Question: What is the purpose of appending the radio bearer identity to the signalling message, even though it is not transmitted with the message?
Option 1: To provide additional encryption for the message.
Option 2: To ensure that different instances of message authentication codes use a unique set of input parameters.
Option 3: To authenticate the sender of the message.
Option 4: To verify the integrity of the message.
Explanation: The radio bearer identity is appended to the signalling message to avoid using the same set of input parameters for different instances of message authentication codes. This ensures that each instance has a unique set of inputs, which is essential for secure message authentication in telecom networks.