Question: What is the primary function of the Mobility Management Entity (MME) in relation to UE Reachability in ECM-IDLE state?
Option 1: The MME is responsible for executing paging retransmission and optionally Paging Policy Differentiation.
Option 2: The MME is responsible for mapping from UE location to time zone, but not for UE Reachability procedures.
Option 3: The MME is only involved in NAS signalling security and does not handle UE Reachability.
Option 4: The MME is solely responsible for Inter CN node signalling for mobility between 3GPP access networks.
Explanation: According to the provided text, one of the MME functions includes "UE Reachability in ECM-IDLE state (including control, execution of paging retransmission and optionally Paging Policy Differentiation)". This indicates that the primary function of the MME in relation to UE Reachability is indeed executing paging retransmission and optionally Paging Policy Differentiation.