The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions. To illustrate further, imagine a world, crossed by multiple cable runs, wires, microwaves, optical fibers, and satellite links. Then imagine a need for data to be transmitted without regard for the condition of any particular node or network. The DoD required reliable data transmission to any destination on the network under any circumstance. The creation of the TCP/IP model helped to solve this difficult design problem. The TCP/IP model has since become the standard on which the Internet is based.

In reading about the layers of the TCP/IP model layers, keep in mind the original intent of the Internet. Remembering the intent will help reduce confusion. The TCP/IP model has four layers: the application layer, transport layer, Internet layer, and the network access layer. Some of the layers in the TCP/IP model have the same name as layers in the OSI model. It is critical not to confuse the layer functions of the two models because the layers include different functions in each model.

The present version of TCP/IP was standardized in September of 1981. As shown in Figure , IPv4 addresses are 32 bits long, written in dotted decimal, and separated by periods. IPv6 addresses are 128 bits long, written in hexadecimal, and separated by colons. Colons separate 16-bit fields. Leading zeros can be omitted in each field as can be seen in the Figure where the field :0003: is written :3:. In 1992 the standardization of a new generation of IP, often called IPng, was supported by the Internet Engineering Task Force (IETF). IPng is now known as IPv6. IPv6 has not gained wide implementation, but it has been released by most vendors of networking equipment and will eventually become the dominant standard.

Web Links History of the Internet http://www.itep.co.ae/itportal/english/ Content/EducationalCenter/ InternetConcepts/ history_future.asp