Question: In a UE operating in dual-registration mode (registered to both 5GS via AMF and EPS via MME), how does the network determine the delivery method for an MT (Mobile Terminated) short message when SMS in EPS uses SMS over SGs?
Option 1: The network always delivers the MT short message via SMS over NAS in 5GS, regardless of the UE's registration status.
Option 2: The network decides based on local policy, potentially delivering the MT short message either via SMS over SGs in EPS or SMS over NAS in 5GS.
Option 3: The UE selects the preferred delivery method (SMS over SGs in EPS or SMS over NAS in 5GS) and informs the network.
Option 4: Delivery is always attempted first via SMS over SGs in EPS, with a switch to SMS over NAS in 5GS only if the UE is not reachable.
Explanation: In dual-registration scenarios where a UE is connected to both 5G System (5GS) and Evolved Packet System (EPS), the network's decision for delivering an MT short message can be based on internal policies, allowing flexibility in choosing between SMS over SGs (for EPS) and SMS over NAS (for 5GS). This approach enables the network to adapt to various operational conditions, such as UE reachability, without being locked into a single method.