Question: What is the primary purpose of the 'Handover Flag' Information Element (IE) in the S1 Application Protocol (S1AP) when set by the E-UTRAN?
Option 1: To immediately forward all buffered data to the new cell upon handover completion.
Option 2: To instruct the Mobility Management Entity (MME) to buffer secondary RAT (Radio Access Technology) data usage reports triggered by handovers.
Option 3: To notify the MME of an impending handover, allowing for preemptive resource allocation.
Option 4: To request the MME to purge all existing session context due to a handover failure.
Explanation: The 'Handover Flag' IE serves as an indicator for the MME to temporarily store (buffer) secondary RAT data usage reports generated by handovers, crucial for managing and reporting data usage accurately across different radio access technologies during handovers.