Problem description

1, Networking:N4SF64 --- N2BPA(BOUT)------ line -------RPC02 --- N2DCU1(60KM)--- N2BPA(POUT)--- N2DCU2(80KM)----N4SF64

2. N4SF64 is configured with Ue-64.2c, DCU is configured with N2DCU, N1DCU1 is 60KM, N2DCU2 is 80KM, BPA is configured with N2BPA, and the line length is 160KM.
3. Customers' feedback is that N2BPA often flashes the IN_PWR_LOW alarm, and the SF64 veneer receives light -9.5, and receives light normally.

Alarm information

Flashing IN_PWR_LOW alarm.

Processing

1, in the field test RPC02 SYS port luminous for -22, N2DCU1 insertion loss maximum value of 3DB, can be calculated that the normal input of N2BPA PIN port -25, field test N2BPA PIN port receiving light -36, N2DCU1 actual loss of 14DB, initially positioned as a failure of the DCU module to replace a piece of DCU, the insertion loss of 13, suspect that the replacement DCU has a fault, the replacement DCU is suspected of having a fault, the DCU is a failure. Replacement of the DCU is faulty, there is an 80KM N2DCU2 between POUT and SF64, test POUT output is -7, after N2DCU2, the output is -9.5, the insertion loss is 2.6DB, normal, the N2DCU2 and N2DCU1 position, N2DCU2 insertion loss is 14.3DB, N2DCU1 insertion loss is 2.4DB, normal. N2DCU2 is 14.3DB and N2DCU1 is 2.4DB.
2、 Adjust N2DCU1 to POUT of N2BPA, after adjusting the network: N4SF64 --- N2BPA(BOUT)------ line -------RPC02 --- N2BPA(POUT) --- N2DCU1(60KM)---- N2DCU2(80KM)----N4SF64, after adjusting the test RPC02 SYS port output is -24, BPA PIN input is -24, POUT output is 1, after two DCU output is -5, the output is normal, observe for a period of time, the work is normal, and there is no more flashing IN_PWR_LOW alarm.

Root cause

The operating wavelength of the chirp grating of the DCU board used in SDH is 1550.12nm, and the center wavelength of the SF64 single board is also 1550.12nm, but after pumping the light for the broad-spectrum RPC02 (1529-1561) backward Raman amplifier, noise light is generated, and the DCU is placed after the RPC, which filters out the noise light, so the insertion loss of the DCU is particularly large, resulting in the BPA's PIN port receiving light. The PIN port of the BPA receives relatively weak light, so the flash report IN_PWR_LOW.

Solution

Connect the BPA after the RPC, and then connect the DCU veneer after the BPA.

Suggestion and Summary

To deal with board failure type problems, you can use the replacement method and the segment-by-segment test method.