PWS Failure Indication is the NGAP warning message sent by the NG-RAN node to the AMF when public warning broadcast delivery fails or cannot be maintained.
Message Fact Sheet
Protocol
ngap
Network
5g
Spec
3GPP TS 38.413
Spec Section
Warning Message Transmission Messages and PWS Failure Indication
PWS Failure Indication is the NGAP warning message sent by the NG-RAN node to the AMF when public warning broadcast delivery fails or cannot be maintained.
Reports public warning delivery failure, identifies affected cells or areas, helps AMF track warning broadcast status, supports public safety warning reliability, and enables retry or corrective action.
Why this message matters
PWS Failure Indication is the gNB telling the AMF that a public warning broadcast failed in specific cells. Start troubleshooting with PWS Failed Cell List.
Where this message appears in the call flow
PWS Failure Indication
PWS Failure Indication reports that warning broadcast failed or could not be maintained.
Call flow position: NG-RAN sends this non-UE-associated initiatingMessage when warning broadcast delivery fails or cannot be maintained.
Typical state: AMF learns which cells or areas experienced warning delivery failure.
Preconditions:
Warning broadcast was requested or active.
PWS Failed Cell List identifies affected cells.
Optional area or node context is decoded when present.
Next likely message: AMF retry, update, cancel, or operational escalation
Failed cell analysis
PWS Failed Cell List is the primary field for warning broadcast failure troubleshooting.
Call flow position: PWS Failed Cell List is the primary troubleshooting field.
Typical state: Engineers distinguish partial failure from complete warning-area failure.
Preconditions:
Failed cells are mapped to the intended warning area.
Original Write Replace Warning Request and response are available.
Next likely message: Failed cell investigation
Failure versus restart/cancel
Failure, restart recovery, warning request, and cancellation are separate warning-procedure states.
Transport / encapsulation: NGAP over SCTP/IP between NG-RAN and AMF
Security context: The message reports failed public warning delivery scope and may drive emergency warning retry, escalation, or corrective action. It should be correlated with active warning state, cancellation state, and restart events.
Message Structure Overview
PWS Failure Indication is an NG-RAN-to-AMF non-UE-associated initiatingMessage.
PWS Failed Cell List is the mandatory troubleshooting payload.
Optional Global RAN Node ID identifies the reporting node.
Optional TAI and Emergency Area ID lists identify broader failure scope.
The message can occur after a successful Write Replace Warning Response if later delivery fails.
ASN.1 for 5G NGAP - PWS Failure Indication
PWSFailureIndication ::= SEQUENCE {
protocolIEs ProtocolIE-Container { {PWSFailureIndication-IEs} },
...
}
PWSFailureIndication-IEs NGAP-PROTOCOL-IES ::= {
{ ID id-PWSFailedCellList CRITICALITY ignore TYPE PWSFailedCellList PRESENCE mandatory } |
{ ID id-GlobalRANNodeID CRITICALITY ignore TYPE GlobalRANNodeID PRESENCE optional } |
{ ID id-TAIListForPWSFailure CRITICALITY ignore TYPE TAIListForPWSFailure PRESENCE optional } |
{ ID id-EmergencyAreaIDListForPWSFailure CRITICALITY ignore TYPE EmergencyAreaIDListForPWSFailure PRESENCE optional },
...
}
How to read this ASN.1
Decode PWS Failed Cell List first. Then inspect reporting node, tracking area, and emergency area context to understand failure scope.
Treat this as a teaching example based on the expected message structure, not as a captured network trace.
PWS Failed Cell List is the first field to inspect.
Correlate failed cells with the original warning area and any restart or cancel messages.
Important Information Elements
IE
Required
Description
Message Type
Yes
Identifies the NGAP PDU as PWS FAILURE INDICATION.
PWS Failed Cell List
Yes
Mandatory list of cells where warning broadcast failed or could not be maintained.
Global RAN Node ID
Optional
Optional identity of the NG-RAN node reporting the failure.
TAI List for PWS Failure
Optional
Optional tracking areas affected by the warning delivery failure.
Emergency Area ID List for PWS Failure
Optional
Optional emergency warning areas affected by the warning delivery failure.
Detailed field explanation
Message Type
Identifies the NGAP PDU as PWS FAILURE INDICATION.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
PWS Failed Cell List
Mandatory list of cells where warning broadcast failed or could not be maintained.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Global RAN Node ID
Optional identity of the NG-RAN node reporting the failure.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
TAI List for PWS Failure
Optional tracking areas affected by the warning delivery failure.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Emergency Area ID List for PWS Failure
Optional emergency warning areas affected by the warning delivery failure.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Can PWS Failure Indication occur after Write Replace Warning Response?
Yes. A response can indicate request handling, while later PWS Failure Indication reports delivery failure in one or more cells.
How do you troubleshoot public warning failure in NGAP?
Decode PWS Failed Cell List, map affected cells and areas, correlate with Write Replace Warning Request/Response, check for PWS Cancel and PWS Restart, and verify RAN resources and topology.
Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.
