Description of the problem

An OSN350 SSN4SL64 service passes through points A, B, and C. The circuit board at point C does a loopback, and a PRBS test is done on the N4SL64 circuit board at point A, but the test does not work.

Processing

First of all, according to this phenomenon in the laboratory to reproduce, found that the test does not work. After inquiring the manual of the chip SDxxxx used in SSN4 series lines, it is found that the PRBS test detection unit of this chip is detected in the direction of line transmission, so the test method of the existing network can only fail to send the PRBS test data to the line transmission side of the single board of the SSN4 line, and thus the test cannot be passed. According to the result of this analysis, loopback at site C and cross loopback at site A at the same time make the service form a closed loop, in this case the test PRBS passes.

Root Cause

The root cause of this problem is the chip SDxxxx used in the SSN4 series lines, which has a PRBS test detection unit that detects the line in the transmit direction.

Solution

Emergency recovery measures: It is necessary to do loopback at the downstream and upstream of the single board of the test PRBS to ensure that the PRBS service forms a closed loop.

Complete solution: Do loopbacks at the downstream and upstream of the single board of the test PRBS at the same time to ensure that the PRBS service forms a closed loop.

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