The following table lists the unsolicited events returned by NbUP filters:
| Event | Description |
| MSPEVN_NBUP_INIT | Indicates the completion of Initialization phase. Could be positive acknowledgement (ACK), negative acknowledgement (NACK), or Timeout. |
| MSPEVN_NBUP_ERROR | Indicates an error condition during the session. |
The following table summarizes the possible reason codes in MSPEVN_NBUP_INIT event:
| Reason code | Description |
| NBUP_INIT_SUCCESS | SUCCESS |
NBUP_INIT_TIMEOUT |
Timeout waiting for INIT message. |
| NBUP_INIT_ACK_TIMEOUT | Timeout waiting for acknowledgement |
| NBUP_INIT_NACK | Negative acknowledgement received. |
| Reason code | Description |
| NBUP_ERROR_CRC_HEADER | CRC error of frame header |
| NBUP_ERROR_CRC_PAYLOAD | CRC error of frame payload |
| NBUP_ERROR_UNEXP_FRAME_NB | Unexpected frame number |
| NBUP_ERROR_FRAME_LOSS | Frame loss |
| NBUP_ERROR_UNKNOWN_PDU | PDU type unknown |
| NBUP_ERROR_UNKNOWN_PROC | Unknown procedure |
| NBUP_ERROR_UNKNOWN_RSV | Unknown reserved value |
| NBUP_ERROR_UNKNOWN_FIELD | Unknown field |
| NBUP_ERROR_FRAMME_TOO_SHORT | Frame too short |
| NBUP_ERROR_MISSING_FIELD | Missing fields |
| NBUP_ERROR_UNEXP_PDU | Unexpected PDU type |
| NBUP_ERROR_UNEXP_PROC | Unexpected procedure |
| NBUP_ERROR_UNEXP_RFCI | Unexpected RFCI |
| NBUP_ERROR_UNEXP_VALUE | Unexpected value |
| NBUP_ERROR_INIT_FAILURE | Initialization failure |
| NBUP_ERROR_INIT_NET_FAILURE | Initialization failure (network error, timer expiry) |
| NBUP_ERROR_INIT_NACK_FAILURE | Initialization failure (IuUP function error, repeated negative acknowledgement) |
| NBUP_ERROR_RATE_CTRL_FAILURE | Rate control failure |
| NBUP_ERROR_EVENT_FAILURE | Error event failure |
| NBUP_ERROR_TIME_ALIGNMENT_NOT_SUPP | Time Alignment not supported |
| NBUP_ERROR_TIME_ALIGNMENT_NOT_POSS | Requested Time Alignment not possible |
| NBUP_ERROR_MODE_VERSION_NOT_SUPP | IuUP Mode version not supported |