Question: What triggers the Short Message Service Center (SC) to initiate a delivery attempt procedure for queued messages destined for a specific Mobile Station (MS), as per the Alert-SC service element?
Option 1: Receipt of a new short message from the MS, indicating its readiness to receive messages.
Option 2: Notification from the Public Land Mobile Network (PLMN) via Alert-SC that the previously unreachable MS has resumed operation or has newly available memory.
Option 3: Expiration of a predetermined time interval since the last failed delivery attempt to the MS.
Option 4: Update of the MS's location in the Home Location Register (HLR), without explicit indication of readiness.
Explanation: The Alert-SC service element informs the SC when an MS, previously unable to receive messages due to unreachability or memory capacity issues, becomes ready again. This is triggered by the PLMN recognizing the MS has resumed operation (e.g., responded to a paging request) or has newly available memory, indicating it can now receive short messages.