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Content for  TS 23.041  Word version:  17.0.0

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9.1.3.4  Warning Message Delivery Procedure in E-UTRAN |R8|Word‑p. 25
9.1.3.4.1  General
The maximum size of the warning message for E-UTRAN is different from that for UTRAN/GERAN.
When S1-flex is used, the eNodeB 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.
E-UTRA connected to both EPC and 5GCN (see TS 36.300) may receive warning messages from both EPC and 5GCN. Duplicated messages can be detected by checking the message identifier and serial number fields and duplicate messages shall not be transmitted on the radio interface.
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9.1.3.4.2  Warning Message Delivery Procedure
The warning message to be broadcast is delivered via MMEs to multiple eNodeBs. The eNodeB(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 9.1.3.4.2-1:
Reproduction of 3GPP TS 23.041, Figure 9.1.3.4.2-1: Warning message delivery procedure in E-UTRAN
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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 CBC shall authenticate this request.
Step 2.
Using the "impacted area" information, the CBC identifies which MMEs need to be contacted and determines the information to be place into the Warning Area List Information Element. The CBC sends a Write-Replace Warning Request message containing the warning message to be broadcast and the delivery attributes (Message identifier, Serial Number, list of TAIs, Warning Area List, OMC ID, CWM Indicator, Send Write-Replace-Warning-Indication, Global eNB ID, Warning Area Coordinates) to MMEs.
The warning messages use the coding scheme for CBS data specified in TS 23.038.
The list of TAIs is only used by the MME. The MME uses it for selecting which eNodeBs to forward the Write-Replace Warning Request message to.
If the Write-Replace Warning Request message is sent to reload cells served by an eNodeB, for which the CBC has previously received a Restart Indication (see subclause 15A.1 of TS 23.007), the CBC shall include the Global eNB ID IE with the identity of this eNodeB in the Write-Replace Warning Request message.
The Warning Area List shall be a list of Cell IDs or a list of TAIs or one or more Emergency Area IDs. The Warning Area List is only used by the eNodeB. The eNodeB is configured with the TAI(s) and Cell ID(s) it serves and the Emergency Area ID(s) that it belongs to. The eNodeB checks for any match of the contents of the Warning Area List with these IDs to identify the cells where to distribute the warning message. The Warning Area List is an optional information element. If the Warning Area is absent, it shall be interpreted as "all cells on the eNodeB". The number of cell IDs will be limited by the message size on SBc and S1-MME. 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 CBC is an operator option.
CBC shall set the Concurrent Warning Message (CWM) indicator in all Write-Replace Warning Request messages, if the PLMN supports concurrent warning message broadcasts.
The CBC shall not include the "digital signature" or "timestamp" information.
CBC shall set the Send Write-Replace-Warning Indication element in case the MME is requested to forward the Broadcast Scheduled Area List in a Write-Replace Warning Indication for the warning message.
CBC includes the Warning Area Coordinates in the Write-Replace-Warning Request message based on operator policy.
Step 3.
The MME sends a Write-Replace Warning Confirm message that indicates to the CBC that the MME has started to distribute the warning message to eNodeBs.
The Write-Replace Warning Confirm message may contain the Unknown Tracking Area List IE. The Unknown Tracking Area List IE identifies the Tracking Areas that are unknown to the MME and where the Request cannot be delivered.
If this message is not received by the CBC within an appropriate time period, the CBC can attempt to deliver the warning message via another MME in the same pool area.
Step 4.
Upon reception of the Write-Replace Confirm messages from the MMEs, the CBC may confirm to the CBE that it has started to distribute the warning message.
Step 5.
The MME forwards Write-Replace Warning Message Request to eNodeBs. The MME shall use the list of TAIs to determine the eNodeBs in the delivery area. If the list of TAIs is not included and no Global eNB ID has been received from the CBC, the message is forwarded to all eNodeBs that are connected to the MME. If a Global eNB ID has been received from the CBC, the MME shall forward the message only to the eNodeB indicated by the Global eNB ID IE.
Step 6.
When S1-flex is used the eNodeB may receive same message from multiple MMEs. The eNodeB 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 eNodeB shall use the Warning Area List information to determine the cell(s) in which the message is to be broadcast. The eNodeBs return a Distribute Warning Message Response to the MME, 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 Message Request, the eNodeB does not stop existing broadcast message but start broadcasting the new message concurrently. Otherwise the eNodeB shall immediately replace the existing broadcast message with the newer one.
The eNodeB broadcasts the message frequently according to the attributes set by the CBC 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 and it is configured in the MME based on operator policy, the MME shall forward the Broadcast Scheduled Area Lists in a Write-Replace Warning Indication(s) to the CBC. The Broadcast Scheduled Area List shall contain the Broadcast Completed Area List the MME has received from the eNodeB. The MME may aggregate Broadcast Completed Area Lists it receives from eNodeBs.
Step 9.
From the Write-Replace Warning Response messages returned by eNodeB's the MME 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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9.1.3.4.3  Warning Message Cancel Procedure |R9|Word‑p. 29
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 9.1.3.4.3-1: Warning message cancel procedure in E-UTRAN
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Step 1.
CBE initiates procedure by sending Stop Emergency Broadcast Request (e.g. "Message Identifier and Serial Number"), to the CBC. The CBC shall authenticate this request.
Step 2.
The CBC identifies which MMEs need to be contacted and determines the information to be place into the Warning Area Information Element. The CBC sends a Stop Warning Request message (Message Identifier, Serial Number, Tracking Area ID list, Warning Area, OMC ID, Send Stop Warning Indication) to MMEs.
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 CBC is an operator option.
The CBC sets the Send Stop Warning Indication element in case the MME is requested to forward the Broadcast Completed Area List in a Stop Warning Indication for the warning message.
Step 3.
The MME sends a Stop Warning Confirm message that indicates to the CBC that the MME has started to distribute the Kill Request message to eNodeBs.
If this message is not received by the CBC within an appropriate time period, the CBC can attempt to send Stop Warning Request via another MME in the same pool area.
Step 4.
Upon reception of the Stop Warning Confirm messages from the MMEs, the CBC may confirm to the CBE that it has initiated the Warning message cancel procedure.
Step 5.
The MME forwards the request from the CBC by Kill Request to eNodeB's. The MME shall use the Tracking Area ID list to determine the eNodeBs that may have warning message broadcast ongoing. In case the Tracking Area ID list is not included the Kill Request is forwarded to all eNodeBs that are connected to the MME.
Step 6.
The eNodeB shall stop 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 eNodeB").
When S1-Flex is used the eNodeB may receive same Kill Request from multiple MMEs, if any redundant Kill Requests are detected only the response to the first MME shall contain statistics related to the cancelled broadcast.
Step 7.
If the Send Stop Warning Indication parameter was present in the Stop Warning Request and it is configured in the MME based on operator policy, the MME forwards the Broadcast Cancelled Area List it has received from the eNodeB in a Stop Warning Indication(s) to the CBC. The MME may aggregate Broadcast Cancelled Area Lists it receives from eNodeBs.
If the CBC has requested the MME to send Stop Warning Indications, then the CBC releases the Serial Number of a message after it has stopped receiving the Stop Warning Indications for that message.
Step 8.
From the Kill Response messages returned by eNodeB's the MME 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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