ARP Any Subnet Physical information. TCP is not a network layer protocol; it works at the higher lay- ers of the OSI model (transport and above). TCP/IP is the mainstream of the Internet and has been widely adopted as the protocol stack of choice in many Local Area Network (LAN) and Wide Area Network (WAN) arenas. Because of its robustness and capability to deal with the packetization of the data, more organizations are using TCP/IP as their WAN protocol. TCP/IP has its problems, but the advantages far outweigh the disadvan- tages. The industry as a whole and the vendor community in particular has recognized the importance of TCP/IP in the mainstream of products. Just about every LAN Network Operating System (NOS) vendor now supports the use of TCP/IP. From a physical network and data link layer, TCP/IP runs on most any topology. The Internet The Internet is a network of networks. Most people think it is strictly one network, but nothing is farther from the truth. In reality, the Internet is a huge worldwide communications network linking several smaller regional or national networks together into a homogenous network. This network, composed of smaller ones, enables users to quickly access databases and communicate via electronic mail (e-mail). The Internet also connects to Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. X.25, Internets, Intranets, and Extranets Chapter 7 thousands of computers and their data. The data is located in databases at universities, schools, research and development labs, government offices, and commercial enterprises. With access to the Internet from anywhere in the world, you can find, receive, and transmit information on virtually any subject. The Internet provides e-mail and hypertext files, full color graphics, audio, and video services. Many agree that the Internet of today is the Infor- mation Superhighway o