Question: In a handover scenario, what information does the new MME extract from the GUTI using reverse mapping to retrieve a UE's information (e.g., IMSI) from the old SGSN?
Option 1: RAI (Routing Area Identity), P-TMSI (Packet Temporary Mobile Subscriber Identity), and P-TMSI Signature
Option 2: IMSI (International Mobile Subscriber Identity), APN (Access Point Name), and IP Address
Option 3: UE ID, SGSN ID, and GUTI (Globally Unique Temporary Identifier)
Option 4: TAC (Tracking Area Code), ECGI (E-UTRAN Cell Global Identifier), and CSG ID (Closed Subscriber Group Identity)
Explanation: In the context of a handover, accurately identifying a UE is crucial for seamless service continuation. The new MME uses reverse mapping on the GUTI to extract RAI and P-TMSI, which, along with the P-TMSI Signature from the UE, are sent to the old SGSN. This combination (RAI, P-TMSI, and P-TMSI Signature) is essential for the old SGSN to verify and match against stored values, ensuring correct UE identification for retrieving information like its IMSI, highlighting precise signaling's importance in maintaining service continuity during mobility events.