How to Troubleshoot the Pointer Justification on Huawei OptiX OSN 2500?

A pointer justification event means that some NEs are not completely synchronized in Huawei SDH
network equipment. If only a pointer justification event occurs, the services are not affected. To enhance
the transmission network stability, however, you need to find out the causes and eliminate the
pointer justification event.

Mechanism of Pointer Justification
Pointer justifications occur when the clocks between the NEs are not fully synchronized.
In an SDH network, there are two kinds of pointers: administrative unit pointer (AU-PTR) and
tributary unit pointer (TU-PTR). There are two corresponding pointer justifications, AU pointer
justification and TU pointer justification. The generation mechanism of these two kinds of
pointer justification is mostly the same. For details, see Chapter 1 "Generation of Alarm and
Performance" of Huawei OptiX OSN 2500 Intelligent Optical Transmission System Alarms and

Performance Events Reference.

Generation Mechanism of AU Pointer Justification
the E1 service between NE1 and NE6 passes through the intermediate NEs at
the VC-4 level. NE1 is the clock source, and the other NEs trace the clock signal of NE1
westwards. If the clocks of NEs 2 and 3 are not synchronous, the east optical board of NE2 and
the west optical board of NE3 generate the AU pointer justifications. These justifications may
cause the west optical boards of NEs 1, 4, 5 and 6 to generate pointer justifications.
If the clock of NE2 runs faster than that of NE3, the east optical board of NE2 executes the
AU positive pointer justification. At the same time, the west optical board of NE3 executes
the AU negative pointer justification.
If the clock of NE2 runs slower than that of NE3, the east optical board of NE2 executes
the AU negative pointer justification. At the same time, the west optical board of NE3

executes the AU positive pointer justification.

Detection Report of Pointer Justification
The location where AU pointers are generated and reported is different from that of TU pointers.
When a local station generates an AU pointer justification, it neither detect nor report the AU
pointer justification. Instead, this station transmits the pointer justification information to the
remote station through the H1 and H2 bytes. The remote station will report the event of the AU
pointer justification by interpreting the H1 and H2 bytes. Therefore, in remote detection mode,
if the remote station reports the AU pointer justification event, it means that the pointer

justification is generated in the local station.
Fault Locating Flow
The clock out-of-synchronization is the primary cause of pointer justification. Locate faults
mainly by handling problems related to the clocks. The fault should be located based on the
service direction, clock tracing direction, detection report location of pointer justification and

the generation location of pointer justification.

a: The first station refers to the station that first reports the pointer justification in the service direction, which is the same as the clock direction, that is, in the clock tracing direction.

b: The first station has no AU pointer justification, that is, it only has the TU pointer justification. You should handle the problem of TU pointer justification.