Question: Under what condition must a new Globally Unique Temporary ID (GUTI) be sent to a User Equipment (UE) in a 3GPP network, ensuring subscriber identity confidentiality?
Option 1: After every successful Service Request procedure
Option 2: Immediately upon UE's initial attachment to the network
Option 3: Only after a successful activation of Non-Access Stratum (NAS) security
Option 4: When the MME (Mobility Management Entity) detects a change in the UE's location area
Explanation: To maintain subscriber identity confidentiality and ensure secure communication, a new GUTI is allocated to a UE only after the NAS security activation is successful. This step guarantees that the new identifier is encrypted and protected from potential eavesdropping or misuse, aligning with the principles of identity confidentiality in 3GPP networks.