Question: Over 3GPP's Sp reference point, when a Policy and Charging Rules Function (PCRF) requests subscription information based on an IMSI as the subscriber ID, what additional identifier is typically included?
Option 1: MSISDN (Mobile Station International Subscriber Directory Number)
Option 2: IMEI (International Mobile Equipment Identity)
Option 3: APN-AMBR (Access Point Name - Aggregate Maximum Bit Rate)
Option 4: NSWO-APN (Non-Standalone Wireless Offload Access Point Name)
Explanation: According to policy and charging control convergence principles, when the subscriber ID used is an IMSI, the PDN identifier accompanying it in Sp reference point requests is specifically defined as the NSWO-APN, crucial for identifying relevant subscription information in mobile network offload scenarios.