Question: In a 5G System, when the Network Exposure Function (NEF) receives an MBS User Data Ingest Session Status Notification from the Multicast/Broadcast Service Function (MBSF), how does it notify a previously subscribed Application Function (AF)?
Option 1: By sending a `Nnef_MBSUserDataIngestSession_StatusNotify` request message to the AF using the HTTP POST method, targeting the notification URI provided by the AF.
Option 2: Through a direct MBSF-AF interface, bypassing the NEF for status updates.
Option 3: Utilizing SMS or another non-IP based messaging service to inform the AF of status changes.
Option 4: By initiating a new subscription process with the updated status as part of the initial request.
Explanation: In the context of 5G System architecture, the NEF acts as an intermediary between the MBSF and AF for exposing network capabilities. Upon receiving an MBS User Data Ingest Session Status Notification from the MBSF, the NEF's role is to relay this information to subscribed AFs efficiently. The most appropriate and specified method for this relay, considering the provided context, is through sending a targeted `Nnef_MBSUserDataIngestSession_StatusNotify` request via HTTP POST. This approach ensures direct communication with the interested AF, leveraging the pre-provided notification URI for streamlined updates.