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5G CMAS Call Flow

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CMAS is a system designed to deliver emergency alerts to mobile devices within a specific geographic area. It is an evolution of the earlier Wireless Emergency Alerts (WEA) system used in 4G/LTE networks. Below is a high-level explanation of the 5G CMAS call flow:

  1. Alert Originator Initiates Alert:
    • The process begins with an authorized alert originator, such as a government agency or authorized public safety entity, initiating an emergency alert.
  2. Alert Message Creation:
    • The alert originator creates an alert message that contains information about the emergency, such as the type of alert, the affected area, and any specific instructions.
  3. Message Distribution:
    • The alert message is sent to the CMAS system, which may involve various components such as alert gateway servers.
  4. Authentication and Validation:
    • The CMAS system authenticates and validates the alert message to ensure it comes from an authorized source.
  5. Service Announcement:
    • The alert message is then distributed to mobile network operators (MNOs) participating in the CMAS system.
  6. Interworking Function (IWF) and Session Management:
    • The MNO's CMAS Interworking Function (IWF) receives the alert message and manages the session for distributing the alert to the targeted devices.
  7. Alert Transmission to Base Stations:
    • The alert message is transmitted from the IWF to the base stations in the affected area. This transmission may use broadcast or multicast mechanisms to efficiently reach a large number of devices simultaneously.
  8. Device Alert Reception:
    • Mobile devices within the specified geographic area receive the alert message. The devices are typically configured to monitor CMAS broadcasts.
  9. Alert Presentation:
    • Once the devices receive the alert, they present the information to the user in a way that is noticeable and attention-grabbing, such as through a loud notification sound, vibration, and a display of the alert message.
  10. User Acknowledgment (Optional):
    • Depending on the implementation, users may be given the option to acknowledge receipt of the alert or to dismiss it.