csDs3Ds1CurrentESs is a read-only PerfCurrentCount counter reporting the number of Errored Seconds — a one-second period containing at least one CRC error or other defect — 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 ordinary transmission errors on the DS1 channel 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 csDs3Ds1CurrentESs 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 ordinary transmission errors on the DS1 channel, and could start a bit-error-rate test before the fault gets worse.