Question: What should a GTP entity do when it receives a Request with a mandatory or verifiable conditional Information Element (IE) having a semantically invalid Value?
Option 1: Ignore the IE and continue processing the rest of the message.
Option 2: Discard the entire message and send a response with Cause set to "Invalid Message".
Option 3: Discard the request, log the error, and send a response with Cause set to "Mandatory IE incorrect" together with a type and instance of the offending IE.
Option 4: Notify the upper layer that a message with this sequence number has been received and continue processing.
Explanation: According to the GTP specifications, when a receiver detects a semantically invalid Value in a mandatory or verifiable conditional Information Element (IE) within a Request, it should discard the request, log the error, and send a response with Cause set to "Mandatory IE incorrect" together with a type and instance of the offending IE. This ensures that errors are properly handled and communicated between GTP entities.