| Protocol | f1ap | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 38.473 | Spec Section | Sections 8.5.2 and 9.2.4.3 (Release 18) |
| Direction | gNB-CU -> gNB-DU initiatingMessage | Message Type | Public warning broadcast cancellation request |
| Full message name | PWS Cancel Request |
|---|---|
| Protocol | F1AP |
| Technology | 5G |
| Direction | gNB-CU -> gNB-DU initiatingMessage |
| Interface | F1-C |
| Signaling bearer / channel | Non-UE-associated F1AP signaling / SCTP-carried F1AP initiatingMessage |
| Typical trigger | The CU receives a warning withdrawal or must remove an existing warning broadcast from DU cells. |
| Main purpose | Withdraws warning broadcasts from selected DU cells or the entire DU, with either an identified warning or all warnings selected for cancellation. |
| Main specification | 3GPP TS 38.473, Sections 8.5.2 and 9.2.4.3 (Release 18) |
| Release added | Release 15 |
| Procedures where used | Emergency alert withdrawal, Removal of stale warning broadcasts, Cell-scoped public warning cleanup |
PWS Cancel Request lets the gNB-CU instruct the gNB-DU to stop an ongoing public warning broadcast over F1-C.
Withdraws warning broadcasts from selected DU cells or the entire DU, with either an identified warning or all warnings selected for cancellation.
Read three things first: the transaction, which warnings are selected, and which cells are selected.
Call flow position: The CU selects the warning identity and sends a cancellation request to the DU.
Typical state: A warning broadcast is being withdrawn.
Preconditions:
Next likely message: PWS Cancel Response
Call flow position: The CU selects cancel-all and optionally restricts the affected cells.
Preconditions:
Next likely message: PWS Cancel Response
Previous message(s): Write Replace Warning Request, Write Replace Warning Response, NGAP PWS Cancel Request, when initiated through the core network
Next message(s): PWS Cancel Response
Security context: This node-level procedure does not establish a UE security context.
-- Teaching outline, not compilable ASN.1
PWSCancelRequest
protocolIEs
TransactionID mandatory
NumberofBroadcastRequest mandatory
Broadcast-To-Be-Cancelled-List optional
Cancel-all-Warning-Messages-Indicator optional
NotificationInformation optional
Optional ASN.1 presence does not remove the procedure rule: at least one warning selector is needed.
F1AP-PDU
initiatingMessage
procedureCode: id-PWSCancel
criticality: reject
value: PWSCancelRequest
protocolIEs:
- id: id-TransactionID
value: 43
- id: id-NumberofBroadcastRequest
value: 0
- id: id-Broadcast-To-Be-Cancelled-List
value:
- nr-cgi: "00101-000000321"
- id: id-NotificationInformation
value:
messageIdentifier: "0x1100"
serialNumber: "0x0042"
| IE | Presence | Description |
|---|---|---|
Message Type | Mandatory | Identifies PWS CANCEL REQUEST through the F1AP PDU envelope. |
Transaction ID | Mandatory | Matches the cancellation request to its response. |
Number of Broadcasts Requested | Mandatory | Mandatory on the wire, but not used in this Release 18 specification version. |
Cell Broadcast To Be Cancelled List | Optional | Restricts cancellation to listed NR CGI values. Omission selects all cells of the receiving DU. |
Cancel-all Warning Messages Indicator | Optional | Selects all warnings within the cancellation area; Notification Information is then ignored. |
Notification Information | Optional | Contains Message Identifier and Serial Number for a specific warning. Needed unless cancel-all is present. |
Message TypeIdentifies PWS CANCEL REQUEST through the F1AP PDU envelope.
Presence: Mandatory
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.
Transaction IDMatches the cancellation request to its response.
Presence: Mandatory
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.
Number of Broadcasts RequestedMandatory on the wire, but not used in this Release 18 specification version.
Presence: Mandatory
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.
Cell Broadcast To Be Cancelled ListRestricts cancellation to listed NR CGI values. Omission selects all cells of the receiving DU.
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.
Cancel-all Warning Messages IndicatorSelects all warnings within the cancellation area; Notification Information is then ignored.
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.
Notification InformationContains Message Identifier and Serial Number for a specific warning. Needed unless cancel-all is present.
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.
Likely cause: Neither warning selector was supplied.
What to inspect: Notification Information and Cancel-all Warning Messages Indicator.
Next step: Build a request with the intended warning selector.
Likely cause: The cell list was omitted.
What to inspect: The encoded request and the receiving DU's served-cell inventory.
Next step: Check scope selection before issuing further cancellation requests.
Likely cause: There was no matching ongoing broadcast to stop in that cell.
What to inspect: Warning identity, prior activation, and DU broadcast state.
Next step: Reconcile the warning inventory before treating the result as a transport failure.
Uses the warning identity to select one warning.
Uses cancel-all to select every warning in the chosen DU cell scope.
The gNB-CU sends it to the gNB-DU over F1-C.
No. The DU treats that combination as a logical error.
No. It selects all cells of the receiving DU.
No. NGAP carries core-to-RAN signaling; this page describes CU-to-DU signaling.
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.