EXFO FTB-8500 Series for FTB-200 - Manual (Page 336)

Common Tab
322 FTB-8500 Series and FTB-8120NGE/8130NGE
Performance Monitoring (PM)

SESR (Severely Errored Second Ratio): Gives the ratio of the number of
SES in available time (AS) during a fixed measurement interval.
SESR = SES ÷ AS

BBER (Background Block Error Ratio) (G.826 only): Gives the ratio of
BBE in available time (AS) to total frames (fps - Frames per second) in
available time during a fixed measurement interval. The count of total
frames excludes all frames during SESs.
BBER = BBE ÷ ((AS - SES) * fps)