5G System Learning - Alert Message Transmission

1. In 5G, alert messages typically refer to system health notifications and network-hazardous operations. They can also refer to legitimate emergency alerts, such as those sent via the 5G network's WEA (Wireless Emergency Alert) system to notify public safety of natural disasters and other events.

2. Message transmission typically uses a "write-replace" approach to initiate or override the broadcast of alert messages. Alert message transmission utilizes non-terminal-associated signaling. The successful operation process is shown in Figure 8.9.1.2-1 below, where:

• The AMF initiates this process by sending a "Write-Replace Alert Request" message to the NG-RAN node.
• Upon receiving a Write-Replace Warning Request message, the NG-RAN node shall prioritize allocating its resources to processing warning messages, where:

• ​If, in an area, the broadcast of a warning message is ongoing and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message with a Message Identifier IE and/or Sequence Number IE that are different from those in the warning message being broadcast, and if the Concurrent Warning Message Indicator IE is not present, the NG-RAN node shall replace the warning message being broadcast with the newly received warning message for that area.
• If an NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message with a warning message identified by the Message Identifier IE and Sequence Number IE, and if no previous warning message has been broadcast in any of the warning areas indicated in the Warning Area List IE, the NG-RAN node shall broadcast the received warning message for those areas.
• If one or more warning messages are being broadcast in an area and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message containing a different Message Identifier IE and/or Sequence Number IE than in any of the currently broadcast warning messages, and a Concurrent Warning Message Indicator IE is present, the NG-RAN node shall arrange for the received warning message to be broadcast in that area.
• If the Concurrent Warning Message Indicator IE is present and a value of "0" is received in the "Requested Number of Broadcasts" IE, the NG-RAN node SHOULD broadcast the received warning message indefinitely until a request to stop broadcasting is received, unless the Repetition Period IE is set to "0".
• If one or more warning messages are already being broadcast in an area and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message containing the Message Identifier IE and Sequence Number IE corresponding to a warning message already being broadcast in that area, the NG-RAN node SHOULD NOT initiate a new broadcast or replace an existing one, but SHOULD still reply by sending a WRITE-REPLACE WARNING RESPONSE message containing the Broadcast Completed Area List IE set based on the ongoing broadcast.
• If the WRITE-REPLACE WARNING REQUEST message does not include the Warning Area List IE, the NG-RAN node shall broadcast the indicated message in all cells within the NG-RAN node.
• If the WRITE-REPLACE WARNING REQUEST message includes the Warning Type IE, the NG-RAN node shall broadcast the primary notification regardless of the settings of the Repetition Period IE and the Requested Number of Broadcasts IE, and process the primary notification according to TS 36.331 and TS 38.331.
• If the WRITE-REPLACE WARNING REQUEST message includes both the Data Coding Scheme IE and the Warning Message Content IE, the NG-RAN node shall schedule the broadcast of the warning message based on the values ​​of the Repetition Period IE and the Requested Number of Broadcasts IE, and process the warning message according to TS 36.331 and TS 38.331.
• If the Warning Area Coordinates IE is included in the WRITE-REPLACE WARNING REQUEST message, the NG-RAN node shall include this information with the warning message broadcast according to TS 36.331 and TS 38.331.

3. NG-RAN Processing The NG-RAN node acknowledges the WRITE-REPLACE WARNING REQUEST message by sending a WRITE-REPLACE WARNING RESPONSE message to the AMF.

• If the WRITE-REPLACE WARNING RESPONSE message does not contain the Broadcast Completion Area List IE, the AMF shall assume that the broadcast was unsuccessful in all cells within the NG-RAN node.