Question: In circuit switched multimedia telephony services, what is primarily handled by the call set-up process, typically implemented as a state machine?
Option 1: In-band media negotiation between User Equipment (UE) devices
Option 2: Out-of-band network signaling for media codec selection
Option 3: Real-time transmission of multimedia content over established calls
Option 4: Out-of-band network signalling for the purpose of call control, including initiating, answering, and tearing down calls
Explanation: The correct answer is Option 4 because, according to telecom principles, call set-up processes are fundamentally responsible for managing the signaling that controls the lifecycle of a call (initiating, answering, and terminating) outside of the media transmission path itself, which is what 'out-of-band network signalling for the purpose of call control' refers to. This is crucial in circuit switched multimedia telephony services for efficiently establishing and managing connections without interfering with the media streams.