Question: In a 5G network, what triggers the increment of the 'Number of attempted MT SMS messages over NAS via 3GPP access' measurement?
Option 1: Successful delivery of an SMS message to a UE, confirmed by a delivery report.
Option 2: Transmission of an NAS message with an indication of SMS transportation from the Access and Mobility Management Function (AMF) to a User Equipment (UE) via 3GPP access.
Option 3: Receipt of an SMS message by the Application Function (AF) from a UE via 3GPP access for forwarding.
Option 4: Establishment of a packet switched traffic session between the UE and the network.
Explanation: This measurement increments when the AMF sends an NAS message indicating SMS transportation to a UE, marking the network's attempt to deliver an MT (Mobile Terminated) SMS via NAS, regardless of the outcome.