Which protocol uses only TCP?

The correct answer is HTTP, as this protocol exclusively employs TCP (Transmission Control Protocol) for its communications. HTTP operates over TCP to ensure reliable transmission of data. TCP is a connection-oriented protocol that establishes a connection between the client and server, facilitating the delivery of complete and intact messages while managing the order of packets. This reliability is crucial for web communication, where the correct loading of resources, such as web pages and assets, is dependent on the integrity of the data being transferred.

Although other protocols like Telnet also utilize TCP, they are not the only protocols that do so; Telnet can be seen as an auxiliary protocol for text-based communication over a network. VoIP typically relies on multiple protocols, including both TCP and UDP (User Datagram Protocol), which supports real-time communication. As for DNS, it predominantly operates over UDP for query responses but may use TCP for tasks like zone transfers, showcasing a versatility that is not found in HTTP's exclusive reliance on TCP. Thus, HTTP's specific use of TCP makes it the unique choice in this context.