There is a PP-ring consist of four elements NE1-NE2-NE3-NE4. NE1 and NE2 are OSN2500, NE3 and NE4 are Metro 1000. When the fiber between NE3 and NE4 was cut NE4 logged of from T2000. Although it should have taken ECC from NE1.
First of all disabled ECC for all unused ports of SLT1 boards. Then disabled all D4-D12 channels because on this network they are not used. Finally only 4 ECC channels were occupied on NE1 element so it was possible to enable ECC for SLD4 board. After this NE4 logged in to T2000 and the problem was solved.
First of all locally connected to NE4 and checked if the laser on line board are opened and ECC channel is enabled on problem element NE4. It was normal. Laser status is Open and ECC channel is Enabled.
After this checked configuration on adjacent elements NE1 and NE3. NE1 ECC channels were Enabled but status was Obtaining Failed. OSN2500 support 20 ECC channels. But NE1 had two SLT1 boards which occupied together more that 20. So when SLT1 boards were inserted in the subrack ECC for all ports automatically enabled and for SLD4 board which was installed later there was no available ECC channels left.
If you have multiport board such as SLT1 and so on it’s better to disable ECC for all unused port in order not to waste ECC channel resources.