9A  Service Based Interface for 5G System |R15|  Word‑p. 86

9A.1  Introduction

Within the 5GCN, the AMF offers services to the CBCF via the Namf service-based interface (see TS 23.501 and TS 23.502).

Figure 9A.1-1 depicts the 5GS PWS system architecture, using the service-based interface representation showing how the network functions interact with each other.

Figure 9A.1-1: 5GS PWS system architecture - CBCF/PWS-IWF - AMF

Service-based interface to support 5GS PWS:

Namf:

Service-based interface exhibited by AMF.

The Table 9A.1-1 shows the AMF Service and Service Operations specific for PWS:

Table 9A.1-1: AMF Service for PWS

Service Name	Service Operations	Operation Semantics	Consumer
Namf_Communication	NonUeN2MessageTransfer	Request/Response	CBCF, PWS-IWF
	NonUeN2InfoSubscribe	Subscribe/Notify	CBCF, PWS-IWF
	NonUeN2InfoUnSubscribe	Subscribe/Notify	CBCF, PWS-IWF
	NonUeN2InfoNotify	Subscribe/Notify	CBCF, PWS-IWF

9A.2  Namf_Communication Service  Word‑p. 87

9A.2.1  Service Description

The Namf_Communication service is specified in TS 23.502, subclause 5.2.2.2.

9A.2.2  Service Operations

9A.2.2.1  Namf_Communication_NonUeN2MessageTransfer service operation

The Namf_Communication_NonUeN2MessageTransfer service operation is specified in TS 23.502, subclause 5.2.2.2.17.

The NonUeN2MessageTransfer service operation shall be invoked by the NF Service Consumer (e.g. CBCF or PWS-IWF) to initiate or stop broadcast in one or more cells as indicated in the Warning Area IE. The AMF shall accept the request and respond to the NF Service Consumer immediately.

When NonUeN2MessageTransfer service operation is used for PWS services:

1. PWS Write-Replace-Warning Request message (see subclause 9.2.26) or the Stop-Warning Request message (see subclause 9.2.28) are transferred in an N2 Message Container via the NonUeN2MessageTranfer request operation (along with a number of IEs);
   The N2 Message Container contains all the available elements from the Write-Replace-Warning Request message or the Stop-Warning Request message with the exception of the List of TAIs IE and the Send Write-Replace-Warning Indication IE or the Send Stop-Warning Indication IE. The PWS message in the N2 Message Container is sent by the AMF via N2 to NG-RAN.
2. Write-Replace-Warning Confirm message (see subclause 9.2.27) or the Stop-Warning Confirm message (see subclause 9.2.29) returned to the NF Service Consumer via the NonUeN2MessageTranfer response operation;
3. the List of TAIs IE shall be used by the AMF to determine to which NG-RAN nodes the N2 Message Container needs to be forwarded to. The List of TAIs IE is not included in the N2 Message Container. If the List of TAIs IE is not present then the message shall be forwarded to all NG-RAN nodes served by the AMF, subject to the RAT Selector NG-RAN;
4. each NonUeN2MessageTransfer message is uniquely identified by the Message Identifier IE, the Serial Number IE and the Message Type IE. These IEs are also included in the N2 Message Container;
5. if the Send Write-Replace-Warning-Indication IE is present in the Write-Replace-Warning Request message then the AMF shall send the associated Write-Replace-Warning Indication message(s) to the NF Service Consumer as specified in subclause 9A.2.2.3. The Send Write-Replace-Warning-Indication IE is not included in the N2 Message Container, and
6. if the Send Stop-Warning-Indication IE is present in the Stop-Warning Request message then the AMF shall send the associated Stop-Warning Indication message(s) to the NF Service Consumer as specified in subclause 9A.2.2.3. The Send Stop-Warning-Indication IE is not included in the N2 Message Container.

9A.2.2.2  Namf_Communication_NonUeN2InfoSubscribe service operation  Word‑p. 88

The Namf_Communication_NonUeN2InfoSubscribe service operation is specified in TS 23.502, subclause 5.2.2.2.18.

The NonUeN2InfoSubscribe service operation shall be invoked by the NF Service Consumer (e.g. CBCF or PWS-IWF) to subscribe to the delivery of non-UE specific PWS information from the NG-RAN node, e.g. for PWS events, sent via N2 to the AMF.

When NonUeN2InfoSubscribe service operation is used for PWS services:

1. The NF Service Consumer ID is an identifier which is configured in the CBCF or PWS-IWF;
2. The N2 information types are:
   • WarningIndications;
   • RestartFailure;
3. if the N2 information type is WarningIndications then the NF Service Consumer subscribes to receiving Write-Replace-Warning Indication messages (see subclause 9.2.30) and Stop-Warning Indication messages (see subclause 9.2.31) from the AMF, and
4. if the N2 information type is RestartFailure then the NF Service Consumer subscribes to receiving Restart Indications (see subclause 9.2.32) and Failure Indications (see subclause 9.2. 33) from the NG-RAN node.

9A.2.2.2A  Namf_Communication_NonUeN2InfoUnSubscribe service operation |R16|

The Namf_Communication_NonUeN2InfoUnSubscribe service operation is specified in TS 23.502, subclause 5.2.2.2.19.

The NonUeN2InfoUnSubscribe service opration shall be invoked by the NF Service Consumer (e.g. CBCF or PWS IWF) to unsubscribe to stop notifying non-UE specific N2 information from the NG-RAN node, e.g. for PWS events.

9A.2.2.3  Namf_Communication_NonUeN2InfoNotify service operation

The Namf_Communication_NonUeN2InfoNotify service operation is specified in TS 23.502, subclause 5.2.2.2.20.

The NonUeN2InfoNotify service operation is used by AMF to notify a particular PWS event towards the NF Service Consumer (e.g. CBCF or PWS-IWF) that has subscribed for the specific information. The AMF receives messages for such PWS events from NG-RAN via N2.

When NonUeN2InfoNotify service operation is used for PWS services, the N2 information consists of all (mandatory and optionally) available information provided via N2 in the Write-Replace Warning Indication (see subclause 9.2.30), a Stop Warning Indication (see subclause 9.2.31), a PWS Restart Indication (see subclause 9.2.32) or a PWS Failure Indication (see subclause 9.2.33).

9A.2.3  Service operation message flows

9A.2.3.1  Service flow for message transfer

Write-Replace-Warning Request messages and Stop-Warning-Request messages are transported with the NonUeMessageTransfer service operation. The procedure is shown in Figure 9A.2.3.1-1.

Figure 9A.2.3.1-1: Message tranfer procedure

Step 1.

If the CBCF supports reception of Wrtite-Replace-Warning Notifications and Stop-Warning Notifications then the CBCF uses the Namf_Communication_NonUeInfoSubscribe service operation to subscribe to these notifications.

Step 2a.

The CBCF sends a Write-Replace-Warning Request message or a Stop-Warning-Request message to the AMF using the Namf_Communication_NonUeN2MessageTransfer service operation.

Step 2b.

The AMF returns a Namf_Communication_NonUeN2MessageTransfer response message.

Step 3.

The AMF determines from the List of TAIs IE to the NG-RAN nodes the N2 Message Container shall be forwarded to.

Step 4.

The AMF forwards the messages included in the N2 Message Container to the selected NG-RAN nodes via N2 and receives a response from the NG-RAN nodes.

Step 5.

The AMF may aggregate the responses it has received from the NG-RAN nodes.

Step 6.

The AMF forwards the (aggregated) response(s) as Write-Replace-Warning Notification(s) or Stop-Warning Notifications to the CBCF using the Namf_Communication_NonUeNotify service operation if the CBCF has subscribed to receiving these notificatins in step 1.

9A.2.3.2  Service flow for Restart and Failure Indication messages  Word‑p. 89

Restart and Failure Indications are send by NG-RAN nodes and are forwarded to the CBCF by the AMF if the CBCF has subscribed to receiving such indications. The procedure is shown in Figure 9A.2.3.2-1.

Figure 9A.2.3.2-1: Indication message transfer procedure

Step 1.

If the CBCF supports reception of Restart Indication messages and Failure Indication messages then the CBCF uses the Namf_Communication_NonUeInfoSubscribe service operation to subscribe to these notifications.

Step 2.

A RAN Node sends a Restart Indication or a Failure Indication to the AMF.

Step 3.

The AMF forwards the Restart Indication or a Failure Indication to the CBCF using the Namf_Communication_NonUeInfoNotify service operation.

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