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Content for  TS 23.041  Word version:  17.0.0

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9.1.3.5  Warning Message Delivery Procedure in NG-RAN |R14|Word‑p. 30
9.1.3.5.1  General |R15|
The maximum size of the warning message for NG-RAN is the same as the maximum size defined for E-UTRAN.
When the CBCF sends warning messages to multiple AMFs for the same warning area, the gNodeB may receive duplicated warning messages. Duplicated messages can be detected by checking the message identifier and serial number fields and they shall not be transmitted on the radio interface.
The Warning Message Delivery procedure messages and the Warning Message Cancel procedure messages are transported with the NonUeN2MessageTransfer service operation between CBCF and AMF (see clause 9A) and via N2 between AMF and NG-RAN.
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9.1.3.5.2  Warning Message Delivery Procedure |R15|
The warning message to be broadcast is delivered via AMFs to multiple NG-RAN nodes. The NG-RAN node(s) are responsible for scheduling the broadcast of the new message and the repetitions in each cell.
The overall warning message delivery procedure is presented in figure 9.1.3.5.2-1:
Reproduction of 3GPP TS 23.041, Figure 9.1.3.5.2-1: Warning message delivery procedure in NG-RAN
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Step 0.
Network registration and security (e.g. mutual authentication) procedures are performed.
Step 1.
CBE (e.g. Information Source such as PSAP or Regulator) sends emergency information (e.g. "warning type", "warning message", "impacted area", "time period") to the CBC. The CBCF shall authenticate this request.
Step 2.
Using the "impacted area" information, the CBCF identifies which AMFs need to be contacted and determines the information to be placed into the Warning Area List NG-RAN Information Element. The CBCF sends a Write-Replace Warning Request NG-RAN message containing the warning message to be broadcast and the delivery attributes (Message Identifier, Serial Number, list of NG-RAN TAIs, Warning Area List NG-RAN, OMC ID, CWM Indicator, Send Write-Replace-Warning-Indication, Global RAN Node ID, Warning Area Coordinates) to AMFs.
The warning messages use the coding scheme for CBS data specified in TS 23.038.
The list of NG-RAN TAIs is only used by the AMF. The AMF uses it for selecting which NG-RAN node(s) to forward the Write-Replace Warning Request NG-RAN message to.
If the Write-Replace Warning Request NG-RAN message is sent to reload cells served by a NG-RAN node, for which the CBCF has previously received a Restart Indication (see subclause 15A.1 of TS 23.007), the CBCF shall include the Global RAN Node ID IE with the identity of this NG-RAN node in the Write-Replace Warning Request NG-RAN message.
The Warning Area List NG-RAN shall be a list of Cell IDs or a list of NG-RAN TAIs or one or more Emergency Area IDs. The Warning Area List NG-RAN is only used by the NG-RAN node. The NG-RAN node is configured with the NG-RAN TAI(s) and Cell ID(s) it serves and the Emergency Area ID(s) that it belongs to. The NG-RAN node checks for any match of the contents of the Warning Area List NG-RAN with these IDs to identify the cells where to distribute the warning message. The Warning Area List NG-RAN is an optional information element. If the Warning Area List NG-RAN is absent, it shall be interpreted as "all cells on the NG-RAN node". The number of cell IDs will be limited by the message size on N50 and N2. An Emergency Area ID is unique within the PLMN.
The message may include an OMC ID. If present, it indicates the OMC to which the Trace record generated in step 9 is destined. Co-location of that OMC with the CBCF is an operator option.
The CBCF shall set the Concurrent Warning Message (CWM) indicator in all Write-Replace Warning Request NG-RAN messages, if the PLMN supports concurrent warning message broadcasts.
The CBCF shall not include the "digital signature" or "timestamp" information.
The CBCF shall set the Send Write-Replace-Warning Indication element in case the AMF is requested to forward the Broadcast Scheduled Area List in a Write-Replace Warning Indication NG-RAN for the warning message.
The CBCF includes the Warning Area Coordinates in the Write-Replace-Warning-Request-NG-RAN message based on operator policy.
Step 3.
The AMF sends a Write-Replace Warning Confirm NG-RAN message that indicates to the CBCF that the AMF has started to distribute the warning message to NG-RAN nodes.
The Write-Replace Warning Confirm NG-RAN message may contain the Unknown Tracking Area List IE. The Unknown Tracking Area List IE identifies the Tracking Areas that are unknown to the AMF and where the Request cannot be delivered.
If this message is not received by the CBCF within an appropriate time period, the CBCF can attempt to deliver the warning message via another AMF in the same AMF region.
Step 4.
Upon reception of the Write-Replace Confirm NG-RAN messages from the AMFs, the CBCF may confirm to the CBE that it has started to distribute the warning message.
Step 5.
The AMF forwards Write-Replace Warning Message Request NG-RAN to NG-RAN nodes. The AMF shall use the list of NG-RAN TAIs to determine the NG-RAN nodes in the delivery area. If the list of NG-RAN TAIs is not included and no Global RAN Node ID has been received from the CBCF, the message is forwarded to all NG-RAN nodes that are connected to the AMF, subject to the RAT Selector NG-RAN. If a Global RAN Node ID has been received from the CBCF, the AMF shall forward the message only to the NG-RAN node indicated by the Global RAN Node ID IE.
Step 6.
When the CBCF sends warning messages to multiple AMFs for the same warning area, the NG-RAN node may receive the same message from multiple AMFs. The NG-RAN node detects duplicate messages by checking the message identifier and serial number fields within the warning message. If any redundant messages are detected only the first one received will be broadcasted by the cells. The NG-RAN node shall use the Warning Area List NG-RAN information to determine the cell(s) in which the message is to be broadcast. The NG-RAN nodes return a Write Replace Warning Message Response to the AMF, even if it was a duplicate.
If there is a warning broadcast message already ongoing and the CWM Indicator is included in the Write-Replace Warning Request NG-RAN message, the NG-RAN node does not stop the existing broadcast message but starts broadcasting the new message concurrently. Otherwise the NG-RAN node shall immediately replace the existing broadcast message with the newer one.
The NG-RAN node broadcasts the message frequently according to the attributes set by the CBCF that originated the warning message distribution.
Step 7.
If the UE has been configured to receive warning messages, and the UE is configured to accept warnings on that PLMN (see TS 31.102), then the UE proceeds as follows:
The UE can use "warning type" values, 'earthquake', 'tsunami' or 'earthquake and tsunami', immediately to alert the user. When "warning type" is 'test', the UE silently discards the primary notification, but the UE specially designed for testing purposes may proceed with the following procedures.
The UE activates reception of the broadcast messages containing the "warning message".
If the Warning Area Coordinates are not present:
The UE indicates the contents of the "warning message" to the user.
If the Warning Area Coordinates are present, and if the UE is unable to determine its location:
The UE indicates the contents of the "warning message" to the user.
If the Warning Area Coordinates are present, and the UE determines it is inside the Warning Area Coordinates:
The UE indicates the contents of the "warning message" to the user.
If the Warning Area Coordinates are present, and the UE determines it is outside the Warning Area Coordinates:
The UE does not indicate the contents of the "warning message" to the user. The UE shall store the "warning message" in the list of "warning messages" to be checked for geo-fencing during a UE implementation specific time which shall not be greater than 24 hours. Upon expiration of the UE implementation specific time, the UE shall remove the stored "warning message" from the list of "warning messages" to be checked for geo-fencing.
If the "warning message" is a geo-fencing trigger message (see subclause 9.4.1.2.2) then:
  • if the list of "warning messages" to be checked for geo-fencing stored at the UE is not empty, the UE shall, for each "warning message" stored at the UE in the list of "warning messages" to be checked for geo-fencing:
    1. compare the Serial Number and Message Identifier combination of the stored "warning message" to the list of Serial Number and Message Identifier combinations included in the Warning Message Content IE (CB Data) of the geo-fencing trigger message and encoded as specified in ATIS-0700041 [47]; and
    2. if:
      1. the Serial Number and Message Identifier combination of the stored "warning message" matches one of the Serial Number and Message Identifier combinations included in the geo-fencing trigger message; and
      2. the UE:
        1. is able to determine its location and determines it is inside the Warning Area Coordinates of the stored "warning message"; or
        2. is unable to determine its location,
      indicate the contents of the stored "warning message" to the user, remove the "warning message" from the list of "warning messages" to be checked for geo-fencing and then discard the geo-fencing trigger message; and
  • if the list of "warning messages" to be checked for geo-fencing stored at the UE is empty, the UE shall discard the geo-fencing trigger message.
If a language-independent content mapped to an event or a disaster (e.g. character such as Unicode based pictogram mapping to a disaster) is included as part of user information contained in the content of a CBS-Message-Information-Page transparently passed from CBC to UEs:
  • UEs with user interface which support the ePWS language-independent content functionality (see subclause 8.3) and which are capable of displaying text-based warning messages should be capable of displaying the entire warning message that they receive.
Step 8.
If the Send Warning-Message-Indication parameter was present in the Write-Replace Warning Request NG-RAN and it is configured in the AMF based on operator policy, the AMF shall forward the Broadcast Scheduled Area Lists in a Write-Replace Warning Indication(s) NG-RAN to the CBCF. The Broadcast Scheduled Area List shall contain the Broadcast Completed Area List the AMF has received from the NG-RAN node. The MME may aggregate Broadcast Completed Area Lists it receives from NG-RAN nodes.
Step 9.
From the Write-Replace Warning Response messages returned by NG-RAN nodes the AMF determines the success or failure of the delivery and creates a trace record. Any OMC ID received in step 2 is written to the trace record to permit the O&M system to deliver them to the desired destination.
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9.1.3.5.3  Warning Message Cancel Procedure |R15|Word‑p. 34
The cancel warning message delivery procedure takes place when CBE requests to stop the on-going broadcast of warning messages.
Reproduction of 3GPP TS 23.041, Figure 9.1.3.5.3-1: Warning message cancel procedure in NG-RAN
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Step 1.
CBE initiates procedure by sending Stop Emergency Broadcast Request (e.g. "Message Identifier and Serial Number"), to the CBCF. The CBCF shall authenticate this request.
Step 2.
The CBCF identifies which AMFs need to be contacted and determines the information to be placed into the Warning Area Information Element. The CBC sends a Stop Warning Request NG-RAN message (Message Identifier, Serial Number, Tracking Area ID list, Warning Area, OMC ID, Send Stop Warning Indication) to AMFs.
The message may include an OMC ID. If present, it indicates the OMC to which the Trace record generated in step 8 is destined. Co-location of that OMC with the CBCF is an operator option.
The CBCF sets the Send Stop Warning Indication element in case the AMF is requested to forward the Broadcast Completed Area List in a Stop Warning Indication NG-RAN for the warning message.
Step 3.
The AMF sends a Stop Warning Confirm NG-RAN message that indicates to the CBCF that the AMF has started to distribute the Cancel Request message to NG-RAN nodes.
If this message is not received by the CBCF within an appropriate time period, the CBCF can attempt to send Stop Warning Request NG-RAN via another AMF in the same AMF region.
Step 4.
Upon reception of the Stop Warning Confirm NG-RAN messages from the AMFs, the CBCF may confirm to the CBE that it has initiated the Warning message cancel procedure.
Step 5.
The AMF forwards the request from the CBCF by a Cancel Request to NG-RAN nodes. The AMF shall use the Tracking Area ID list to determine the NG-RAN nodes that may have warning message broadcast ongoing. In case the Tracking Area ID list is not included the Cancel Request is forwarded to all NG-RAN nodes that are connected to the AMF, subject to the RAT Selector NG-RAN.
Step 6.
The NG-RAN node shall cancel broadcasting the warning message identified by the Message Identifier and Serial Number in the areas identified by Warning Area IDs. If the Warning Area is absent, it shall be interpreted as "all cells on the NG-RAN node".
When the CBCF sends cancel messages to multiple AMFs for the same warning area, the NG-RAN node may receive same Cancel Request from multiple AMFs, if any redundant Cancel Requests are detected only the response to the first AMF shall contain statistics related to the cancelled broadcast.
Step 7.
If the Send Stop Warning Indication parameter was present in the Stop Warning Request NG-RAN and it is configured in the AMF based on operator policy, the AMF forwards the Broadcast Cancelled Area List it has received from the NG-RAN node in a Stop Warning Indication(s) NG-RAN to the CBCF. The AMF may aggregate Broadcast Cancelled Area Lists it receives from NG-RAN nodes.
If the CBCF has requested the AMF to send Stop Warning Indications NG-RAN, then the CBCF releases the Serial Number of a message after it has stopped receiving the Stop Warning Indications NG-RAN for that message.
8. From the Cancel Response messages returned by NG-RAN nodes the AMF creates a trace record (e.g. number of times a particular message has been broadcasted in a given warning area) related to the cancelled message. Any OMC ID received in step 2 is written to the trace record to permit the O&M system to deliver them to the desired destination.
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