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1. For Alarm 1:
In the Synchronous Digital Hierarchy (SDH) protocol, if J0, J1, or C2 does not match, an alarm is generated. If the alarm occurs, the interface may be Down; the service is interrupted; the packets cannot be forwarded. During the interconnection with other vendors' devices, the interface is Down because the parameter does not match.
2. For Alarm 2:
LOS: If the received signals in 20 consecutive Nanosecond (ns) (± 3 ns) are "1" or "0", the signals are regarded as lost. LOS interruption is generated. When the two valid frames are received without frame loss, LOS interruption disappears.
OOF: The frame header cannot be identified for the four consecutive frames. No correct A1A2 is received.
LOF: When OOF lasts 3 ms, LOF interruption is generated. When the in-frame lasts 3 ms, LOF interruption disappears.
AIS: alarm indication signal.
RDI: remote defect indication.
When the five consecutive frames (625us) do not receive correct A1 and A2, that is, the consecutive four frames cannot identify the frame header, the receive end is asynchronous and OOF is generated. If OOF lasts 3 ms and is asynchronous, the device generates LOF. AIS signal is inserted in the local end and RDI is sent to the peer. The service is interrupted. In the LOF state, if the receive end is in the framing state over 1 ms, the device becomes normal.
3. For Alarm 3:
B1, B2, and B3: These three error codes check different positions of STM-1 frames.
B1: B1 is in the regenerator section and is used to check STM-1 frames as a whole.
B2: B2 is in the regenerator section of the SDH frame and is used to check the regenerator section and payload.
B3: B3 is in the path cost of the SDH frame and is used to check data payload.
REI: Remote error indication. It is remote alarm information sent by the receive end to the transmit end. M1 is used to transmit block errors checked by B2 of the receive end. In this manner, the transmit end learns error bits of the receive end.