This value, accessible only via notification, holds the previously received Synchronization Status Message on this interface and is used specifically by the syncStatusMsgChanged trap. Admins use this trap variable to see what the SSM value was immediately before it changed, giving before/after context for a timing-reference change event. For example, this object reporting a value corresponding to a higher-quality clock than the new syncStatusMsgRxMessage would show the interface's received timing quality just degraded.