VeEX RXT3900, User Manual

Page: 141 / 383

The protection mechanism is coordinated by the K1 and K2 bytes in the Multiplexer Section Overhead.
APS Standards
The principles and protocols of APS in SDH 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 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.
APS Test Procedure:
The test set 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.
Ensure that no errors or alarms are present on the transmission system because this will impact the measurement.
The measurement will be triggered by an Alarm Indication Signal (AIS)
The test set 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.
Go back to top Go back to TOC
APS Sequence
The associated K1/K2 sequence and received K1/K2 bytes may be captured.
Event Details
RXT-3900 e-Manual D07-00-111P Rev A00