This preserves how long a now-expired control tunnel had been active, in hundredths of a second, before it terminated, per its description, the historical companion to the live cisgIpsSgTunActiveTime. It's a key metric for judging whether a closed tunnel had a normal, long lifespan or died prematurely - combined with HistLifeTime, an admin can see whether it reached its full negotiated rekey interval or was cut short by some failure. An active time far shorter than the negotiated lifetime is a strong signal that the tunnel's termination reason reflects a real problem rather than a scheduled rekey.