Definition of SDH bit error performance

Definitions of SDH bit error performance:
Background block error (BBE):
an errored block not occurring as a part of an SES.
Errored second (ES):
Errored bit second: interval of 1 second during which a given digital signal is received with one or more errored bits according to G.821.
Errored block second: interval of 1 second during which a given digital signal is received with one or more errored blocks according to G0.826.
Errored second: errored bit second and errored block second.
Severely errored second (SES):
Severely errored bit second: interval of 1 second during which a given digital signal is received with an error bit ratio greater than 1 x 10-3 according to G.821
Severely errored block second: interval of 1 second during which 30% or more errored blocks exist or at least one defect exists according to G.826.
Unavailable second (UAS):
Unavailable second: An unavailable period starts from the first second of 10 consecutive SES events. These 10 seconds are considered as a part of the unavailable seconds. A new available period starts from the first second of 10 consecutive non-SES events. These 10 seconds are considered as a part of the available seconds.
Consecutive severely errored second (CSES):
Consecutive severely errored second: 2 to 9 consecutive SES events.

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