TCP is a transport protocol that provides a reliable mechanism for delivering packets between hosts on an internet. TCP takes a stream of data, breaks it into datagrams, sends each one individually using Internet Protocol (IP), and reassembles the datagrams at the destination node. If any datagrams are lost or damaged during transmission, TCP detects this and resends the missing datagrams. The received data stream is a reliable copy of the transmitted data stream.
Note: The PUSH flag is a notification from the sender to the receiver for the receiver to pass all the data that it has to the receiving process. This data consists of whatever is in the segment with the PUSH flag, along with any other data the receiving TCP has collected for the receiving process. Our TCP implementation automatically sets the PUSH flag if the data in the segment being sent empties the send buffer. In addition, our implementation ignores a received PUSH flag because we don't delay the delivery of the received data to the application.
You can use TCP sockets for both passive (server) and active (client) applications. While some calls are necessary for both types, some are role-specific. TCP is the default protocol for stream sockets in the internet domain. For sample C socket communication client and server programs, see the TCP/IP samples included in the OS/2 Warp Toolkit.
TCP is a connection-oriented protocol. It is used to communicate between pairs of applications. After you make a connection, it exists until you close the socket. During the connection, data is either delivered or an error code is returned by networking services.