Which TCP/IP protocol is primarily used for reliable, connection-oriented data transmission, and how does it ensure reliability?

The TCP/IP protocol primarily used for reliable, connection-oriented data transmission is the Transmission Control Protocol (TCP). TCP ensures reliability through several mechanisms. First, it establishes a connection using a three-way handshake before data transmission begins. This handshake involves the client sending a SYN (synchronize) packet, the server responding with a SYN-ACK (synchronize-acknowledge) packet, and the client sending an ACK (acknowledge) packet back to the server. This establishes a reliable channel between the two endpoints. Second, TCP uses sequence numbers to track the order of data packets. Each packet is assigned a sequence number, allowing the receiver to reassemble the data in the correct order, even if packets arrive out of order. Third, TCP implements an acknowledgement mechanism. The receiver sends an ACK packet back to the sender for each packet it successfully receives. If the sender doesn't receive an ACK within a certain timeout period, it retransmits the packet, assuming it was lost or corrupted during transmission. Fourth, TCP uses checksums to detect errors in the data packets. Each packet includes a checksum value calculated from the data. The receiver recalculates the checksum and compares it to the checksum in the packet. If the checksums don't match, the receiver discards the packet, and the sender will eventually retransmit it. Finally, TCP employs flow control mechanisms to prevent the sender from overwhelming the receiver. The receiver advertises its receive window, which indicates how much data it can buffer. The sender must not send more data than the receiver's advertised window size. These mechanisms collectively ensure that data is delivered reliably and in the correct order, making TCP suitable for applications that require guaranteed delivery, such as web browsing (HTTP), email (SMTP), and file transfer (FTP).