Question: Over which reference point is the transmission of traffic plane events from the Bearer Binding and Event Reporting Function (BBERF) to the Policy and Charging Rules Function (PCRF) typically carried out, when the BBERF is located in a trusted non-3GPP access?
Option 1: Gx Reference Point
Option 2: Rx Reference Point
Option 3: Gxa Reference Point (a variant of Gxx)
Option 4: Sd Reference Point
Explanation: According to the context, when the BBERF is located in a trusted non-3GPP access, the specific variant of the Gxx reference point that applies is Gxa. This reference point is used for the transmission of traffic plane events from the BBERF to the PCRF, among other functions.