Transmission Control Protocol. TCP is used to segment a message or a file to be sent over the Internet and to keep track of the correct order of the packets.

The TCP program layer segments the file into packets, numbers the packets, and hands them over to the IP program layer, which then provides the packets with the destination address and forwards them for eventual delivery.

While on the Internet, the packets may travel via different routes as network resources allow. At the receiving end, another TCP program gathers the packets together, and once they all have arrived, it hands the complete file over to the user.

When TCP is used, the connection remains open until the transmission has been fully performed from the sender's end to the receiver.