in the comparator. As a result, if the received message includes the definition data, the message is received by the serial input/output section and is stored therein.

Abstract: In a communication system for a local network, in which a plurality of host computers are connected to a coaxial cable through respective controllers and transceivers, each controller, as soon as it has received a text frame, transmits an acknowledgement frame to the transmitting side controller. The transmitting side controller transmits a first dummy frame after the completion of the text frame transmission until a collision on the line is detected. The receiving side controller transmits a second dummy frame from the instant of completion of the text frame reception to positively cause a collison. When the collision is no longer detected, the receiving side controller stops the transmission of the second dummy frame and transmits an acknowledgement frame immediately afterwards.