Abstract: A communications system interconnects a number of asynchronous data processing terminals, operating at different speeds among themselves, with a high speed switching or communication network. The system uses as a time multiplexed loop linking terminals which are later duplicated for security reasons. The number of terminals that may be hooked up may exceed that which would be provided if all terminals were to be active simultaneously. For this purpose, a signalling or watch function is used in the system to monitor the state of each terminal. This function, which assumes the active (busy) or rest (idle) state of the terminals, is based on a low speed search for terminals at rest, on detecting the change in their states and on the time sharing allocation, of the time multiplexed transmission resource among the active terminals according to their needs. The time sharing of the transmission resource is adaptive.