Playing a ring back tone is normally the duty of the User Agent, though there are some usage cases for the Atomic platform to play it from its side. The feature could also be used in the case of the caller's User Agent is misconfigured or outdated and is unable to play a ring back tone to the caller.
You can toggle this setting in the Advanced Setting section of the Service Settings.
With Generate Ring Back Tone enabled, the Atomic platform plays a ring tone to the Caller when the call is in a provisioning state, case being a 180/183 has been received from the end carrier, up to receiving and processing 200 OK from the carrier.
Supported Coded formats supported by this feature:-
g711u
g711a
g723
g729
GSM