EXFO FTB/IQS-85100G Packet Blazer for FTB-500/IQS-600 - Manual (Page 231)

Test Results
Packet Blazer 221
Performance Monitoring

UAS (Unavailable Second): Gives the count of the seconds
corresponding to the period of unavailable time that begins at the
onset of 10 consecutive SES events, including these 10 seconds. A
period of available time shall begin at the onset of 10 consecutive
non-SES events, including these 10 seconds.

ESR (Errored Second Ratio): Gives the ratio of the number of ES in
available time to total seconds in available time during a fixed
measurement interval.
ESR = ES ÷ AS

SESR (Severely Errored Second Ratio): Gives the ratio of the number of
SES in available time to total seconds in available time during a fixed
measurement interval.
SESR = SES ÷ AS

BBER (Background Block Error Ratio): Gives the ratio of BBE in
available time to total blocks in available time during a fixed
measurement interval. The count of total blocks excludes all blocks
during SESs.