The Development of TCP/IP

Present-day TCP/IP networking represents the synthesis of two developments that began in the 1970s and have subsequently revolutionized the world of computing:

• The Internet

• The local area network

The Internet

TCP/IP's design is a result of its historical role as the protocol system for what was to become the Internet. The Internet, like so many other high-tech developments, grew from research originally performed by the United States Department of Defense. In the late 1960s, Defense Department officials began to notice that the military was accumulating a large and diverse collection of computers. Some of those computers weren't networked, and others were grouped in small, closed networks with incompatible proprietary protocols.

Proprietary, in this case, means that the technology is controlled by a private entity (such as a corporation). That entity might not have any interest in divulging enough information about the protocol so that users can use it to connect to other (rival) network protocols.

Defense officials began to wonder if it would be possible for these disparate computers to share information. Accustomed as they were to considerations of security, the Defense Department reasoned that, if such a network were possible, it would likely become a target for military attack. One of the primary requirements of this new network, therefore, was that it must be decentralized. Critical services must not be concentrated in a few vulnerable failure points. Because every failure point is vulnerable in the age of the missile, they wanted a network with no failure points at all—where a bomb could land on any part of the infrastructure without bringing down the whole network. These visionary soldiers created a network that became known as ARPAnet, named for the Defense Department's Advanced Research Projects Agency (ARPA). The protocol system that supported this interconnectable, decentralized network was the beginning of what we now know as TCP/IP.

A few years later, when the National Science Foundation wanted to build a network to connect research institutions, it adopted ARPAnet's protocol system and began to build what we know as the Internet. As you'll learn later in this book, the original decentralized vision of ARPAnet survives to this day in the design of the TCP/IP protocol system and is a big part of the success of TCP/IP and the Internet.

Two important features of TCP/IP that provide for this decentralized environment are as follows:

• End node verification— The two computers that are actually communicating—called the end nodes because they are at each end of the chain passing the message—are responsible for acknowledging and verifying the transmission. All computers basically operate as equals, and there is no central scheme for overseeing communications.

• Dynamic routing— Nodes are connected through multiple paths, and the routers choose a path for the data based on present conditions. You'll learn more about routing and router paths in later hours.

The Local Area Network (LAN)

As the Internet began to emerge around universities and research institutions, another network concept, the local area network (LAN) was also taking form. LANs developed along with the computer industry and were a response to the need for offices to share computer resources.

Early LAN protocols did not provide Internet access and were designed around proprietary protocol systems. Many did not support routing of any kind. Eventually, some companies began to want a protocol that would connect their incompatible, noncontiguous LANs, and they looked to TCP/IP. As the Internet became more popular, LAN users began to clamor for Internet access, and a variety of solutions began to emerge for getting LAN users connected. Specialized gateways provided the protocol translation necessary for these local networks to reach the Internet. Gradually, LAN software vendors began to provide more complete support for TCP/IP. Recent versions of NetWare, Mac OS, and Windows have continued to expand the role of TCP/IP on local networks. TCP/IP grew up around Unix, and all Unix variants are fluent in TCP/IP. The recent popularity of Unix-based systems such as Linux, BSD, Solaris, and Apple OS X has increased the dominance of TCP/IP in the networking world.

As you'll learn in Hour 3, "The Network Access Layer," the need to accommodate local area networks has caused considerable innovation in the implementation of the hardware-conscious protocols that underlie TCP/IP.