csOc3SectionCurrentSESs is a read-only PerfCurrentCount counter reporting the number of Severely Errored Seconds — a one-second period with a very high error density — that the SONET/SDH Section layer of this OC3 port has recorded in the current 15-minute measurement interval, i.e. right now. A rising count here is the operational signal that a serious optical-signal fault on the section, such as a dirty fiber connector or a degrading laser 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 csOc3SectionCurrentSESs on the SONET/SDH Section layer of this OC3 port every few seconds and watching the count jump upward in real time would immediately suspect a serious optical-signal fault on the section, such as a dirty fiber connector or a degrading laser, and could start a bit-error-rate test before the fault gets worse.