Problem description

A, B two sites using OSN3500 equipment for long-distance transmission, using SSN4SL64 + SSN2BPA configuration, a day, between the two points of the fiber-optic cable outage, after line testing, the interruption of the fiber-optic cable by a core, that is, the B received A direction of the fiber optic breaks, but at this time, the network management response, A, B, between interconnecting the SL64 single-board are reported to the R_LOS alarms, the line will be the core of the fiber-optic cable! After repair, both ends of the optical alarms disappear. After the line is restored, turn off the A send B direction laser simulation fiber break a core, found that A, B line board at the same time reported R_LOS alarm.

Alarm information

r_los, out_pwr_abn, in_pwr_abn

Processing

1, turn off the A send B direction laser, A, B circuit boards are reported R_LOS alarm, fiber optic cable fusion error, there will not be two places to report R_LOS alarm, to rule out the possibility of fiber cable fusion error;

2, query the circuit board laser automatic shutdown function, the circuit board does not support the function;

3, analyze the signal flow

A->B direction signal flow is A:SL64->BPA:BA->B:BPA:PA->SL64;

B->A direction signal flow is B:SL64->BPA:BA->A:BPA:PA->SL64.

4, again the network management alarms will be analyzed, issue in A after the laser is turned off, point ABPA single board BA and PA module are reported IN_PWR_ABN alarm, point B BPA single board PA module reported IN_PWR_ABN alarm, BA module reported OUT_PWR_ABN alarm. From the alarms, it can be seen that the R_LOS alarm reported on the SL64 single-board at point A is caused by the BA module at point B transmitting abnormally.

5. Why does the BA module at point B report the OUT_PWR_ABN alarm? Checking the characteristics of N2BPA, the difference between N2BPA single board and N1BPA is that N1BPA has twoEDFA modules, and N2BPA has only oneEDFA module, both of which support automatic laser shutdown and are enabled by default. For N2BPA, there is only one EDFA module, which causes the laser to turn off when there is no optical signal input to either IN1 and IN2 ports. In other words, when the PA module at point B receives no light, it will turn off the laser of the BA module, resulting in the circuit board at point A receiving no light.

Root cause

1. Fiber and cable fusion welding error;

2、The automatic shutdown function of the circuit board laser is turned on;

Recommendations and Summary

OSN3500 SSN2BPA has only 1EDFA module. When the laser auto shutdown function is turned on, note that when there is no optical signal input from either IN1 and IN2 ports, it will cause the laser to turn off.