Variable-band switching system for voice and data communication

A communication system wherein a plurality of nodes are associated with respective groups of subscriber terminals adapted for the exchange of speech and data packets via a common unidirectional bus forming a loop with a transmitting branch and a receiving branch passing through all said nodes,

• each node comprising an outgoing coupler and an incoming coupler linking all the terminals of the associated group with said transmitting branch and said receiving branch, respectively;
• first and second detecting means in each node respectively disposed upstream and downstream of said outgoing coupler in said transmitting branch for recognizing the presence of signal carriers on said transmitting branch originating at any node upstream of a given node and at the given node itself and
• logic circuitry at each terminal comprising a receiving section coupled to said incoming coupler, a transmitting section coupled to said outgoing coupler and control section coupled to said first detecting means, said second detecting means, said incoming coupler, said receiving section and said transmitting section, each terminal further comprising means connected to said transmitting section, for generating and storing speech packets, data packets and pre-engagement packets and for informing said transmitting section of the availability of such packets to be sent out, and means coupled to said receiving section for storing received speech packets, data packets and pre-engagement packets, said control section being responsive to signals from said first and second detecting means for enabling said transmitting section to send out a waiting packet in the absence of conflicting activity on said bus, said receiving section being responsive to the arrival of a pre-engagement packet addressed thereto for starting a time base in said control section to initiate a series of frames with a duration at least equal to the recurrence period of consecutively generated speech packets certaining to a particular voice communication between two terminals, said time base subdividing each frame into a voice period for the emission of at least one speech packet in an allocated time slot and a residual period reserved for the emission of data packets, said series of frames terminating in the absence of further packets to be sent out whereupon another terminal of the same node or of a node further downstream along said transmitting branch can send out packets in the course of a round giving all terminals successive access to said transmitting branch.