This TimeTicks value records sysUpTime at the moment the interface entered its current operational state, reading zero if that state was entered before the last reinitialization of the local management subsystem. An admin uses this to determine how long a DS0 interface has held its current up/down state, helping correlate a state change with a recent event. For example, a recent ctDs0ifLastChange value on an interface that just alarmed would confirm the state change happened at roughly the time of a reported line fault.