TCP is a reliable connection-oriented transport service that provides end-to-end reliability, resequencing, and flow control.
Connection-oriented means that a connection is established as the communication begins. During this connection, certain information is exchanged to set the parameters of the communication. End-to-End reliability means that an acknowledgment will be sent back to the sending host throughout the communication to verify receipt of the packets.
As each segment of data is received at the destination, an acknowledgment is sent to the sender within a specified period. - See more at: http://www.certificationkits.com/cisco-certification/Cisco-CCNA-Standard-Internetworking-Models/ccna-the-tcpip-suite.html#sthash.zI5VhE6Z.dpuf