An incorrect VC-12 timeslot numbering scheme is used. Therefore, timeslot collision occurs when a VC-3 service is created. Hence, you need to perform the service configuration according to the selected VC-12 timeslot numbering scheme when creating a VC-12/VC-3 service.
Product

OptiX OSN 1500
Fault Type

Others
Symptom

Create VC-12 services 1 to 15 one after another in the STM-1 frame. Then, create a VC-3 service in the second VC-3 of the STM-1 frame. It is found that an alarm is generated to report the timeslot collision.
Cause Analysis

The sequential mode (ITU-T) is used as the VC-12 timeslot numbering scheme. Hence, the 15 VC-12 services occupy the second VC-3. Then, timeslot collision is reported when you create the VC-3 service in the second VC-3.
Procedure

Right-click the NE on the T2000 and select Service Configuration.
According to the service configuration and engineering planning, click Option and select ITU-T or Interleaved as the VC-12 timeslot numbering scheme.
Create the services according to the selected VC-12 timeslot numbering scheme.
Reference Information

When you create a VC-12/VC-3 service on the T2000, configure the service according to the selected VC-12 timeslot numbering scheme. The following VC-12 timeslot numbering schemes are available:
Sequential mode (ITU-T): The VC-12 timeslots that are numbered 1, 4, 7, 10, and so on belong to the first VC-3, the VC-12 timeslots that are numbered 2, 5, 8, 11, and so on belong to the second VC-3, and so on.
Interleaved mode: The VC-12 timeslots numbered 1 to 21 belong to the first VC-3, and the VC-12 timeslots numbered 22 to 43 belong to the second VC-3, and so on.