OSN3500 V1R3 version, IDQ1 single board is configured, when ATM cross configuration is performed on this single board, an error message appears, the number of VC connections exceeds the limit, error code 39839, the configuration fails.

Alarm message

Processing

After checking some documents, we didn't see such a limitation, but when we checked the port properties with T2000, we found that the default maximum supported PVC VPI value of the port is 2, does it mean that only two different VPI values can be used in the default maximum supported PVC connection of a port? At present, we have already used two VPI values in the PVC connections we have configured on this port, and it is the third VPI that makes it impossible to add a PVC connection successfully. We try to modify this value, but unfortunately, it cannot be modified when there is no ATM connection on this port, and it can only be modified successfully after activating the ATM connections of the entire single board, and we modify this value to 3, and then modify it again. This value is changed to 3, and then add a new PVC connection, the operation is successful.

Root Cause

IDQ1 board supports 2048 VC connections, but we only configured 68 PVCs on this board, which should not exceed the board's limitation, so we suspect that there is also a limitation of VC connections on the ports.

Recommendations and Summary

Moreover, a port supports 2 VPI values for PVC connections by default, which is still too few, and it is very easy to set off this limitation in daily configuration, which requires us to carry out detailed planning before configuring ATM services, otherwise, we will find that we can't add a new service only after we have started the service, and then we will modify the parameters to adapt to it, which has a relatively big impact on the existing running service.