and reliable transport (TCP/IP), the program has developed methods for providing electronic mail, remote login, file transfer and similar functions between differing computers over dissimilar networks [4,3]. Today, using that technology, thousands of computers are able to communicate with each other over a "virtual network" of approximately 200 networks using a common set of protocols. The concepts developed are being used in the reference model and protocols of the Open Systems Interconnection model being developed by the International Standards Organization (ISO) [17].
This is becoming even more important with the widespread use of local area networks. As institutions install their own networks, and need to establish communications with computers at other sites, it is important to have a common set of protocols and a means for interconnecting the local networks to wide area networks.
Internet Model
The DARPA Internet system uses a naming and addressing protocol, called the Internet Protocol (IP), to interconnect networks into a single virtual network. Figure 1 shows the interconnection of a variety of networks into the Internet system. The naming and addressing structure allows any computer on any network to address in a uniform manner any computer on any other network. Special processors, called Gateways, are installed at the interfaces between two or more networks and provide both routing amongst the various networks as well as the appropriate translation from internet addresses to the address required for the attached networks. Thus, packets of data can flow between computers on the internet.
Because of the possiblity of packet loss or errors, the Transmission Control Protocol (TCP) is used above the IP to provide for reliability and sequencing. TCP together with IP and the various networks and gateways then provides for reliable and ordered
精品推荐