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Functional
Overview
ST112 SONET Transmission Test Set
2–11
VT Path Alarms
Figure 2–7 Receiver Status Indicators
The Virtual Tributary (VT) Path is a logical connection between the point of frame origin and the
point of destination. The structure is designed for the transport and switching of DS1 sub-
payloads. These points can be further defined as the point where the frame of a specified rate
(OC-12 or OC-3) is assembled and the point where the frame of that same rate is disassembles.
The Test Set has four VT Path LED indicators (Figure 2–7), as follows:
•
The AIS (Alarm Indication Signal) indicates an upstream VT1.5 path failure in the monitored
direction. The VT1.5 may travel across multiple STS-n or OC-n transmission facilities and a
failure in any one of them will cause a VT path AIS at all of the downstream points.
•
The RDI (Remote Defect Indicator) indicates a VT1.5 path failure in the other direction
(unmonitored direction). In other words the PTE receiving the other direction of the
monitored VT1.5 has entered a failure state or is receiving a line AIS.
•
The FEBE (Far End Block Error) indicates VT1.5 path bit errors in the other direction (i.e.
the unmonitored direction). In other words the PTE receiving the other direction of the
monitored VT1.5 has detected one or more path BIP-2 code violation.
•
The BIP-2 LED indicates that VT1.5 path code violations were detected indicating an error
condition in the monitored VT path between the monitor point and the upstream PTE.
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