Abstract: Failure of a local exchange in a communications network (such as the PSTN) is detected by monitoring a combination of parameters. Each parameter in the combination is monitored for meeting predetermined criteria. In particular, a local exchange failure is recognized when the average value of the All Circuits Engaged (ACE) parameters over all traffic routes into a local exchange rises in a significant manner and the average value of the Circuits in Service (CCTS IS) parameters over all traffic routes into that exchange decreases in a significant manner.

Abstract: In a telecommunications network, such as the public switched telephone network, account must be taken of faults which can occur in the network. For instance, on occurrence of a local exchange failure, it is known to apply control such as route gapping and code blocking. The invention is concerned with detection of failure of a local exchange (116, 118) in a communications network. It relies on a combination of parameters, each parameter in the combination having to meet predetermined criteria. In particular, a local exchange failure is recognized when the Bids per Circuit per Hour (BCH) along selected traffic routes exceed a first threshold and the magnitude of a decrease in the average Answer Seizure Ratio (ASR) on selected traffic routes exceeds a second threshold. Controls might be applied to parent or far-end trunk exchanges, and can be removed when the ASR and Percentage Occupancy (OCC) meet further criteria.