Question: What is the primary condition for a network-initiated service change request to be counted in the 'Successful network initiated service change requests from CS multimedia to speech' measurement?
Option 1: Receipt of a 'SETUP' message from the UE with a request for speech.
Option 2: Successful completion of a voice call after the service change.
Option 3: Modification of the bearer capability to support only CS multimedia.
Option 4: Reception of a 'MODIFY COMPLETE' message with a speech Bearer Capability IE (BCIE) in response to a network-initiated MODIFY message.
Explanation: This option is correct because, for a service change request to be considered successful under this measurement, the network must receive confirmation of the modification with the new bearer capability set to speech via a 'MODIFY COMPLETE' message, ensuring the change from CS multimedia to speech was successfully initiated by the network and acknowledged by the UE.