Fault Type

Bit Errors

Optical Power Abnormity

BEFFEC_EXC

 

Symptom

Station A and B form an OTM with station C functioning as an OLA in between. The BWS

1600G is used at each station and the LWF is used as the OTU board.

The LWF at station A in slot 3 keeps reports the BEFFEC_EXC alarm transiently. Query the

WDM performance of the board. It is found that there are a lot of FEC correction events (the

number of corrected bytes is larger than 100 thousand).

 

Cause ***ysis

·         

The optical power is abnormal.

·         The fiber connector is dirty or is connected improperly.

·         The dispersion is too high, or signal-to-noise ratio is too low.

 

Procedure

 

Step 1 The board reports the alarm indicating that excessive bit errors are detected. Query the optical

power of the board. The input optical power on the WDM side is -6.9 dBm, which is within the

normal range.

 

Step 2 Perform the following steps to rectify the possible fiber faults. Check the fiber jumpers and clean

the fiber connectors at stations A and B. There is no obvious change in the performance and the

alarm persists.

 

Step 3 Query the performance of other LWF boards at station A. There are FEC correction events in

the three LWF boards in slots 4-6 and the BER before FEC correction is very high.

 

Step 4 Query the optical power of all boards at station A. The input optical power on the WDM side

of every LWF board is about -7 dBm (slightly higher than -7 dBm). Query the threshold of the

input optical power at the IN interface of the board by using the T2000. The threshold is -2.0

dBm. According to the optical power adjustment principle (plus 3 minus 5), the input optical

power must be 5 dBm smaller than the receiver overload. The input optical power of the OTU

at station A is close to the threshold but not reach the value that triggers an optical power alarm.

The bit errors may be generated because the optical power is slightly high.

 

Step 5 The optical power of every board is slightly high. In this case, you can adjust the optical power

by decreasing the gain of the OAU board. Query the gain of the OAU at station A. The gain is

close to the lower limit. Decrease the gain of the OAU at station C by using the T2000. Then,

query the optical power of every LWF at station A. The input optical power at the IN interface

is about -9 dBm. Observe the performance. The number of error correction events decrease

dramatically and the LWF in slot 3 does not report the alarm any more.

 

 

One of the time consuming faults in to locate bit error generation station/node/board/port.

bad alarm of all time, even myself have suffered long hours to rectify these annoying but errors, worth reading!

bit errors aka rats in the core of fiber, too hectic to find some. please excuse the pun.

Very good read for a transmission engineer

Only copy from solution of Huawei

Although these cases can also be incorporated as an individual experience. I have faced many.

Further, you can ask any question to verify my credibility to any of the posts shared by me.