Severely Errored Seconds (SES) is a unit used to evaluate the error performance of T-lines
. The Severely Errored Seconds refers to a one-second interval in which the error rate is greater than the specified error rate
and thus affects the transmission performance. The SES unit can refer to errors per time unit in seconds, hours, days or weeks. This method allows a better evaluation of the error distribution than the simple bit error rate (BER).