The Warning Alert and Response Network (WARN) Act was passed by the United States Congress in September 2006 and was signed into law on October 13, 2006, known then as CMAS. CMAS was later renamed as Wireless Emergency Alert (WEA).
The Federal Communication Commission (FCC) released several Report and Order rulings for the Commercial Mobile Alert System. 
As a result of these legislative and regulatory actions the Alliance for Telecommunications Industry Solutions (ATIS) and the Telecommunications Industry Association (TIA) agreed to develop ATIS and TIA standards to support the deployment of CMAS. This standard is listed in Clause 2
The scope of these specifications includes the support of Commercial Mobile Alert System (CMAS) alert message via the GSM/UMTS Cell Broadcast functionality and warning message delivery via E-UTRAN. These specifications covers the mapping of CMAS messages onto the 3GPP-defined Cell Broadcast functionality and warning message delivery functionality, as well as the CMAS application layer functionality from the reception of the CMAS alert message from the Warning Notification Provider to the point of reception by the CMAS capable mobile device.
The CMAS functionality does not require modifications to the 3GPP-defined cell broadcast functionality.
The following functional reference model is based on the diagram from Section III.B.10 of the FCC First Report and Order for the Commercial Mobile Alert System, FCC 08-99 
In addition to the General Requirements specified in Clause 4
, the following requirements are specified for the deployment of CMAS. These CMAS specific requirements are based on the FCC Report and Orders listed in clause 6.1
and further specified in 
Warning Notifications shall support up to 360 characters of GSM 7 bit Default Alphabet 
The following classes of Warning Notifications shall be supported: Presidential, Imminent Threat, Public Safety, Child Abduction Emergency (e.g. AMBER) , and State/Local WEA Test.
When a Presidential Warning Notification is received, it shall always be presented to the user whenever Cell Broadcast Service via GSM/UMTS or warning notification delivery via E-UTRAN is enabled on the UE.
If the Presidential Warning Notification is received in English, then it shall be displayed by the UE. If the Presidential Warning Notification is received in a language other than English, then it shall only be displayed by the UE if the User has selected that language.
A CMAS-capable User Interface (UI) shall support the ability for the user to opt-out of only the Imminent Threat, Public Safety and Child Abduction Emergency Warning Notifications. A CMAS-capable User Interface (UI) shall support the ability for the user to opt-in to the State/Local WEA Test notification.
If the User has opted out of a Warning Notification class, then the Warning Notification for that class shall not be displayed by the UE.
If the User has not opted out of a Warning Notification class, then any Warning Notifications for that class received in English shall be displayed by the UE. This also applies to Warning Notifications received in any additional languages that may be selected by the User.
Warning Notifications may contain URLs and/or phone numbers.
A CMAS-capable User Interface (UI) shall support the ability (e.g., a "click" touch input) for the user to navigate to the URL or initiate a voice call to the phone number which may be included in the Warning Notification 
.The PLMN broadcasting CMAS Warning Notifications shall also broadcast corresponding CMAS Warning Notification Area(s) when the CMAS Warning Notification is required to adhere to the maximum 0,1 of a mile CMAS Warning Notification Area(s) overshooting as specified in 
. This requirement applies only to LTE and NR accesses.
A CMAS-capable UE shall utilize UE-Based Location Calculation 
to determine whether it is located within the corresponding CMAS Warning Notification Area(s) in order to minimize overloading network LCS resources.
Subject to opt-out and opt-in settings described above, a CMAS-capable UE shall present the CMAS Warning Notification sent if there is a corresponding CMAS Warning Notification Area(s) and if it the CMAS-capable UE is able able to determine that its location is within the corresponding CMAS Warning Notification Area(s). Otherwise, if a CMAS-capable UE is unable to or fails to determine its location, the CMAS-capable UE shall present the Warning Notification to the user.
A CMAS-capable UE shall store presented Warning Notifications for at least 24 hours unless explicitly deleted by the user.