Use power monitoring to process problems on IN_PWR_LOW alarm.
Symptom
In a network consisting of the OptiX Metro 6100, five stations form a link. Station 1 and 5 are the service convergence point and configured as the OTM stations. Other stations are configured as OADM stations and each of them has two GE services with station 1 and 5 respectively. The LDG is used as the OTU and the LDG uses the PIN laser. For the timeslot, see the file in the attachment. (Note: 1:1-LDG indicates the LDG is in Slot 1 of the subrack at station 1.)
Cause Analysis
One day both 2-D:9-LDG and 3-D:9-LDG report IN_PWR_LOW alarm. The IN_PWR_LOW alarm indicates that the input power is too low and the alarm is reported through the LDG-och-1 port (WDM-side port). On the T2000, query the power of the two boards. The current input power of the 2:9-LDG-och-1 is -19.2 dBm and that of the 3:9-LDG-och-1 is -20.2 dBm, which are below the receiver sensitivity of the PIN laser (-18 dBm). Thus, the alarm occurs. Compare the queried power value with the values recorded during maintenance, and it is found that the power of each wavelength has degraded by 5-6 dB.
Analyze the services against the timeslot diagram. It is found that the routing shared by the two services is between stations 3 and 5. Thus, you can locate the problem in the section between stations 3 and 5.
Procedure
- Query the optical power of the 4:9-LDG-och-1 and compare it with the original value as recorded. You can find there is little change. Query the optical power of the 1:3-LDG-och-1 and find it is -17.5 dBm, whereas the original value is -12.4 dBm. The optical power of the 1:3-LDG-och-1 has degraded by 5.1dB, but no alarm is generated though it is below the receiver sensitivity. Thus, the failure can be located to the section specified by the routing shared by the three services; that is, the section between station 3 and station 4. In addition, query the power of the other direction, and find the power is similar to the original value as recorded in the initial maintenance. At this stage, you can determine that the problem is located in the direction where station 3 receives services from station 4. Moreover, the problem lies in the optical path shared by all wavelengths.
- Check with the maintenance personnel at station 3 and station 4 over the phone to find whether the fiber jumpers or equipment is moved. It is confirmed that the ODF and the relevant documents at station 4 are available at about 9 o'clock. Then, the maintenance personnel at station 4 check the ODF and find that the fiber responsible for transmitting the service from station 4 to station 3 is bent, which is then restored to the normal condition. At this stage, it is found that optical power is recovered.
Reference Information
- The processing of the fault occurred in the WDM equipment also should comply with the principle for processing the common failures; that is, locate the failure to a single station according to the signal flow.
- The processing of the failure occurred in the WDM equipment, however, has its unique features. In the case of one-channel 2.5 Gbit/s, regardless of the dispersion, the essential cause for the problem is the optical power. Especially when the MCA is not configured, the optical power is the primary index for us to know the network operation status. The T2000 provide a good monitoring method for us, so we must make full use of it.
- During the maintenance of WDM equipment, recording the power of each reference point of the equipment is very important. We must do well in recording the power values once the project is completed. Firstly, keep the project completion documents. Secondly, during the maintenance, though the power differs slightly at different stages, record the variation in time; if the power differs greatly, you must deal with the problems in a timely manner. In this way, you can ensure that the equipment operates with proper power. The detailed maintenance documents of the power are helpful to resolve the problem in the shortest time.
- Familiarize yourself with the equipment performance and the T2000. For example, the LDG has four pairs of optical interfaces, which are called IN1/OUT1 (WDM-side 1), IN2/OUT2 (WDM-side 2), RX1/TX1 (client-side 1), and RX2/TX2 (client-side 2). On the T2000, however, they are called LDG-och-1, LDG-och-2, LDG-och-CTL-3, and LDG-och-CTL-4, respectively.
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