Method and apparatus for controlling access to a communication network

摘要

A communication system comprises several transmission bus segments (A . . . G) to which data stations (ST) are attached. Node units (1 . . . 7) are provided for interconnecting the bus segments which are selectively activated in a predetermined sequence for authorizing message transmission by attached data stations according to any given access protocol. Thus, only small groups of stations contend for access, but all messages are distributed over the whole network. Activation of a bus segment is effected by an authorization message from an assigned node unit. A token message is used to pass the status enabling a node to activate its assigned bus segment, sequentially through all nodes of the network. Each node unit comprises a control unit (17) for sending and receiving token messages and segment activation messages, and further comprises unidirectional amplifier means and switches (11) for establishing a connection between two associated bus segments selectively in either direction.