csDs3Ds1CurrentCSSs is a read-only PerfCurrentCount counter reporting the number of Controlled Slip Seconds — a one-second period in which the receive buffer slipped a frame because transmit and receive clocks were not synchronized — that this channelized DS1 (T1) circuit carried inside the DS3 has recorded in the current 15-minute measurement interval, i.e. right now. A rising count here is the operational signal that a clock-source mismatch between this DS1 channel and its far end is happening on that interface, which is exactly the kind of degradation a monitoring admin wants an early warning of before it causes an outage. For example, an admin polling csDs3Ds1CurrentCSSs on this channelized DS1 (T1) circuit carried inside the DS3 every few seconds and watching the count jump upward in real time would immediately suspect a clock-source mismatch between this DS1 channel and its far end, and could start a bit-error-rate test before the fault gets worse.