Fault Phenomena
5.5 Troubleshooting Pointer Justifications
When an NE reports a large number of justification events about the administrative unit (AU) pointer or the tributary unit (TU) pointer, there are pointer justification faults.
Fault Phenomena
When the position of the first byte of the VC-4 in the AU-4 payload changes, the AU pointer makes a justification accordingly. The performance events related to the AU pointer justification are as follows:
l AUPJCHIGH
l AUPJCLOW
l AUPJCNEW
NOTE
The AU pointer justification is made at an upstream NE but is detected and reported at a downstream NE.
When the service is configured to be at the VC-12 level, apply the reframing process to terminate the AU pointer justification. The terminating method is to transform the AU pointer justification into the TU pointer justification. The performance events related to the TU pointer justification are as follows:
l TUPJCHIGH
l TUPJCLOW
l TUPJCNEW
NOTE
The TU pointer justification is made at the NE where the AU pointer is transformed into the TU pointer, but is detected and reported by the tributary board of the NE where services are terminated.
5 Troubleshooting
OptiX RTN 950 Maintenance Guide (U2000)
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Fault Causes
l The clock sources or the clock source levels are configured incorrectly. As a result, there are two clock sources on the same network or a timing loop occurs.
l The fiber connections are incorrect. As a result, a timing loop occurs.
l The quality of the clock source declines, the clock unit is faulty, or there are other clock-related faults.
l The tributary board is faulty (only for the TU pointer justification).
Fault Locating Methods
When there are both AU pointer justifications and TU pointer justifications on a service path, first handle the AU pointer justifications and then the TU pointer justifications.
Fault Fault Locating Method
AU pointer justification 1. Analyze and clear clock alarms.
2. Rectify the incorrect data configuration and incorrect fiber connections.
3. Change the clock configuration to locate the station whose clock is asynchronous with the entire network.
4. Replace the parts whose performance may deteriorate with new ones.
TU pointer justification 1. Analyze and clear clock alarms.
2. Rectify the incorrect data configuration and incorrect fiber connections.
3. Change the clock and service
configuration to locate the station whose clock is asynchronous with the entire network.
4. Replace the parts whose performance may deteriorate with new ones.
Troubleshooting Procedure
Figure 5-6 Procedure for troubleshooting pointer justifications
Start
Is there a clock-related alarm?
No
Yes Clear the alarm
Incorrect fiber
next step Is the fault rectified?
End
Locate the faulty board Locate the NE whose clock
is out of synchronization
Locate the faulty board Locate the NE whose clock
is out of synchronization No
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Table 5-8 Description of the procedure for troubleshooting pointer justifications Comment
No. Description
1 Pay special attention to the following alarms:
l TEMP_ALARM
l HARD_BAD
l LTI
l SYNC_C_LOS
l S1_SYN_CHANGE
l EXT_SYNC_LOS
2 Check the following points:
l Check whether there are two clock reference sources on the entire network.
l Check whether a timing loop is generated.
3 Query ECC routes to check whether the fibers are connected correctly. Check the fiber connections in the east and west directions of the NE that reports the pointer justification event.
4 The troubleshooting procedure is as follows:
1. Locate a VC-4 channel that reports an AU pointer justification event.
2. Along the service source direction of the VC-4 channel, locate the source NE of the entire VC-4 service (not the source NE of a timeslot in the VC-4).
3. Set the clock of the source NE to the free-run mode. Set the other NEs to trace the clock of the source NE along the direction of the VC-4 service.
4. Along the clock tracing direction, locate the line board that is the first to report the AU pointer justification of the VC-4 path.
The clock of the remote NE to which the line board is connected is asynchronous with the reference clock. Hence, the line board on the remote NE that receives the clock signal, the line board that sends the clock signal to the remote NE, and the clock unit of the remote NE, may be faulty.
5. Set the clock of the sink NE to the free-run mode. Set the other NEs to trace the clock of the sink NE along the direction of the VC-4 service.
6. Along the clock tracing direction, locate the line board that is the first to report the AU pointer justification of the VC-4 path.
The clock of the remote NE to which the line board is connected is asynchronous with the reference clock. Hence, the line board on the NE that receives the clock signal, the line board that sends the clock signal to the NE, and the clock unit of the NE, may be faulty.
7. Compare the results and find out the common points.
5 Replace the possibly faulty boards.
Comment
No. Description
6 The troubleshooting procedure is as follows:
1. Modify the service configuration to ensure that the NE where the clock reference source functions as the central NE and that the other NEs have the E1 services of the central NE.
2. Along the clock tracing direction, locate the NE that is the first to report the TU pointer justification event.
The clock of the NE is asynchronous with the reference clock. Hence, the line board on the NE that receives the clock signal, the line board that sends the clock signal to the NE, and the clock unit of the NE, may be faulty.
3. Modify the configuration data to ensure that all the NEs trace the clock along the other direction.
4. Along the clock tracing direction, locate the NE that is the first to report the TU pointer justification event.
The clock of the NE is asynchronous with the reference clock. Hence, the line board on the NE that receives the clock signal, the line board that sends the clock signal to the NE, and the clock unit of the NE, may be faulty.
5. Compare the results and find out the common points.
NOTE
This method is also applicable to locating an AU pointer justification event.
7 Replace the possibly faulty boards. In the case of a TU pointer justification event, check whether the line board, the clock board, and the tributary board are faulty.
Experience and Summary
On a properly synchronized network, there are few pointer justifications (less than six per day on each port). Hence, monitoring the pointer of an SDH transmission system is an effective way to check the synchronization status of the system.