The Windows Sockets model offers service for both connection-oriented and connectionless protocols. In the TCP/IP protocol family, TCP provides a connection-oriented service, whereas UDP (user datagram protocol) offers connectionless service. In the Windows Sockets model, connection-oriented service is offered by stream sockets, connectionless service is provided by datagram sockets.
TCP is a reliable, connection-oriented protocol, used by applications which either plan to exchange large amounts of data at a time, or by applications which require reliability and sequencing. For example, FTP (file transfer protocol), a protocol which facilitates the binary or ASCII transfer of arbitrarily large files, represents an application written to TCP or stream sockets. In contrast, if an application is willing to manage its own sequencing or reliability, or is using the network for low-bandwidth iterative processing, UDP is often used. An application which keeps system clocks synchronized by periodically broadcasting its system time would probably be written to use UDP.