Question: In a Network Domain Security (NDS) context, how are GTP-C messages distinguished from GTP-U datagrams to apply IPsec protection selectively, as per 3GPP specifications?
Option 1: Through unique UDP port-number assignments for GTP-C and GTP-U, as defined in the relevant technical specification.
Option 2: By analyzing the payload content of each datagram to determine its type (control or user plane).
Option 3: Based on the source IP address, with specific addresses designated for GTP-C traffic.
Option 4: Using a combination of packet size and protocol headers to differentiate between GTP-C and GTP-U.
Explanation: The correct answer is Option 1 because, according to the specifications, GTP-C is assigned a unique UDP port number, allowing IPsec to easily distinguish GTP-C datagrams from other datagrams (like GTP-U) for selective protection based on these port assignments.