Question: What indicates a successful outgoing inter RAT handover from MME to SGSN for UMTS or GSM, in terms of message receipt by the MME?
Option 1: Receipt of 'Direct Transfer Request' message with HO access information
Option 2: Receipt of 'Forward Relocation Complete Notification' message from SGSN
Option 3: Sending of 'Relocation Request Acknowledge' to the UE
Option 4: Establishment of a new S1 bearer
Explanation: The correct answer is based on the understanding that for handovers to UMTS or GSM, the receipt by MME of a 'Forward Relocation Complete Notification' message from SGSN signifies a successful outgoing inter RAT handover. This aligns with telecom concepts related to signaling and session management in heterogeneous network environments (e.g., LTE to UMTS/GSM handovers). Option 1 is actually indicative of a handover to CDMA2000, not UMTS or GSM, highlighting the importance of precise message identification in inter-RAT handover scenarios.