Causes of an R_LOS alarm

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Client-side cause 1: On the optical connector of the local board, the pigtail is not connected, or is loosely or incorrectly connected.
Client-side cause 2: The line attenuation is too large, or a fiber cut occurs on the line.
Client-side cause 3: The board that reports the alarm is faulty.
Client-side cause 4: If the board reporting the alarm is a 40G or 100G board, at least one wavelength has been missing from the receive end of the board.
WDM-side cause 1: On the optical connector of the local board, the pigtail is not connected, or is loosely or incorrectly connected.
WDM-side cause 2: The line attenuation is too large, or a fiber cut occurs on the line.
WDM-side cause 3: The board laser at the peer site is turned off.
WDM-side cause 4: A fault occurs on the transmit module of the board at the peer site or on the receive module of the board at the local site.

Other related questions:
Cause for the R_LOS alarm during normal light receiving of the optical module on the LWX2 board
1. When an optical meter is used to measure the receive optical power of the optical module, the receive optical power is normal. 2. After the related optical power is replaced, the alarm persists. 3. When no scrambled optical signal is received on the client side, the light is white if light is forcibly emitted on the WDM side. When the WDM side does not receive any optical signal scrambled by the peer end, the light is also white if light is forcibly emitted on the client side. Based on the alarm detection mechanism, no valid information can be abstracted from white light. Therefore, an R_LOS alarm is reported. 4. When the client-side access rate of point A is changed to 622 Mbit/s and optical signals of SDH devices at the STM-4 rate level are received, the client-side R_LOS alarm is cleared on point A and the corresponding WDM-side R_LOS alarm on point B is cleared. When a hardware loopback is performed on the client side of point B, both the client-side R_LOS alarm on point B and the WDM-side R_LOS alarm on point A are cleared and the optical module fault is removed.

Differences of the MUT_LOS and R_LOS alarms on OA boards of WDM devices
Question: On Huawei WDM devices, why some OA boards report the R_LOS alarm whereas some OA boards report the MUT_LOS alarm when they do not receive any light or the receive optical power is excessively low? Analysis: None Answer: When the OA boards (such as WPA, WBA, and WLA) on 320G devices do not receive any optical signals, the R_LOS alarm is reported. When the OA boards (such as OPU, OBU, and OAU) on 1600G, 800G, and 400G devices do not receive any optical signals, the MUT_LOS alarm is reported. Suggestion and conclusion: The R_LOS alarm is used to indicate the loss of input optical signals on a single wavelength of a board such as OTU. The MUT_LOS alarm is used to indicate the loss of multiplexed optical signals on a board such as M40, D40, OAU, OBU, or OPU. It is inaccurate that the R_LOS alarm is reported when OA boards do not receive any optical signals. Therefore, the R_LOS alarm is canceled for new OA boards. When developing new 1600G, 800G, and 400G WDM systems, Huawei adjusts the alarm that is reported when OA boards do not receive any optical signals. To be specific, the OA boards report the MUT_LOS alarm when receiving no optical signals.

Causes for the issue that services are still normal at the client-side port on an L4G board where an R_LOS alarm is reported
As to a traditional SDH device, if an optical port reports an R_LOS alarm, the device will check all 1s in the payload of the channel, resulting in service interruptions. Why services of the port are still normal when an L4G board reports an R_LOS alarm on the client side? There are two causes: 1. The first cause is related to OTN principles. When an OTU board detects an R_LOS alarm on the client-side port, the device will not check all 1s in information payload. Instead, it will insert an SF event into its overhead. When the opposite end detects the SF event, the CLIENT_SF indication alarm will be reported. Although the OTU board reports the R_LOS alarm on the client side, the device will still encapsulate the weak signals received at the port. 2. Some boards can still receive valid information even when R_LOS alarms are reported on the client side. The L4G boards from different manufacturing batches use different chips, which have different sensitivity values. For some of them, although optical signal is lower than the preset R_LOS threshold, the received signals are still processed normally due to good quality of the chips.

Cause for the BEFFEC_EXC alarm
The possible causes of the BEFFEC_EXC alarm are as follows: 1. A fault occurs on an inter-site fiber or intra-site multiplexing link. 2. The signals are severely attenuated during line transmission. 3. The external environment is abnormal.

POWER_DIFF_OVER alarm cause
1. Optical signals have too large attenuation during the transmission, or an optical attenuator with high attenuation is added to the local board. As a result, the optical power of the active optical signals at the receive end greatly differs from that of the standby optical signals. 2. The transmit optical power of the active optical signals at the peer site greatly differs from that of the standby optical signals. 3. The detection circuit of the local board is faulty.

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