TCP/IP is a name representing a larger suite of network protocols. Some network protocols maintain a constant connection, whereas others do not.
The Internet Protocol is the fundamental building block of the Internet. It is used by other protocols.
This connectionless messaging protocol uses IP. It is used for flow control, detection of unreachable destinations, redirecting routes, and checking remote hosts (the ping utility).
The User Datagram Protocol is a connectionless transport agent. It is used by applications such as DNS and NFS.
The Transmission Control Protocol is a connection-oriented transport agent. It is used by applications such as FTP and Telnet.
The Point-to-Point Protocol is used over serial lines, including modems.