Question: In a 3GPP network, when is the "Start of interception with ProSe Remote UE ongoing communication" event triggered, and by which network elements, in the context of ProSe UE-to-NW Relay mobility?
Option 1: Only when a ProSe Remote UE initiates a new connection to a ProSe UE-to-NW Relay, sent by the MME.
Option 2: Exclusively during handover of a ProSe UE-to-NW Relay between two eNodeBs, notified by the source eNodeB.
Option 3: When interception starts for an already connected ProSe Remote UE, or upon S-GW change due to ProSe UE-to-NW Relay mobility, sent by the S-GW and/or new S-GW, and also by the PDN-GW in the initial setup.
Option 4: Whenever a ProSe UE-to-NW Relay's IP address changes, reported by the Home Subscriber Server (HSS).
Explanation: This is correct because the event in question is specifically tied to the initiation of interception for an already connected ProSe Remote UE or when there's a change in the Serving Gateway (S-GW) due to mobility of the ProSe UE-to-NW Relay. Both scenarios involve the S-GW (and the new S-GW in case of a change) and the PDN-GW, as these elements are crucial for managing user plane data and thus, lawful interception. This aligns with 3GPP's focus on ensuring seamless and secure communication handovers within its network architecture.