A network protocol is a set of formal rules explaining how software and hardware should interact within a network in order to transmit information. The Internet protocol family is one such group of network protocols. The group is centered on the Internet Protocol (IP). The other members of the Internet protocol family include the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), the Address Resolution Protocol (ARP), the Reverse Address Resolution Protocol (RARP), the Internet Control Message Protocol (ICMP), and the Internet Group Management Protocol (IGMP).
The entire Internet protocol family is popularly referred to as TCP/IP, reflecting the names of the two main protocols. TCP/IP provides service to many different types of host machines connected to heterogeneous networks. These networks may be local area networks (LANs), such as one you might install in a single building, but they may also be wide area networks (WANs), such as those based on the Point-to-Point Protocol (PPP).
TCP/IP was originally developed by the United States Department of Defense (DoD) to run on the ARPANET, a packet-switching wide area network first demonstrated in 1972. The ARPANET later became part of a wide area network known as the DoD Internet, or, for short, the Internet. Today, the Internet consists of many networks including the National Research and Education Network. The Internet is truly international extending into many countries. It also has gateways to several independent networks which may offer a limited range of Internet services.
Many popular texts use the term Internet to describe both the protocol family and the wide area network. This text uses the term TCP/IP to refer to the Internet protocol suite and the term Internet when referring to the network itself.