Question: In the context of inter-generational mobility, when a new MME (Mobility Management Entity) requests UE (User Equipment) information from an old AMF (Access and Mobility Management Function), what does the AMF perform on the received GUTI (Globally Unique Temporary Identifier) to retrieve the UE context?
Option 1: Directly uses the GUTI as a 5G-GUTI for lookup
Option 2: Concatenates the GUTI with additional identifiers for comparison
Option 3: Performs a reverse mapping to derive the 5G-GUTI for context matching
Option 4: Ignores the GUTI and uses the IMSI (International Mobile Subscriber Identity) directly
Explanation: When an MME attempts to retrieve UE information from an old AMF, the AMF needs to translate the provided GUTI into a format it can use for lookup in its stored contexts, which are likely in 5G-GUTI format. Performing a reverse mapping allows the AMF to correctly identify and match the incoming request with the stored UE context, facilitating seamless handover or information retrieval across different network generations. This process is crucial for maintaining continuity of service as UEs move between areas covered by different types of cellular networks.