Question: In a Point-to-Point Short Message Service (SMS) over the mobile radio interface, as per 3GPP specifications, what triggers the SMR entity to enter the "Wait to send RP-ACK" state for a mobile originating short message or notification transfer?
Option 1: Receipt of an RP-ACK from the peer entity and successful transmission of the associated RP-DATA.
Option 2: Passing a received RP-DATA or RP-SMMA message to the Transaction Layer (TL) and setting the timer TR2N.
Option 3: Expiration of the TR2N timer without receiving a response for a previously sent RP-DATA.
Option 4: Initiation of a new mobile terminating short message transfer by the SMR entity.
Explanation: The correct answer, Option 2, accurately describes the condition that triggers the transition into the "Wait to send RP-ACK" state. This is because, as outlined in the specifications, entering this state is contingent upon two actions: successfully passing a received RP-DATA or RP-SMMA message to the Transaction Layer (TL), and initiating the TR2N timer. This state is crucial for ensuring reliable transmission by awaiting the appropriate response (RP-ACK) before proceeding. The other options do not accurately represent the trigger for entering this specific state according to the 3GPP's Point-to-Point SMS support on mobile radio interface specifications.