What causes timing reference switches? In other words, when is a timing reference disqualified?
A. Timing reference switches can be caused by these factors: • The optical or Building Integrated Timing Supply (BITS) input experiences Loss of Signal (LOS) alarms, Loss of Frame (LOF) alarms, Alarm Indication Signal (AIS) alarms, or the interface is out of service. • The Synchronous Status Messaging (SSM) indicates Do Not Use for Synchronization (DUS) alarms, or the SSM indicates that the clock is of Stratum-3 (ST-3) or lower quality. • The input frequency is off by more than 10 ppms. • The input clock is unstable (wandering). • The reference has not been valid for at least two minutes.
