9.1 Requirements on Core Network and Radio Access Network

23.0413GPPRelease 18Technical realization of Cell Broadcast Service (CBS)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

9.1.1 GSM Radio Access Network

Commands interpreted by the BSC will result in a sequence of 4 SMS BROADCAST REQUEST messages or 1 SMS BROADCAST COMMAND message being sent to a BTS, which in turn result in a sequence of 4 blocks each 22 octets long being transferred via the BTS-MS interface (see 3GPP TS 44.012 [7]).

With the SMS BROADCAST REQUEST mode of operation, the 88 octet fixed length CBS page which is specified in clause 9.3 is split into four 22 octet blocks which are carried in SMS BROADCAST REQUEST messages as follows:

octets 1‑22 are transferred in the 1^st SMS BROADCAST REQUEST

with a sequence number (see 3GPP TS 44.012 [7]) indicating first block;

octets 23‑44 are transferred in the 2^nd SMS BROADCAST REQUEST

with a sequence number (see 3GPP TS 44.012 [7]) indicating second block;

octets 45‑66 are transferred in the 3^rd SMS BROADCAST REQUEST

with a sequence number (see 3GPP TS 44.012 [7]) indicating third block;

octets 67‑88 are transferred in the 4^th SMS BROADCAST REQUEST

with a sequence number (see 3GPP TS 44.012 [7]) indicating fourth block.

Figure 3 illustrates the protocol architecture and the scope of the various GSM Specifications for the SMS BROADCAST REQUEST mode of operation.

Figure 3

With the SMS BROADCAST COMMAND mode of operation, the BSC sends to the BTS in one single message the 88 octet fixed length CBS page. The BTS then splits the page into four 22 octet blocks, adds the sequence number (see 3GPP TS 44.012 [7]) and transmits the four resulting blocks on the air.

Figure 4 illustrates the protocol architecture and the scope of the various GSM Specifications for the SMS BROADCAST COMMAND mode of operation.

Figure 4

9.1.2 UMTS Radio Access Network

Commands interpreted by the RNC will result in one SMS BROADCAST COMMAND sent to the UE. The CBS messages are completely transparent to the Node B, i.e. no manipulation of the data like e.g. fragmentation is done at the Node B.

Figure 4a

9.1.3 Warning Message Delivery

9.1.3.1 General

In GSM and UMTS, the cell broadcast service can be used to transfer CBS messages related to public warning. This requires reception of CBS messages to be permanently activated in the mobile terminal.

Warning message delivery is similar to cell broadcast service. It permits a number of unacknowledged warning messages to be broadcast to MS/UEs within a particular area. Reception of warning messages is enabled as defined later on in this specification.

For warning messages received from a PLMN, 3GPP TS 31.102 [18] defines a USIM data file for configuration of warning messages reception. In case of a non-existing or empty USIM data file, the MS/UE accepts all warning messages on all PLMNs. As specified in 3GPP TS 31.102 [18], the MS/UE can be configured to ignore all warning messages received in its HPLMN or in a PLMN equivalent to it. As specified in 3GPP TS 31.102 [18], the MS/UE can be configured to ignore all warning messages received in a VPLMN or in a PLMN equivalent to it.

A UE in limited service state, and configured according to the USIM data file to display warning messages on that PLMN, shall display warning messages to the user.

For warning messages received from an SNPN:

– 3GPP TS 23.122 [49] defines configuration parameters in each entry of the "list of subscriber data" for configuration of warning message reception. In case the configuration parameters are not present in the selected entry of the "list of subscriber data", the UE accepts all warning messages on all SNPNs. As specified in 3GPP TS 23.122 [49], when using an entry of the "list of subscriber data" to access an SNPN, the UE can be configured to ignore all warning messages received in the subscribed SNPN of the selected entry of the "list of subscriber data". As specified in 3GPP TS 23.122 [49], when using an entry of the "list of subscriber data" to access an SNPN, the UE can be configured to ignore all warning messages received in an SNPN other than the subscribed SNPN of the selected entry of the "list of subscriber data"; and

– 3GPP TS 31.102 [18] defines a USIM data file for configuration of warning message reception when the UE accesses an SNPN using the PLMN subscription. In case of a non-existing or empty USIM data file, the UE accepts all warning messages on all SNPNs. As specified in 3GPP TS 31.102 [18], the UE can be configured to ignore all warning messages received in an SNPN.

In GSM, an ETWS capable MS uses the procedure as outlined in clause 9.1.3.2. See 3GPP TS 44.018 [26] and 3GPP TS 44.060 [27] for details on the radio interface.

In UMTS, an ETWS capable UE uses the procedure as outlined in clause 9.1.3.3. See 3GPP TS 25.331 [16] for details on the radio interface.

In E-UTRAN, an ETWS capable UE or a CMAS capable UE uses the procedures as outlined in clause 9.1.3.4. See 3GPP TS 36.331 [36] for details on the radio interface.

In NG-RAN, an ETWS capable UE or a CMAS capable UE uses the procedures as outlined in clause 9.1.3.5. See 3GPP TS 36.331 [36] and 3GPP TS 38.331 [48] for details on the radio interface.

9.1.3.2 Warning Message Delivery Procedure in GSM

When a warning message is sent in GERAN, the following message flow applies. The warning message request from the CBE will trigger a broadcast of an ETWS emergency message (containing the ETWS Primary Notification) and/or a CBS message (constituting a Secondary Notification) on the radio interface. The ETWS emergency message is conveyed by the paging message which can invoke mobile terminals to start receiving CBS messages without MMI. Mobile stations invoked to start receiving CBS messages this way may stop receiving CBS messages (without MMI) after a predefined period of time.

Figure 9.1.3.2-1: Warning message delivery procedure in GERAN

1. Network registration and security procedures are performed.

NOTE 1: This step is performed each time an MS is attached to a NW (e.g. after each power-on).

2. CBE (e.g. Information Source such as PSAP or Regulator) sends emergency information ("warning type", "warning message", "impacted area", and "time period") to the CBC. The CBC shall authenticate this request. The "warning type" takes one of the following values: earthquake, tsunami, earthquake and tsunami, test, or other.

3. Using the "impacted area information", the CBC identifies which BSCs need to be contacted and constructs the "Cell list" for the cells in which the information is to be broadcast.

The CBC shall send a WRITE-REPLACE message to all the identified BSCs. If the emergency information received from the CBE contains warning information to be sent both in an ETWS emergency message and in a CBS message, then the CBC need to send this information in separate WRITE-REPLACE messages to the identified BSCs accordingly:

– When containing an ETWS emergency message the WRITE-REPLACE message includes the "Paging ETWS Indicator" to differentiate it from a normal CBS message, as well as (among other parameters) the "Cell list", "warning type" (which constitutes a part of the ETWS Primary Notification message, see clause 9.4.1.3), and the "warning period" parameter.

– When containing a CBS message the WRITE-REPLACE message includes the "Channel Indicator" to differentiate it from an ETWS emergency message, as well as (among other parameters) the "Cell list", "Repetition Period", "No of Broadcasts Requested" and the "CBS Message Information" parameter(s).

The CBC shall not include the "digital signature" or "timestamp" information.

NOTE 2: Due to requirements in earlier versions of this document, it is possible for "digital signature" and "timestamp" information (included in the "Warning Security Information" parameter) to be transmitted within the WRITE-REPLACE message.

4. The BSCs use the "Cell list" information to identify in which cells the warning message needs to be broadcasted.

a) When the WRITE-REPLACE message contains an ETWS emergency message, the BSC/BTS:

1) shall include the ETWS emergency message within the paging message and start sending the paging messages in all paging groups for the time duration requested by the CBC in the "warning period" parameter. The paging message contains the "ETWS indicator", based on the "Paging ETWS Indicator" received in the WRITE-REPLACE message, and the ETWS Primary Notification message as defined in clause 9.4.1.3. When the "warning type" in the ETWS Primary Notification message is set to ‘other’, all of the warning information is included in the broadcasted CBS message.

2) may send the ETWS Primary Notification message in other messages (Application Information, see 3GPP TS 44.018 [26], and Packet Application Information, see 3GPP TS 44.060 [27]) in order to reach mobiles in connected mode.

b) When the WRITE-REPLACE message contains a CBS message the BSC/BTS shall start to broadcast the CBS message on the Cell Broadcast channel according to the "Repetition Period" and "No of Broadcasts Requested" requested by the CBC.

5. Upon reception of the paging message containing the ETWS Primary Notification message, if the MS is configured to accept warnings on that PLMN (see 3GPP TS 31.102 [18]) the ETWS capable MS alerts the user immediately as indicated by the "warning type" value, and starts reading the Cell Broadcast channel in order to acquire a possible broadcasted CBS message containing the Secondary Notification message.

Upon reception of the CBS message containing the Secondary Notification message, the ETWS capable MS immediately indicates the contents of the Secondary Notification message to the user.

NOTE 3: If the MS receives the same ETWS Primary Notification message more than once it silently discards the last received Primary Notification message.

NOTE 4: When the "warning type" is set to ‘test’, the MS silently discards the ETWS Primary Notification message. The MS does not start reading the Cell Broadcast channel in this case. However, the MS specially designed for testing purposes can perform user alerting and proceed to the reception of the broadcasted CBS message as described above.

NOTE 5: If the MS is configured to ignore warnings on that PLMN (see 3GPP TS 31.102 [18]), the MS does not try to acquire the broadcasted CBS message described above.

The MS shall perform duplication detection of the received message as specified in clause 8.2.

The MS shall ignore the values of "digital signature" and "timestamp" if received in the "Warning Security Information" parameter.

6. The BSC sends a WRITE-REPLACE COMPLETE message to the CBC in response to the WRITE-REPLACE message.

7. CBC sends acknowledgement message to CBE.

9.1.3.3 Warning Message Delivery Procedure in UMTS

When a warning message is sent in UTRAN, the following message flow applies. In this case, the paging message with a new emergency indication can invoke mobile terminals to start receiving CBS messages without MMI. Mobile stations invoked to start receiving CBS messages this way may stop receiving CBS messages (without MMI) after a period of time, which should not be less than 30 minutes in case DRX-Level-2 is used, and 2 minutes in case DRX-Level-1 is used.

Figure 9.1.3.3-1: Warning message delivery procedure in UTRAN

1. Network registration and security (e.g. mutual authentication) procedures are performed.

NOTE 1: This step is performed each time a UE is attached to a network (e.g. after each power-on).

3. Using the "impacted area information", the CBC identifies which RNCs need to be contacted and constructs the "Service Area ID list" for the cells in which the information is to be broadcast.

The CBC shall send a WRITE-REPLACE message to all the identified RNCs. The message shall include an "emergency indication" to differentiate it from normal Cell Broadcast information, as well as the "Service Area ID list", "warning type", "warning message".

The CBC shall not include the "digital signature" or "timestamp" information.

NOTE 2: Due to requirements in earlier versions of this document, it is possible for "digital signature" and "timestamp" information to be transmitted within "warning message".

4. The RNCs use the "Service Area ID list" information to identify which Node Bs they need to reach, and then, they relay information to them using the appropriate Iub interface message.

5. The Node B receives the Iub message containing the emergency indication. As parallel actions, the RNC/Node B:

a) shall start to broadcast the "warning message". This is broadcast by using a Cell Broadcast channel and modified System Information messages. This broadcast information is repeated continuously by the Node B for the "time period" requested by the CBE.

b) shall use paging messages in every paging group to alert idle mode mobiles to receive the broadcast warning message. Typically these paging messages are repeated in all paging groups for several DRX periods. The paging message contains the "ETWS indication" based on the "warning type" information. When the "warning type" is set to ‘other’, all of the warning information is included in the broadcast "warning message".

c) may send the "ETWS indication" in other messages (System Information Change Indication or ETWS Primary Notification With Security) in order to reach mobiles in connected mode. Inclusion of "ETWS indication" is the same as that of the paging message mentioned above.

6. If the UE is configured to accept warnings on that PLMN (see 3GPP TS 31.102 [18]) the UE alerts the user immediately, using "warning type" value upon the reception of the "ETWS Indication".

NOTE 3: If the UE received the "ETWS Indication" more than once it will silently discard the optional primary notification.

NOTE 4: When the "warning type" is ‘test’, the UE silently discards the "ETWS Indication" and does not perform the reception of the broadcast message described below. However, the UE specially designed for testing purposes can perform user alerting described above and proceed to the reception of the broadcast message described below

NOTE 5: If the UE is configured to ignore warnings on that PLMN (see 3GPP TS 31.102 [18]) the UE does not perform the reception of the broadcast message described below.

Upon the reception of the"ETWS Indication", the UE activates the reception of the broadcast messages containing the "warning message" as the secondary notification. The UE indicates the contents of the "warning message" to the user.

The UE shall perform duplication detection of the received message as specified in clause 8.2.

The UE shall ignore the values of "digital signature" and "timestamp" if received.

NOTE 6: The "digital signature" and "timestamp" can be received due to requirements in earlier versions of this document.

7. The RNC node sends a BMC REPORT-SUCCESS to the CBC in response to Write-Replace.

8. CBC sends acknowledgement message to CBE.

9.1.3.4 Warning Message Delivery Procedure in E-UTRAN

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 3GPP TS 36.300 [46]) 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.

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:

Figure 9.1.3.4.2-1: Warning message delivery procedure in E-UTRAN

0. Network registration and security (e.g. mutual authentication) procedures are performed.

NOTE 1: This step is performed each time a UE is attached to a network (e.g. after each power on).

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.

NOTE 2: A warning message can include a language-independent content mapped to an event or a disaster that is compatible with texts used to describe user information contained in the content of a CBS-Message-Information-Page transparently passed from CBC to UEs if the ePWS language-independent content functionality (see clause 8.3) is supported by CBE.

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 3GPP TS 23.038 [3].

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 clause 15A.1 of TS 23.007 [38]), 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.

NOTE 3: Due to requirements in earlier versions of the specification, it is possible that "digital signature" and "timestamp" information are transmitted within the "warning message".

CBC includes the Warning Area Coordinates in the Write-Replace-Warning Request message based on operator policy.

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.

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.

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.

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.

NOTE 4: If concurrent warning messages are not supported, this requires the CBE/CBC to take care that ‘lower’ priority warnings are not sent while a higher priority warning is still being sent.

The eNodeB broadcasts the message frequently according to the attributes set by the CBC that originated the warning message distribution.

7. If the UE has been configured to receive warning messages, and the UE is configured to accept warnings on that PLMN (see 3GPP TS 31.102 [18]), 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 clause 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, 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:

1) if 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:

a) the UE:

i) is able to determine its location and determines it is inside the Warning Area Coordinates of the stored "warning message"; or

ii) 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; or

b) the UE is able to determine its location and determines it is outside the Warning Area Coordinates of the stored "warning message", discard the geo-fencing trigger message; or

2) if none of Serial Number and Message Identifier combinations of the stored "warning message" matches any of the Serial Number and Message Identifier combinations included in the Warning Message Content IE (CB Data) of the geo-fencing trigger message, 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 clause 8.3) and which are capable of displaying text-based warning messages should be capable of displaying the entire warning message that they receive.

Editor’s note [WI: ePWS, CR#203]: FFS on what character(s) such as Unicode based pictogram(s) are the language-independent content mapped to an event or a disaster.

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.

NOTE 5: Support for sending of Write-Replace Warning Indication(s) to the CBC is optional in the MME.

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.

9.1.3.4.3 Warning Message Cancel Procedure

The cancel warning message delivery procedure takes place when CBE requests to stop the on-going broadcast of warning messages.

Figure 9.1.3.4.3-1: Warning message cancel procedure in E-UTRAN

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.

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.

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.

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.

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.

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.

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.

NOTE: Support for Stop Warning Indication(s) is optional in the MME.

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.

9.1.3.5 Warning Message Delivery Procedure in NG-RAN

9.1.3.5.1 General

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.

9.1.3.5.2 Warning Message Delivery Procedure

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:

Figure 9.1.3.5.2-1: Warning message delivery procedure in NG-RAN

0. Network registration and security (e.g. mutual authentication) procedures are performed.

NOTE 1: This step is performed each time a UE is attached to a network (e.g. after each power on).

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 3GPP TS 23.038 [3].

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 clause 15A.1 of TS 23.007 [38]), 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 or SNPN.

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 or SNPN 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.

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.

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.

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.

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.

NOTE 3: If concurrent warning messages are not supported, this requires the CBE/CBCF to take care that ‘lower’ priority warnings are not sent while a higher priority warning is still being sent.

The NG-RAN node broadcasts the message frequently according to the attributes set by the CBCF that originated the warning message distribution.

7. If the UE has been configured to receive warning messages, and the UE is configured to accept warnings on that PLMN (see 3GPP TS 31.102 [18]) or SNPN (see 3GPP TS 23.122 [49]), then the UE proceeds as follows:

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:

If the "warning message" is a geo-fencing trigger message (see clause 9.4.1.2.2) then:

a) the UE:

i) is able to determine its location and determines it is inside the Warning Area Coordinates of the stored "warning message"; or

ii) is unable to determine its location,

b) the UE is able to determine its location and determines it is outside the Warning Area Coordinates of the stored "warning message", discard the geo-fencing trigger message; or

– 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.

Editor’s note [WI: ePWS, CR#203]: FFS on what character(s) such as Unicode based pictogram(s) are the language-independent content mapped to an event or a disaster.

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.

NOTE 4: Support for sending of Write-Replace Warning Indication(s) NG-RAN to the CBCF is optional in the AMF.

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.

9.1.3.5.3 Warning Message Cancel Procedure

The cancel warning message delivery procedure takes place when CBE requests to stop the on-going broadcast of warning messages.

Figure 9.1.3.5.3-1: Warning message cancel procedure in NG-RAN

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.

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.

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.

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.

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.

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.

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.

NOTE: Support for Stop Warning Indication(s) NG-RAN is optional in the AMF.

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.

9.1.4 UMTS Protocol Overview

Figure 5

9.1.5 E-UTRAN Protocol Overview

Legend:

– SBc Application Protocol (SBc-AP): Application Layer Protocol between CBC and MME. This protocol supports transfer of warning messages.

– S1 Application Protocol (S1-AP): Application Layer Protocol between the eNodeB and the MME.

– SCTP for the control plane (SCTP): This protocol guarantees delivery of signalling messages between MME and eNodeB (S1). SCTP is defined in RFC 4960 [33].

Figure 9.1.5-1: CBC – eNodeB

9.1.6 NG-RAN Protocol Overview

Figure 9.1.6-1: CBCF – NG-RAN

Legend:

– NG application protocol information for cell broadcast (NG-AP-CB): Subset of NG-AP information that the AMF relays between the AN and the CBCF. NG-AP-CB corresponds to a subset of NG-AP defined in 3GPP TS 38.413 [40].

– NG application protocol (NGAP): Application layer protocol between the NG-RAN node and the AMF. The NGAP protocol is defined in 3GPP TS 38.413 [40].

– SCTP for the control plane (SCTP): This protocol guarantees delivery of signalling messages between AMF and NG-RAN (N2). SCTP is defined in IETF RFC 4960 [33].

– HTTP/2: Application layer protocol for Service based interface between AMF and CBCF. HTTP/2 is defined in IETF RFC 7540 [42].

NOTE: NG-RAN protocol stack for the case where AMF and CBC inter-connects via PWS-IWF is described in annex B.3.