| Protocol | f1ap | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 38.473 | Spec Section | Sections 8.5.3 and 9.2.4.5 (Release 18) |
| Direction | gNB-DU -> gNB-CU initiatingMessage | Message Type | Public warning restart and reload-availability notification |
| Full message name | PWS Restart Indication |
|---|---|
| Protocol | F1AP |
| Technology | 5G |
| Direction | gNB-DU -> gNB-CU initiatingMessage |
| Interface | F1-C |
| Signaling bearer / channel | Non-UE-associated F1AP signaling / SCTP-carried F1AP initiatingMessage |
| Typical trigger | DU-side PWS recovery or availability changes require the CU to reassess whether warning information needs reloading. |
| Main purpose | Identifies the DU cells for which public warning information can be reloaded if required, allowing the CU to coordinate warning-state recovery. |
| Main specification | 3GPP TS 38.473, Sections 8.5.3 and 9.2.4.5 (Release 18) |
| Release added | Release 15 |
| Procedures where used | DU PWS recovery coordination, Warning information reload assessment, Cell inventory reconciliation during recovery |
PWS Restart Indication informs the gNB-CU that some or all gNB-DU cells are available for PWS information reloading from the CBC if needed.
Identifies the DU cells for which public warning information can be reloaded if required, allowing the CU to coordinate warning-state recovery.
Read this as a cell availability notification for possible PWS reloading. It is not a confirmation that alerts are broadcasting again.
Call flow position: The DU reports the cells available for warning-information reloading.
Typical state: The CU evaluates the reported cell scope against current warning requirements.
Preconditions:
Next likely message: CU assessment, followed by warning delivery only if needed
Call flow position: The indication provides cell scope for recovery coordination rather than carrying warning content.
Preconditions:
Next likely message: A separate Write Replace Warning procedure when appropriate
Previous message(s): DU or cell recovery, depending on implementation, Earlier warning broadcast configuration, if any
Next message(s): CU assessment of warning reload requirements, Write Replace Warning Request, if warning reloading is required
Security context: This node-level notification does not establish a UE security context.
-- Teaching outline, not compilable ASN.1
PWSRestartIndication
protocolIEs
TransactionID mandatory
NR-CGI-List-For-Restart-List mandatory
item (1..512)
NRCGI mandatory
The procedure's envelope criticality is ignore; both mandatory protocol IEs have reject criticality. These apply at different levels.
F1AP-PDU
initiatingMessage
procedureCode: id-PWSRestartIndication
criticality: ignore
value: PWSRestartIndication
protocolIEs:
- id: id-TransactionID
criticality: reject
value: 44
- id: id-NR-CGI-List-For-Restart-List
criticality: reject
value:
- nr-cgi: "00101-000000321"
- nr-cgi: "00101-000000322"
| IE | Presence | Description |
|---|---|---|
Message Type | Mandatory | Identifies PWS RESTART INDICATION through the F1AP PDU envelope. |
Transaction ID | Mandatory | Identifies this F1AP procedure instance; its presence does not imply a request-response exchange. |
NR CGI List for Restart List | Mandatory | Mandatory list of reported DU cells. Each item contains a mandatory NR CGI; Release 18 permits 1 to 512 items. |
Message TypeIdentifies PWS RESTART INDICATION 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 IDIdentifies this F1AP procedure instance; its presence does not imply a request-response exchange.
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.
NR CGI List for Restart ListMandatory list of reported DU cells. Each item contains a mandatory NR CGI; Release 18 permits 1 to 512 items.
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.
Likely cause: This is normal for this Class 2 procedure.
What to inspect: CU processing logs and any separate warning-reload activity.
Next step: Evaluate handling and recovery state rather than searching for a Restart Response message.
Likely cause: The cell may not yet be available, may belong to another DU, or may be outside this report's scope.
What to inspect: NR CGI mapping, served-cell configuration, and cell recovery logs.
Next step: Reconcile the reported cells with the DU's current cell inventory.
Likely cause: Reload coordination, warning validity, or subsequent broadcast configuration may need investigation.
What to inspect: CU warning inventory, upstream recovery handling, and any new Write Replace Warning Request and Response.
Next step: Determine whether a valid warning required reloading, then locate the missing recovery step.
Restart reports cells available for possible reloading; Failure reports a failure of ongoing PWS operation.
The warning response answers a CU broadcast request. Restart Indication is initiated independently by the DU.
Cancellation reporting concerns stopping warnings, while restart reporting concerns possible reloading.
The gNB-DU sends it to the gNB-CU over F1-C.
No. It is a Class 2 notification procedure, even though Transaction ID is mandatory.
No. The list is mandatory and must contain at least one NR CGI item.
No. Verify any required reload procedure and actual DU broadcast state separately.
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.