1

The Cell Broadcast Center (CBC) creates and sends a NonUeN2InfoSubscribe to the AMF to be notified by the NG-RANs for the UE coverage of warning messages sent. The message type is the subscription parameter. The Cell Broadcase Entity (CBE) cannot subscribe a subset of warning messages.

2

The AMF creates a subscription and returns the location of the subscription to the CBE. The CBCF uses this location if it needs to modify or cancel the subscription.

3

The CBCF creates a Write Replace Warning Request NG-RAN message containing the warning message to broadcast. The message contains the following:

• Message Identifier

• Serial Number

• List of NG-RAN TAIs

• Warning Area List NG-RAN

• CWM Indicator

• Send Write-Replace-Warning-Indication

• Global RAN Node ID

• Warning Area Coordinates

This becomes a binary part to a Non-UE Message Transfer request to the AMF. The CBCF also optionally sends a list of TAI or a list of gNBs to AMF that need to receive this message.

4

The AMF responds to the CBCF that sending of warning messages to the gNodeB has started.

5

The AMF determines the set of gNB that need the message to send. This could be a list of gNB (if the CBCF sends the list), all gNB in a list of TAI, or all the gNB that are connected to the AMF. The AMF doesn't interpret the binary information that is part of the request. The AMF then sends a Write Replace warning request to the gNB.

6

The gNB responds to the warning message after broadcasting it.

7

If the CBCF has registered for notifications, the AMF notifies the CBCF. Each message that is sent by the gNB becomes an individual notification, as multiple binary payloads are not allowed in a single message.

8

The CBCF responds to the notification from the AMF.

1

The peer node sends a subscription request to the AMF, which reaches the REST-EP.

This message is either a PWS-BCAL (Broadcast Completed Area List or Broadcast Canceled Area List) or PWS-RF (Restart Indication or Failure Indication).

2

The REST-EP forwards this message to the AMF service.

3

The AMF service saves the subscription to the database and sends a success response to REST-EP. The saved subscription contains the URI of the remote node and the parameters for the subscriptions. The AMF creates a unique location URI for this subscription and includes it in the response.

4

The REST-EP responds with a 201 message to the peer node.

5

The AMF service forwards this information to the NGAP-EP.

1

The peer node sends a NonUEN2MsgeTransferRequest to the AMF. The REST-EP receives this request and forwards the message to the AMF service.

2

AMF does the following while handling the warning messages (these messages may contain filters, for example, gNB or TAIs that must match):

• On receiving the warning message, AMF service checks for protocol errors and returns error response, if there is any.

• If the warning message contains filters, the AMF forwards the message to all NG-RANS that match the filters.

• If the warning message doesn’t contain filters, the AMF forwards the message to all NG-RANs connected to this AMF.

• If the warning message contains filters but no matching NG-RANs, the AMF doesn’t send any message.

3

The AMF sends NonUEN2MsgeTransferResponce to the REST-EP.

• The AMF saves PWS messages to obtain correlation in responses, if the CBCF requests the responses to be send.

4

The REST-EP sends the response to the peer that sent the request.

5

The AMF service forwards the NonUEN2MsgeTransferRequest to the NGAP-EP. The NGAP-EP uses the parameters of the request to find the list of gNodeB to send these messages.

6

The NGAP-EP forwards the message to gNB with the following scenarios:

• The NGAP copies the N2 payload without any changes and forwards it to the gNB, when the message has the N2InformationClass set to PWS.

• The AMF performs the following actions, when the sendRanResp field in PWS information is set to true.

  • Saves the msgIdentifier and the serial number of the message.

  • Saves the notification control block for PWS information.

1

The gNB sends a Write Replace Warning Response or PWS Cancel Response to NGAP-EP.

2

The NGAP-EP generates a callback with n2InfoClass set to PWS-BCAL with the following conditions.

• Subscription for notification for this event is available.

• Serial number corresponds to a request originally send with sendRanResponse as True.

3

If the gNB sends a PWS Restart Indicator or a PWS Failure Indication, it reaches the NGAP-EP.

4

If there’s a subscription for notification of the PWS events, the NGAP-EP generates a callback with n2InfoClass set to PWS-RF.

5

The AMF service forwards the onN2InfoNotifyRequest to REST-EP.

6

The REST-EP sends the message to the peer node.

7

The peer node responds with a 204 OK.

8

The REST-EP forwards the onN2InfoNotifyResponse to the AMF.

1

The peer node sends a Delete message to the AMF with the ID assigned during the subscription process .

2

The REST-EP forwards the request to the AMF service.

3

The AMF service deletes the subscription information from the database before sending the response to the REST-EP.

4

The REST-EP forwards the response as 204 to the peer node.

5

The AMF service sends the request to NGAP-EP to remove the existing subscription from the NGAP-EP.