There is a STM-16 ring formed by five OSN 3500, the ring has a PP-uniform protection in the VC4 1-10 and the other 6 VC4 (11-16) are unprotected. When the customer tries to create a new VC-12 services in the unprotected time-slots between the Node A and Node C, the services show "TU_AIS" alarm.
The connection between the OSN equipment is through a DWDM network. Figure 1
"TU_AIS" alarm. When the TU_AIS alarm occurs, the services in the path are interrupted.
1. The tributary boards of the Nodes A and C show "TU_AIS" alarm.
2. There aren't any higher-level alarm.
3. The cross-connections of each involved equipment in the new unprotected VC-12 service was checked by T2000 and by Navigator and all cross-connections are created.
4. The tributary boards in the node A and C were changed but the problem coninued.
5. The Cross-conection and line boards were changed in the nodes A,B and C but the services continued with alarms.
6. As additional test new test services were proved between the node A and C but this new services continued with the same problem.
7. We proved loop back with cross-connections over the new services, however the services continued with TU_AIS alarm.
8. In order to verify the phisical connections, we did several test with the J0 Byte between the OSN equipments and the DWDM equipment and with the AIS alarm insertion in the VC4 11-16 in all nodes.
This test proved that the fibers of the line boards are logical created in a wrong direction in the nodes B and C (the logical fibers are different to the physical connections), the figure 2 shows the physical connections.
The new unprotected services show TU_AIS because the cross-connection are created to the wrong line board.
9. There are other configured services in the STM-16 link and this problems affect them as following:
a. The pass-through services that use the VC4 1-10 in the node B or C, don’t be affected by this problem, because the cross-connections are created between the line boards.
b. The add/drop services that use the VC4 1-10 are working because in a SNCP protection the cross-connection are created between the tributaruy board and the line boards, it means the cross-conection are created in esat and weas direction. However this can be a problem for the switching events.
c. The pass-through services that use the VC4 11-16 in the node B or C, don’t be affected by this problem, because the cross-connections are created between the line boards.
d. For the new add/drop unprotected services in the node B or C that use the VC4 11-16, the cross-connections aren’t created in all directions and the trail shows TU_AIS alarms by a cross-connection incorrect configuration.
As the alarm is related with the correct configuration of the service, is necessary to identify the failure point in the path:
1. View the TU_AIS alarm on the T2000 to confirm the relevant board.
2. Check whether any higher-level alarm, such as R_LOS, R_LOC, R_LOF, MS_AIS, AU_AIS, AU_LOP or HP_SLM, is detected on the T2000. If yes, take priority to clear it, and then check whether the TU_AIS alarm is cleared. If the alarm persists, go to the next step.
3. Check whether the service cross-connection configuration of the NE is correct. After modifying the incorrect configuration, check whether the TU_AIS alarm is cleared. If the alarm persists, go to the next step.
4. Replace the tributary board that reports the alarm, and then check whether the TU_AIS alarm is cleared.
5. Replace the cross-connection and timing board. The line boards can be replaced too.
Besides to check whether the service cross-connection configuration of the NE is correct, check if the logical connections are created like the physical connections.