This PerfCounter64 counts Line Loss Of Signal Seconds encountered by an E1/T1 interface in the current bin, i.e. seconds where no signal at all was detected on the line. LOS is one of the most serious line alarms an admin can see on a T1/E1, since it usually means a physical cut, unplugged cable, or dead transmitter rather than a marginal error condition. If e1t1StatsLineLOSSs starts incrementing on a T1 that had been error-free, the admin's first move is to check for a physically disconnected cable or a failed line card at either end.