Question: In an IP Multimedia Subsystem (IMS), what triggers the increment of the 'Answered IM CN originated session establishments' performance measurement counter?
Option 1: Receipt of a SIP_INVITE message by the Application Server (AS)
Option 2: Transmission of a SIP_200_OK response message by the AS, indicating an answered session establishment
Option 3: Failure of a session establishment with a SIP_430 response code
Option 4: Completion of a packet switched traffic session
Explanation: According to IMS performance management principles, the 'Answered IM CN originated session establishments' measurement is incremented when the Application Server (AS) transmits a SIP_200_OK response message. This specific response indicates that an initial SIP_INVITE message has successfully led to an answered session establishment, impacting Quality of Service (QoS) assessments in telecommunications networks.