System for detecting failure in dual bus user network

摘要

System for controlling access competition among a plurality of terminals under the DQDB protocol in a B-ISDN where the terminals are electrically connected to a dual bus with a downbus and an upbus extending from a network terminal. Each of the terminals has data transmission processor, downbus processor, upbus processor, a timer and failure detector. When data transmission request is issued from the data transmission processor, the failure detector is activated in response to a request to start the timer so as to count a given time interval which has elapsed. If either a request message or data cannot be sent even when the timer reaches a predetermined value, the failure detects signals that a failure has occurred in the dual bus.