Question: For a UE without ISIM or IMC (for non-3GPP accesses or via SNPN) registering in the IMS, what is the primary purpose of utilizing implicit registration with network assistance?
Option 1: To establish a secure tunnel for media transfer between UEs.
Option 2: To facilitate handover between 3GPP and non-3GPP access networks.
Option 3: To manage QoS (Quality of Service) for IMS sessions.
Option 4: To register at least one Public User Identity for session establishment & IMS signalling.
Explanation: Implicit registration is mandated for UEs lacking ISIM or IMC to ensure they can still engage with the IMS by registering a Public User Identity, crucial for initiating sessions and handling IMS-related signalling. This process leverages network assistance due to the absence of the UE's inherent identity modules.