Which transport protocols can an application use?

• A. TCP only
• B. UDP only
• C. Both TCP and UDP
• D. Neither

Answer: (C)

Applications can choose between two main transport protocols depending on what they need from the connection. TCP is a reliable, connection-oriented protocol that guarantees data arrives in order and without errors, using retransmissions and flow/congestion control. UDP, on the other hand, is a lightweight, connectionless protocol that delivers datagrams with no delivery guarantees, no ordering, and no retransmission, which reduces latency.

Because of these different characteristics, an application can use either TCP or UDP. Use TCP when reliable delivery is essential, such as file transfers or web traffic. Use UDP when low latency is more important than perfect reliability, such as real-time audio/video or online gaming, or when the application implements its own reliability mechanisms on top of UDP. Some systems even combine both approaches for different parts of the service.

So an application can use both TCP and UDP, depending on the specific requirements of the communication.