Question: What does Cause No. 101 indicate in the context of mobile radio interface Layer 3 specification?
Option 1: The message received is compatible with the current protocol state.
Option 2: A STATUS message has been sent to update the call state.
Option 3: A message has been received which is incompatible with the protocol state or a STATUS message indicates an incompatible call state.
Option 4: The protocol state needs to be updated before sending further messages.
Explanation: Cause No. 101 specifically indicates that there's an incompatibility issue, either because a message was received that doesn't align with the current protocol state or due to a STATUS message signaling an incompatible call state.