Question: In a Circuit Switched (CS) network, what two key messages are used to calculate the mean call set-up time for successful CS network originated calls?
Option 1: IAM message and Ringing message
Option 2: ACM message and REL message
Option 3: Receipt of IAM message and transmission of either ACM or CON message if ACM is not sent
Option 4: Setup message and Connect Acknowledgement message
Explanation: The correct answer, Option 3, accurately reflects the key messages used for calculating mean call set-up time in CS networks. The IAM (Initial Address Message) marks the beginning of the setup process, while the ACM (Address Complete Message) or CON (Connect) message, if ACM is not sent, signifies a successful setup, thus ending the measured interval. This aligns with performance measurement practices in telecom networks for assessing call setup efficiency.