Which protocol guarantees the reliability of files received by the network's end user?

The Transmission Control Protocol (TCP) is designed specifically to ensure reliable data transmission over a network. It achieves reliability through several mechanisms, including error detection, data retransmission, and the establishment of a connection between the sender and receiver before any data is transmitted. This means that TCP ensures that all packets sent are received correctly and in the right order, and if any packets are lost or corrupted during transmission, TCP will request them to be resent.

In contrast, the other options do not provide the same level of reliability.

File Transfer Protocol (FTP) is focused on transferring files but does not inherently guarantee the reliability of the transfer in the same way TCP does. It relies on TCP for the actual transmission, but the question asks about a protocol that offers reliability directly.

Hypertext Transfer Protocol (HTTP) is used for transmitting web pages and while it can be built on top of TCP for reliable communication, it itself does not manage reliability aspects as a fundamental characteristic.

Simple Mail Transfer Protocol (SMTP) is used for sending emails but, like HTTP, it does not guarantee delivery in the way TCP does. SMTP only specifies how messages are sent and does not provide automatic retransmission in case of delivery failure.

Thus, TCP is the protocol that fundamentally ensures that