1. NG Setup Failure
Example:
NGSetupFailure
Cause: misc.unspecified
Reason:
AMF rejects gNB connection.
Common Causes:
-
PLMN mismatch
-
TAC not configured in AMF
-
Unsupported gNB ID
-
AMF overload
Troubleshooting:
Verify PLMN and TAC configuration in AMF.
2. Initial UE Message Failure
Symptom:
Initial UE Message missing.
Cause:
gNB does not forward Registration Request to AMF.
Possible Reasons:
-
RRC failure
-
UE not reaching NAS layer
-
gNB configuration issue
Check sequence:
RRC Setup Complete → Initial UE Message.
3. Unknown UE NGAP ID
Example:
Error Indication
Cause: unknown-local-UE-NGAP-ID
Reason:
AMF cannot find UE context.
Common Causes:
-
UE context deleted in AMF
-
gNB restarted
-
SCTP session reset.
4. Authentication Failure
Example NAS message:
Authentication Failure
Cause: MAC failure
Possible Causes:
-
Wrong subscriber key
-
UDM/AUSF problem
-
SIM mismatch
Seen in packets:
Downlink NAS Transport → Authentication Request
Uplink NAS Transport → Authentication Failure.
5. Security Mode Failure
Example:
Security Mode Reject
Reason:
UE rejects security algorithms.
Possible Causes:
-
Ciphering mismatch
-
Integrity algorithm unsupported.
6. Initial Context Setup Failure
Example:
InitialContextSetupFailure
Cause: radioNetwork unspecified
Reason:
gNB cannot allocate resources for UE.
Possible Causes:
-
Radio resource shortage
-
QoS mismatch
-
Network slice not supported.
7. PDU Session Resource Setup Failure
Example:
PDUSessionResourceSetupFailure
Possible Causes:
-
SMF rejected session
-
UPF unreachable
-
Wrong DNN/APN configuration.
8. UE Context Release
Example:
UEContextReleaseCommand
Cause: radioConnectionWithUElost
Reason:
UE radio link lost.
Common Causes:
-
Poor signal
-
UE mobility
-
RRC failure.
9. SCTP Association Reset
Transport layer issue.
Examples:
SCTP ABORT
SCTP SHUTDOWN
Possible Causes:
-
gNB restart
-
AMF restart
-
Firewall issue.
10. Error Indication Message
Example:
ErrorIndication
Cause: protocol semantic-error
Possible Causes:
-
Vendor interoperability issue
-
Incorrect IE encoding
-
Unsupported optional fields.
Important Wireshark Filters
N2 Interface:
sctp.port == 38412
NGAP Only:
ngap
Errors:
ngap && ngap.Cause
| Failure | Impact |
|---|---|
| NG Setup Failure | gNB cannot connect to AMF |
| Initial UE Message Reject | UE cannot register |
| Authentication Failure | UE authentication fails |
| Security Mode Failure | Security negotiation fails |
| Initial Context Setup Failure | UE context not created |
| PDU Session Setup Failure | Data session fails |
| UE Context Release | Session drops |
| Handover Failure | Mobility issue |
| Paging Failure | UE unreachable |
| SCTP Failure | N2 connection down |
