Question: In a 3GPP System Architecture Evolution (SAE) setup, where is user data confidentiality between the UE and another entity **NOT** defined by 3GPP specifications when using DS-MIPv6?
Option 1: Between the UE and an entity in the Evolved Packet Core
Option 2: Between two entities in a non-3GPP access network
Option 3: Between the UE and the PDN GW for signaling data
Option 4: Between an entity in the non-3GPP access network and the Evolved Packet Core
Explanation: According to the provided context, user data confidentiality between two entities within a non-3GPP access network falls outside the scope of 3GPP specifications. This highlights a boundary in the security architecture where 3GPP's defined security mechanisms do not apply once the communication is confined within a non-3GPP access network's domain.