Appendix E – Performance Analysis Options
Page 140 Acterna ANT-5
G.821 definitions:
• Errored second (ES): A one-second time interval in which one or more bit errors
occurs.
• Severely errored second (SES): A one-second time interval in which the bit error
ratio exceeds 10
-3
.
• Unavailable second (UAS): A circuit is considered to be unavailable from the first of
at least ten consecutive SES. The circuit is available form the first of at least ten
consecutive seconds which are not SES.
• Degraded minute (DM): A one-minute time interval in which the bit error ratio
exceeds 10
-6
.
• Error-free second (EFS): A one-second time interval in which no bit errors occur.
The disadvantage of G.821 is that it relies on the evaluation of bit errors and so the
test channel must be taken out of service to perform the measurement.
13.2.2 Recommendation G.826
This Recommendation takes higher bit rates into account and allows in-service
measurement as it relies on the evaluation of block errors.
G.826 definitions:
• Errored second (ES): A one-second time interval containing one or more errored
blocks.
• Errored block (EB): A block containing one or more errored bits.
• Severely errored second (SES): A one-second time interval in which more than 30%
of the blocks are errored or which contains at least one severely disturbed period
(SDP).
• Background block error (BBE): An errored block that is not a SES.
• Unavailable second (UAS): see under G.821 above.
The results are referred to the measurement time. This gives the following error
parameters: Errored seconds ratio (ESR), severely errored seconds ratio (SESR), and
background block error ratio (BBER). The specified quality requirements refer too a
particular path.
The recommended measurement time for G.821 and G.826 is 30 days.
13.2.3 Recommendation G.828
Unlike G.826, recommendation G.828 provides a precise block length for each bit
rate. For example, the number of blocks monitored per second for bit rates from VC3
upwards remains constant at 8000.
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