Hello, everyone!
Loopback is often used in troubleshooting. This time, let's discuss how to use loopback to troubleshoot.
Generally，there are software loopbacks and hardware loopbacks, which have the following advantages and disadvantages:
A hardware loopback is performed on a physical port (optical port) using an optical fiber. Compared with the software loopback, the hardware loopback is more reliable. The hardware loopback, however, requires on-site operations. In addition, a receive optical power overload must be avoided when performing a hardware loopback.
Compared with the hardware loopback, the software loopback is simpler but cannot locate a fault as accurately. For example, during a single station test, if a software inloop is performed on an optical port and the service is normal, the line board may not necessarily be normal. However, if a selfloop is performed on the same optical port using a pigtail and the service is normal, the line board is normal.
What we need to pay attention to is:
1. When performing a loopback on the optical path of the multiplex section, ensure that the OSNR and dispersion meet the OTU requirements.
2. This method affects service quality. Therefore, it is generally used in deployment commissioning or fault location in situations where services have been interrupted.
3. If the protection scheme has been configured, loopback is not recommended. Otherwise, protection switching may fail. If loopback is required, lock the protected services on the current channel before performing the loopback, and unlock the services after the loopback is completed.
4. The loopback method is applicable when the approximate range of the fault is known. The fault is located by applying the loopback method on a section by section basis. This method clears board and line faults.
5. If the system is capable of automatically releasing a loopback, the automatic loopback release period can be changed or entirely disabled on the U2000. By default, the automatic loopback release period is five minutes.
Take an example
In the following figure, the client-side of the OTU at station A reports a R_LOS alarm whereas the WDM side at station A reports no alarm. The WDM side and client-side of the OTU board at station B report no alarms whereas the client equipment at station B reports a R_LOF alarm.
Perform an in-loop on the client-side of the OTU board at station A as shown in figure
If the alarms at both stations A and B are cleared, the OTU board at station A is receiving no signal from the client equipment at station A. The fault is occurring on the client equipment at station A or the optical fiber from the client equipment at station A to the OTU board at station A.
If the alarms at stations A and B persist, the fault is occurring on the OTU board at station A.
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