Question: What is the primary purpose of the MSISDN Information Element (IE) in the context of UTRAN's Iu interface RANAP signalling?
Option 1: To authenticate User Equipment (UE) during initial network attachment.
Option 2: To prioritize Quality of Service (QoS) for voice calls over data sessions.
Option 3: To manage handover decisions between different Radio Access Technologies (RATs).
Option 4: To indicate the primary Mobile Subscriber Integrated Services Digital Network Number (MSISDN) for Single IP Tunnel (SIPTO) handling at the Iu-PS function.
Explanation: The correct answer highlights the specific role of MSISDN IE in identifying the subscriber's primary MSISDN, crucial for proper SIPTO handling at the Iu-PS function, ensuring seamless and correctly routed packet services. The other options describe unrelated procedures: UE authentication, QoS prioritization, and handover management.