Question: What triggers the increment of the 'Number of MSUs received on MTP3/MTP3B signalling link' performance measurement in a Core Network (CN) Circuit Switched (CS) domain?
Option 1: Transmission of a Message Signalling Unit (MSU) on the signalling link.
Option 2: Receipt of a Signal Unit (SU) on the signalling link.
Option 3: On receipt of a Message Signalling Unit (ITU-T Recommendation Q.752).
Option 4: Establishment of a new signalling link set.
Explanation: The measurement increments upon receiving an MSU, highlighting the importance of signalling link traffic monitoring in circuit-switched domains for network performance optimization and troubleshooting.