Question: Which protocol element is used to notify the network that a Mobile Station (MS: Mobile Equipment and its User Equipment) has sufficient memory to receive one or more Short Messages, with this information being communicated from the MS to the Home Location Register (HLR)?
Option 1: RP-MO-DATA
Option 2: RP-SM-MEMORY-AVAILABLE
Option 3: RP-ALERT-SC
Option 4: RP-ERROR
Explanation: The correct answer is RP-SM-MEMORY-AVAILABLE because, as per the protocol element's definition, it is specifically designed for notifying the network (particularly the HLR) that the MS has memory available to accept one or more short messages. This ensures the network is aware of the MS's capacity to receive new messages, preventing potential message losses due to memory constraints.