A DS3 Severely Errored Framing Second (SEFS) is a
count of one-second intervals containing one or
more SEF events. A Severely Errored Framing (SEF)
event is declared when an error in the A1 octet
and an error in the A2 octet of a framing octet
pair (i.e., errors in both framing octets), or two
consecutive invalid and/or nonsequential Path
Overhead Identifier octets are detected.