Which protocol is capable of retransmitting lost packets?

Transmission Control Protocol (TCP) is the protocol that is capable of retransmitting lost packets. This is a crucial feature that ensures reliable communication over a network. TCP works by establishing a connection between sender and receiver, allowing it to track sent packets and their acknowledgments. When a packet is sent, TCP expects to receive a confirmation (an acknowledgment) from the recipient that the packet was successfully received. If the sender does not receive this acknowledgment within a specified timeframe, TCP automatically retransmits the packet.

This reliability mechanism is essential for applications where data integrity is critical, such as web browsing, file transfers, and email.

In contrast, User Datagram Protocol (UDP) does not have built-in mechanisms for packet retransmission or error checking; it sends packets without guaranteeing delivery, which makes it faster but less reliable. File Transfer Protocol (FTP) and Hypertext Transfer Protocol (HTTP) operate on top of TCP, utilizing its reliability features to ensure data is transmitted accurately, but they are not protocols that directly handle packet retransmissions themselves. Thus, TCP's capability to retransmit lost packets is the key reason it is the correct answer.