Question: In a scenario where a new SGSN attempts to retrieve UE information from an old MME, how does the old MME handle the E-UTRAN <MME Code> during reverse mapping of a GERAN/UTRAN P-TMSI to create a GUTI?
Option 1: It always uses the RAC (Routing Area Code) as the <MME Code>.
Option 2: It sets the <MME Code> based on the UE's current location, using geographical coordinates.
Option 3: For GERAN/UTRAN P-TMSI, it sets the E-UTRAN <MME Code> to either bits 23 to 16 of the P-TMSI (NRI field) or to the GERAN/UTRAN RAC.
Option 4: It ignores the <MME Code> during reverse mapping for GERAN/UTRAN P-TMSIs.
Explanation: During the reverse mapping process from a GERAN/UTRAN P-TMSI to a GUTI, the old MME sets the E-UTRAN <MME Code> to either the NRI field of the P-TMSI (bits 23 to 16) or to the GERAN/UTRAN RAC, ensuring accurate mapping and successful retrieval of the UE context.