In the United States the concept of the Internet was devised about 40 years ago to address the military's need to maintain communications during a national disaster. Since there were no satellite links at that time, there was concern that national defense measures would gravely suffer if one or more of the existing communication channels were destroyed by a terrorist attack.
By this time scientists at some West Coast universities had already wired their computers together as a way of sharing research. This original network was referred to as the ARPANet (Advanced Research Projects Agency Network). It was launched by a team of UCLA engineers and graduate students in in late 1969.
Then seeing the need for a communication system that could withstand damage at numerous points and still function, the military sought the help of the day's computer experts. These experts came up with a plan for modifying their basic ARPANet idea to create a national network -- what we would now call "the Internet."
The military considered the idea and then rejected it as unworkable. Fortunately, the universities went forward on their own.
The professors who originally used their network to link large mainframe university computers soon saw the advantage of accessing this information from their homes and offices via modems. At about the same time, corporations saw advantages in networking computers to share information with employees throughout the country. They then set up their own internal and external networks. Soon, more and more people got into the act -- and, the rest is history.
Up to that point all Internet information was shared only in the form of basic lines of text referred to as ASCII (American Standard Code for Information Interchange) characters. These consist of all the upper and lower case letters of the alphabet, numbers 1-9, plus a dozen or so symbols and special characters. Internet information exchanged at that time primarily centered in e-mail and newsgroups (information exchange and Internet postings among people sharing similar interests).
Specialized newsgroups or user groups eventually grew to 10,000 in number, covering every imaginable topic. Individuals could post newsgroup messages under topic headings and read what everyone else had to say.
Once the GUI (mouse controlled Graphical User Interface) was introduced, it was simply much easier (although not necessarily faster) to use a browser to access Worldwide Web discussion groups and e-mail. Many e-mail programs, such as the free Mozilla Thunderbird and Outlook Express programs, still allow users to log on to these newsgroups.
Internet, Intranet and Extranet
At this point we need to distinguish between some key network terms. A computer network that is internal to an institution is referred to as an intranet. This can be used to send messages between employees or link to a common printer or central storage device.
This type of network typically contains private information: personnel files, sales figures, payroll records, etc. Intranets commonly have layers of accessibility, depending on the user. The company CEO (through his name and password) may have access to all the data; managers another level of data; and employee groups with a lower rank will only be given access to information needed to perform their particular duties. For security reasons the typical intranet cannot be accessed from outside of the organization (although hackers sometimes find a way).
An institutional network that has both internal (intranet) and external (Internet) elements is referred to as an extranet. Because extranets contain private internal information as well as information that is intended for the public, access must be carefully controlled.
Firewalls, use hardware and software to prevent unauthorized access to intranet information. Personal computers should also have software firewalls to block unwarranted access by outside sources. These come as part of the computer's operating system or as part of add-on virus and malware protection.
Clients and Servers
Things have progressed in some major ways since the Internet was launched about 40 years ago. For one thing, the Internet has had to develop a complex structure and organization to deal with millions of users. To look at this aspect of the Internet we'll start with the two basic computer divisions: clients and servers.
Most of the millions of computers that regularly access the Internet are clients; i.e., they primarily seek and display information from the Internet. But there must also be computers that supply this information. These are normally large computers, referred to as servers that store information and make it available to large numbers of clients. (Of course, in the era of music sharing programs, almost any computer can be configured as both a client and a server, but we are looking at the big picture here.)
Since there may be hundreds or even thousands of miles between a client and a server, there has to be an interconnection system that quickly bypasses normal (and relatively inefficient) telephone lines.
Once you contact your Internet service provider (ISP) through any of the high-speed "on-ramps," your computer is routed to a regional or national backbone of the so-called "superhighway."
One of the major U.S. backbone systems is illustrated below. What isn't shown are the tens-of- thousands of high-speed ISP lines and Internet on-ramps. If they were visible, they would appear as a dense and intricate "web" extending in all directions from each of the major switching points (shown as red dots in the illustration).
Once Internet traffic hits one of the backbones it goes by fiber optic cable capable of transmitting from 150 million to 10 trillion bits of data per second.
Other countries have their own "webs." The drawing below illustrates some of the world's major Internet cable routes. Submerged cables handle traffic over water.
And, to make the Internet web even more complex, much of the international Internet traffic now goes by satellites. This concept was discussed in an earlier television module.
In the next module we'll look at the complex systems of "addresses" that are used to route millions of users to their proper destinations.