How does the internet work? Although many are out and about on the World Wide Web every day, very few can answer this question. In this guide we take a look at the history of the Internet, look at the infrastructure of the global network and explain what goes on in the background when a website is called up.

What is the internet

An explanation of what exactly the Internet is is already in the name. Internet is an Anglicism and the short form of the technical term internetwork . The Latin prefix "inter" means between, in the middle or under, and the English word "network" simply means network in German. The Internet is therefore a network between something, more precisely computers – and for some time now also smartphones, tablets and other smart devices.

The side that requests something on a network is called the client . On the Internet, clients often request data from servers . In contrast to the client, the server only reacts to data requests. In this respect, the client is the active part and the server the passive part. For example, websites, videos or other files are stored on servers. The data that a client requests in a network does not necessarily have to come from a server, but can also come from another client.

The simplest and smallest network consists of only three things: two clients (or client and server) and a cable (or alternatively a wireless connection). You can imagine the Internet in exactly the same way, only a whole corner bigger. The Internet is a network of tens of billions of clients and servers , all of which are connected to one another – keyword "inter". A complex infrastructure is necessary for this. We'll look at what this looks like later. First, take a look at the origins and history of the Internet.

The history of the internet

The first vision of the internet

The first known vision of a worldwide data network goes back to the science fiction author Murray Leinster. In the short story "A Logic Named Joe" he described his vision of the Internet as follows:

"The computer […] distributes ninety-four percent of all television programs, provides all information about weather, air traffic, special offers … and documents every business conversation, every contract … The computers have changed the world. The computers are civilization. [ …] "

The arpanet

The so-called Arpanet (Advanced Research Projects Agency Network) is considered to be the forerunner of the Internet. This went "online" on October 29, 1969 and connected the four mainframes at the University of Utah, University of California at Santa Barbara, University of California and the Stanford Research Institute.

The network allowed computer scientists, scientists, engineers and librarians to exchange files and information both internally within their own university and externally with other universities.

The development of the TCP and IP protocols

In the 1970s, the development of the Arpanet made huge strides. Ray Tomlinson sent the first e-mail in October 1971 and more and more libraries in the US were connected to the Arpanet. A further important milestone placed the computer Cerf and Bob Kahn, the 1974, the Transmission Control Program (TCP), a transmission control program developed.

It enabled overarching communication between different networks. Later, the TCP was divided into a modular architecture: The Internet Protocol (IP) and the Transmission Control Protocol (TCP) . You can find out exactly what these two protocols are for in the section "How does the Internet work".

With the introduction of the Internet Protocol, the name "Internet" slowly established itself for the ever-growing network.

A user-friendly internet for everyone

In the 1980s, the Internet finally became more user-friendly. Thanks to the so-called Domain Name System (DNS) , which was developed in 1984, users no longer had to memorize specific IP addresses from four blocks of digits, but could also connect to the desired computer via fixed URLs.

The Internet slowly spread outside of the academic world . The foundation stone for this was laid by the National Science Foundation, which began in 1986 to network the supercomputers in the USA and thus created the NSFnet . This bridged the gap between academic and private use of the Internet, and the Internet was now slowly spreading outside of the United States. After that everything happened very quickly.

In 1989 the basics of the World Wide Web (WWW) were developed at CERN. Internet providers such as Delphi, AOL and CompuServe began giving US households access to the Internet in 1992, and the first private individuals in Germany went online only a little later. In 1993, Mosaic was the first browser to be able to display the content of the WWW graphically. In 1997, users were able to connect to the Internet wirelessly for the first time via wireless local area networks (WLAN).

The internet today

And today? According to a forecast by Statista from 2019, the number of Internet users worldwide should be 4.14 billion users in 2021. For a long time now, people have not only been online via PCs; today, clients also include smartphones, tablets, smart TVs and other smart devices such as vacuum robots, light bulbs and refrigerators.

Some things have changed: Thanks to 5G , particularly fast cellular connections are now possible, and Starlink is now also used to connect to the Internet via satellite. However, the functioning and basic infrastructure of the Internet have hardly changed.

The infrastructure of the Internet: clients, cables, routers, modems, providers

Router: The traffic cops on the network

As mentioned earlier, the Internet is a network of clients and servers that are all interconnected. With two clients this still works easily with just one cable or a wireless connection. However, the more devices you want to connect to each other, the more complicated the network becomes. If around ten computers are to be connected directly to one another, 45 cables are required. To make things easier, there are routers .

Routers are small computers that make sure that sent and received data reaches the right computers . So you can think of them roughly like traffic cops for data traffic. If we connect our initial ten computers using a router, we only need ten cables – much more efficiently.

Modems: This is how the data gets into the telephone, cable or fiber optic network

In order to enlarge our network, we can now network several networks with additional routers as nodes. However, it would be an enormous effort to connect all routers in the world with network cables. But that is not even necessary, because there is already an infrastructure underground that can be used for networking: telephone, (television) cable and fiber optic lines . In order for your data to be sent and received, however, it must first be made transferable for the respective line. A modem takes care of that.

Modems are either integrated directly in the router or are connected separately to a router. They convert your data so that it can be transmitted via telephone, cable or fiber optic line. They are converted back at the recipient.

Internet service providers and Internet nodes

Thanks to routers and modems, we are now on the move in the telephone, cable or fiber optic network. But how do we get from this network to another now? And how does an email get to the USA from Germany, for example? The Internet Service Providers (ISP) take care of this.

Internet service providers are companies that have special routers and forward the entire data traffic of their network to Internet nodes. This is how data gets from one provider's network to that of another. And this is how the e-mail from Germany comes to the USA.

There are around 340 Internet nodes worldwide (XIPs for "Internet Exchange Points"). These are connected by huge, miles of fiber optic cables under the ground and even under the oceans. The network between the Internet nodes is often referred to as the Internet Backbone . The world's largest commercial Internet node is DE-CIX, which is located in Frankfurt am Main.

How does the internet work?

Now we know which infrastructure is used to get our data from A to B. However, we still don't know how our messages and data are sent back and forth. Two concepts are fundamental to data transmission: packets and protocols .

When data is sent over the Internet, whether as an e-mail, tweet or website, it must first be broken down into small segments, so-called packages. These packets then reach the recipient one after the other via various networks and routers, where they are reassembled into their original form .

The flow of data on the Internet is regulated using several protocols from an Internet protocol family. The most important are Transfer Control Protocol (TCP) and the Internet Protocol (IP) . IP is a system of rules that determines how information is sent from one computer to another over an Internet connection. The so-called IP address determines where the data should go.

The TCP takes care that the packets arrive successfully at the recipient. Its purpose is to ensure that no packets are lost, that the packets are reassembled in the correct order and that there are no delays. If one or more packets are lost (packet loss), the TCP makes a new request to send the missing packets.

This is what happens when you visit a website

Now let's take a quick look at which processes run in the background when you call up a website in the browser. Let's say you want to open the TURN-ON website, you enter "turn-on.de" in the address bar of your browser and press Enter. The following processes are now running:

• Your browser sends a request to your internet provider. This should find out what the IP address of turn-on.de is. Your provider uses a so-called DNS server for this , which works similar to a telephone book. Once it has found the right IP address for the website, it sends it back to your browser via the provider.
• Thanks to the IP address, your browser now knows on which server the TURN-ON website is located. Now your browser makes a request to the target server to send it a copy of the website.
• The server grants the request and divides the website into small packets, which are then sent to your device using TCP / IP.
• Your browser reassembles the individual packages and the website appears on your display.

These processes take place within fractions of a second and the data packets may make a very long journey over many different routers and Internet nodes.

summary

• The Internet is a global network that connects smaller networks and clients and servers with one another.
• The Arpanet, which networked four mainframe computers at American universities in 1969, is considered to be the forerunner of the Internet.
• Data that are sent over the Internet are first converted by a modem for transmission, pass through several routers and Internet nodes and are converted back by a modem at the recipient.
• Before being sent via the Internet, data is first divided into small packets that are then reassembled at the recipient.
• The most important protocols that regulate the flow of data are TCP and IP.
• When accessing a website, a DNS server must first transmit the IP address of the server on which the page is located to the browser. Only then can the browser send a request to the target server, which then sends a copy of the website in small packets to the client via TCP / IP. There the packages are then put together to form the finished website.