Question: Upon receiving a call set-up request, what action does a UE (User Equipment) take if it cannot support the requested call type or receives incomplete information?
Option 1: The UE automatically rejects the call and sends a "call failed" alert to the user.
Option 2: The UE replies to the network with an alternative set of parameters, if possible, indicating the differences from the original proposal.
Option 3: The UE ignores the request and waits for a repeated call set-up attempt from the network.
Option 4: The UE directly terminates the call attempt without notifying the network.
Explanation: This is because, according to the principles outlined for circuit telecommunication services in a PLMN (Public Land Mobile Network), if a UE cannot support the requested call type or receives incomplete information, it should propose an alternative set of parameters back to the network, provided this action is not restricted by other technical specifications and is feasible. This allows for potential negotiation towards establishing a viable connection, rather than immediate rejection or termination.