The Transmission Control Protocol (TCP)
The Transmission Control Protocol works with IP
to provide reliable delivery. It provides a means to ensure that the various
datagrams making up a message are reassembled in the correct order
at their final destination and that any missing datagrams are re-sent
until they are correctly received.
The primary purpose of TCP is to avoid the loss, damage, duplication, delay, or misordering of packets that can occur under IP. When IP forwards datagrams, individual datagrams may or may not arrive, and they probably will not arrive in the order in which they were sent. TCP adds the reliability that IP lacks. Also, security provisions such as limiting user access to certain machines can be implemented through TCP.
TCP provides reliability by using checksums (error detection codes) on the data, sequence numbers in the TCP header, positive acknowledgment of data received, and retransmission of unacknowledged data.
See also: