Question: When a UE (User Equipment) moves from an E-UTRAN to a GERAN/UTRAN, how are the 6 most significant bits of the E-UTRAN <M-TMSI> mapped to the GERAN/UTRAN <P-TMSI> during the GUTI to RAI, P-TMSI, and P-TMSI Signature mapping process?
Option 1: Bits 29 to 24 of the E-UTRAN <M-TMSI> are mapped into bits 23 to 18 of the GERAN/UTRAN <P-TMSI>.
Option 2: Bits 29 to 24 of the E-UTRAN <M-TMSI> are mapped into bits 29 to 24 of the GERAN/UTRAN <P-TMSI>.
Option 3: Bits 15 to 10 of the E-UTRAN <M-TMSI> are mapped into bits 29 to 24 of the GERAN/UTRAN <P-TMSI>.
Option 4: Bits 0 to 5 of the E-UTRAN <M-TMSI> are mapped into bits 29 to 24 of the GERAN/UTRAN <P-TMSI>.
Explanation: According to the specified mapping rules for when a UE transitions from an E-UTRAN to a GERAN/UTRAN, the correct mapping for the 6 bits starting at bit 29 down to bit 24 of the E-UTRAN <M-TMSI> is directly into the corresponding bits (29 to 24) of the GERAN/UTRAN <P-TMSI>. This ensures continuity and accurate identification across different network technologies.