What is the main function of the transport layer?

Correct answer: Process-to-process message delivery. Explanation: The transport layer provides end-to-end (process-to-process) communication between applications running on different hosts. It directs data to the appropriate application process using port numbers and offers functions such as segmentation and reassembly, optional reliability (for example TCP's acknowledgments and retransmissions), flow control, and basic error detection. Segmentation and reassembly: splits large messages into segments and reassembles them at the receiver.