Description of the problem

As shown in the figure, the SNCP protection group was set up at the OSN3500 site, and when the fiber pull test was performed between the ABs, the SD inversion occurred at the SNCP at the OSN3500 site, but the delay time didn't work, and the meter observed that the inversion time was less than the delay event

Processing

First of all, after doing tests in the current network, it is found that when the inversion is triggered by turning off the laser, the delay time is working at this time, i.e., when the SNCP will not be inverted, and the main and backup of the MSPs are disconnected, the SNCP will be inverted at this time, and the time of inversion will be greater than the set delay time.

The lab simulates the existing network test environment and is able to reproduce the existing network problem, which is characterized by the fact that when there is SD in the optical path, the SNCP inversion delay time is not in effect. The lab observed that at this point the service would be interrupted twice, with each interruption being no greater than 50ms.

After analyzing the code as well as doing debugging software, it was found that the root cause of the problem is: line board detection B3_SD/B3_EXC is refreshed by a task with a period of 1 second, if the set SNCP delay time is less than 1 second, at this time, in the 1-second inspection cycle, B3_SD/B3_EXC are present, that is, even if the real B3_SD/B3_EXC is only generated for 10ms, as long as the presence of this BER is detected, the duration of this BER in the software is 1 second, and when the delay time is up, the software still thinks that this BER still exists, and therefore triggers an SNCP inversion. This inversion is the reason for the second inversion observed in the laboratory

Root Cause

The root cause of this problem is that the cycle time for the line veneer to monitor the error code is 1 second, and when a momentary (e.g., a few tens of milliseconds) error alarm is generated, the duration of this error code in the software is still 1 second, and is therefore greater than the delay time, resulting in multiple inversions.

Solution

Emergency recovery measures: Set the delay time to 1 second or more, and it is recommended to set it to 1200ms.

Complete solution measure: None

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