This counter logs the number of AIS (Alarm Indication Signal) cells received on the Virtual Channel Link, which are diagnostic signals sent by the far end to indicate a failure or alarm condition on their side. Network engineers watch this counter to detect when the remote switch is reporting problems, and an increase signals that the remote side has detected a fault and is alerting this switch to stop sending data. For example, if a normally-zero AIS counter suddenly jumps to 100 cells in one minute, the remote ATM switch is in alarm and this switch should attempt to reroute traffic to another circuit.