Question: In a 3GPP network supporting network-initiated resource signalling, what triggers the request for resources when a service is started or modified, assuming the network has taken over responsibility for resource management?
Option 1: UE (User Equipment) initiates the resource request based on service requirements.
Option 2: Network initiates the resource request upon starting or modifying the service.
Option 3: PCRF (Policy and Charging Rules Function) triggers the resource request after authorizing PCC rules.
Option 4: AF (Application Function) requests resources directly from the access network.
Explanation: According to the described architecture, when the network assumes responsibility for resource management in networks supporting network-initiated resource signalling, it actively triggers the request for resources at the commencement or modification of a service. This contrasts with scenarios where the UE retains this responsibility. The correct answer highlights the network's proactive role in managing resources under these specific conditions, impacting how services are provisioned and managed within the telecom network.