What is the Internet?

Let us consider a point-to-point communication (for example, computer A to computer B). This communication only requires a means to convey the message: a line, a radio transmission, etc. If a third computer C joins the communication, then we need to increase point to point connections between A and B, A and C, and B and C.

What happens if more and more nodes join the communication network? Imagine the Internet with millions of users. In this case, point-to-point connections become unfeasible. To avoid this problem, intermediate devices come into place, like routers. In this way, Internet users only require a single communication link towards the router, which will be responsible for delivering the message to its final destination.

Thus, the Internet could be seen as a set of “nuts and bolts”.

Internet could be seen as a combination of devices and links interconnecting them. The picture shows a simplified view of the Internet. Close to the final users, we have heterogeneous devices. These are connected to the operator network in a first level. In a second level, the operator network connects its different access in different locations. In a third level, networks from different operators are interconnected, and so on. The further from the final user, the more homogeneous the network is, usually called core network.

Click to enlarge
Figure 1 Internet’s “nuts and bolts” view
Diagram showing how customers connect to ISP's... by Ludovic ferre... from Wikipedia CC BY-SA 3.0

In a simplified view of the Internet, the main components are:

Computing devices:

Communication links:

Forwarders or network devices:

Computing devices:

Hosts = End systems
For example: Your PC, a storage server in the cloud or your neighbour’s smartphone.
Running network applications
For example: Skype, Instagram or, simply, your email inbox.