A Brief History of the Internet

Before you can understand how TCP/IP works—or why it works the way it does—you first have to understand the origins of the networking protocols and the history of the Internet. These subjects provide a foundation for understanding the basic design principles behind TCP/IP, which in turn dictate how it is used today.

TCP/IP presented a radical departure from the traditional computer networking services in use during its development. In the early days of commercial computing (the late 1960s), most companies bought a single large system for all of their data processing needs. These systems used proprietary networking architectures and protocols, which primarily consisted of plugging dumb terminals or line printers into an intelligent communications controller, each of which used proprietary networking protocols to communicate with the central hosts.

Most of the early computer networks used this hierarchical design for their proprietary network protocols and services. As users’ computing requirements expanded, they rarely bought a different system from a different vendor, but instead added new components to their existing platforms or replaced the existing system with a newer, larger model. Cross-platform connectivity was essentially unheard of, and was not expected. To this day, you still can’t plug an IBM terminal into a DEC system and expect it to work. The protocols in use by those devices are completely different from each other.

As the use of computers became more critical to national defense, it became clear to the U.S. military in particular that major research centers and institutions needed to be able to share their computing resources cooperatively, allowing research projects and supercomputers to be shared across organizational boundaries. Yet, since each site had different systems (and therefore different networking technologies) that were incompatible with the others, it was not possible for users at one site to use another organization’s computing services easily. Nor could programs easily be ported to run on these different systems, as each of them had different languages, hardware, and network devices.

In an effort to increase the sharing of resources, the Advanced Research Projects Agency (ARPA) of the Department of Defense (DOD) began coordinating the development of a vendor-independent network to tie the major research sites together. The need for a vendor-independent network was the first priority, since each facility used different computers with proprietary networking technology. In 1968, work began on a private packet-switched network, which eventually became known as ARPAnet.

ARPAnet was the world’s first wide-area packet-switching network, designed to allow individual units of data to be routed across the country as independent entities. Previous networks had been circuit-switched, involving dedicated end-to-end connections between two specific sites. In contrast, the ARPAnet allowed organizations to interconnect into a mesh-like topology, allowing data to be sent from one site to another using a variety of different routes. This design was chosen for its resilience and built-in fault-tolerance: if any one organization were bombed or otherwise removed from the network, it wouldn’t affect the rest of the organizations on the network.

During this same time period, other network providers also began interconnecting with the ARPAnet sites, and when these various networks began connecting to each other, the term “Internet” came into use. Over the next few years, more organizations were added to the ARPAnet, while other networks were also being developed, and new network technologies such as Ethernet were beginning to gain popularity as well.

All of this led to the conclusion that networking should be handled at a higher layer than was allowed by the ARPAnet’s packet-switching topology. It became increasingly important to allow for the exchange of data across different physical networks, and this meant moving to a set of networking protocols that could be implemented in software on top of any physical topology, whether that be a packet-switched WAN such as ARPAnet or a local area network (LAN) topology such as Ethernet.

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