The principles and protocols of APS in SONET networks are defined in ITU-T G.783 and G.841 and Bellcore GR-253
recommendations for Linear and Ring network architectures respectively. According to these recommendations, the re-routing of
the signal has to occur within 50ms. Protection switching is initiated as a result of one of the following conditions;
-
“Hard” Failure (SF) condition – Loss of Signal (LOS), MS-AIS, BER >1 x 10
-3
- “Soft” Failure (SD) condition – Signal degradation when BER exceeds a predetermined threshold. Normally over a
provisioned range of 1 x 10
-5
to 1 x 10
-9
Test Procedure:
1. The TX150 should be connected to a tributary port of network element or transmission system to ensure that the
switching time is measured for the service transported by the SONET network.
2. Ensure that no errors or alarms are present on the transmission system because this will impact the
measurement.
3. The measurement will be triggered by an Alarm Indication Signal (AIS)
4. The TX150 measures how long the AIS event remains present after the event is first recognized and will
continue to measure the total disruption time in the event of multiple disruptions.
TX150 e-Manual D07-00-023 Rev A02
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