Problem Description:
A bank Customer report that there are CRC frame in Switch S7700 (connect to DWDM 1800), but the CRC do not increase all the time, Customer replaced trail fiber and Optical module, but the problem couldn’t be solved.
CRC error received in Switch (D side):
CRC ERROR transmitted in 1800 (D side):
Topology:
Troubleshooting process:
1. The optical module and fiber trail in D site has been replaced but problem is not solved, so faulty should not be on site D (including Switch and 1800).
2. Check DWDM performance, the error after FEC in the direction from M to D is 0, the DWDM channel quality is very good. Problem is not found till now.
3. Discuss with R&D expert, DWDM can check CRC but it will transmits the CRC error frames instead of dropping them, so the CRC error frames may come from site M.
4. All the CRC counter is set to 0, after one day time, the result will be clear that where are the CRC frames produced.
5. After one day, 11 CRC frames received in Switch(D site)
Check DWDM side:
D side transmitted 10949 bytes bad packets to Switch:
In M side, DWDM received 10949 bad bytes from Switch:
So the counter as bellow picture. It is easy to confirm the problem between DWDM and Switch in M site produce the CRC frame.
Solution:
Replace the optical module and fiber between DWDM and Switch in M site.
What do we learn from the case?
In OTN equipment, bit transparently transmitted mode can check CRC too, but even if CRC frame is found, OTN will continue to transmit instead of drop it. So in this mode, we can use the CRC counter function to help to do troubleshooting where produce CRC frames.
