Year 1 - UE - 00 - General IT culture

As its name stands for it a network is a connection. In IT, it refers to the connection between machines. So when two machines are getting in contact with each other we starts to have our first network. Let’s imagine that you would like to share pictures from your computer to your smartphone. The fact to link one with another with a usb cable will create a network.

You may have heard already that the internet is also named the network of networks, let's see what it means by taking a use case.

Use case: understanding the different actors when a website is made accessible

Here are below a non-exhaustive list of the different actors/elements playing a role when accessing to a website (so to say when accessing to a server holding those files composing the website) from an end user perspective:

1. One internet user, the guy in front of her/his computer. A computer means any terminal (desktop, laptop, tablet, video game console, mobile device). In some cases this internet user can be a robot. Not a physical robot like in science fiction movie but a program in charge of following a task a human gave him. In fact search engines are using robots to look at the content of your website.
   
2. A terminal, we just mentioned those. Terminals are the technologies that internet are using to connect to your website.
   
3. A browser, it is a software used in order to browse/visit pages on the internet. For example, Mozilla Firefox is one of them. Browsers are used to interpret the programming lanuagues of the web pages. Without it you would get an unreadable page to look at.
   
4. A internet box, this component is provided by your ISP (Internet Service Provider). This box is here in order to make the link between your computer and the network. Without it you cannot access the internet network. Most of the time you connect your computer to this box in two ways, either through a cable or through wifi. Note though that it is still possible to create a network with two computers if you can find a way to link those two (wifi, cable, bluetooth etc), but you will then be able to access only to what we call a local network. ISPs are companies who are in charge of taking care of the telecommunication cables which are underground and ensuring that those cables are reliable enough in order to bring you what you paid for (internet subscription).
5. Telecommunication cables, you hardly ever see this part as it is "underground". So your internet box has a cable which goes within your walls, which are going to the streets and if sometimes you are lucky, you can see some operators working on those cables.
6. Routers, those cables we mentioned before are reaching places which are calls routers. As their names stand for it, the routers are here in order to indicate the route to the different communications. So everytime you are asking a web page, those routers are here in order to identify which machine on earth is hosting the information you are asking for.
7. Server, the server is the machine hosting the content you are asking for. According to who you are and the request you are making they will send you an answer.

This is for example one cupboard of cables in charge of deciding where the data will flow, I am pretty sure you have seen some of them already in the street.

Internet is a network of computers. And you have to realize that it is not possible to access to all the data located out there.

There are two kinds of machines on the internet:

• Client machines, which represent your machine but in some specific configuration it can also refer to peer machines.
• Server machines: which as their name stand for it, represent machines which are here in order to answer to client needs.

When a client machine ask something to a server machine, this is what we call a request. And as the way machines are communicating between themselves is called HTTP, we often talk about HTTP requests.

To make it simple, when you go on Mozilla Firefox in order to access https://www.wikipedia.org, your browser (let's say you) is performing HTTP requests in order to display this web page on your browser.

In fact you can see within the picture above, the different HTTP requests which are performed between the browser and the server of Wikipedia where the files are hosted.

As you understand the Internet world is working like in the real one. You have a bar, there are some customers (clients) coming, those clients are making some requests to the servers (I want a coffee, I want a tea) and then servers are answering to those demands.

As in the real world, servers can accept or refuse. In the internet world each request has a status. A "200 status" means that the server agree to answer to your request. Typically that's the case if you require to access to a public web page in Wikipedia. But in some others it can refuse, for example if you try to connect to a social network without the right credentials, then in this case it will show you a different status code. The most famous ones are the not found page "status 404" (I want a coffee Americano, we don't serve them), or server error "status 500" (the server cannot give you this dring because he just broke his leg).

Note that every machine on the internet is identified by a number named: IP address. As it is not very instinctive to access websites based on their IP addresses, one invented the concept of domain names which are understandable names to access a service or a website. In order to make this magic happened this conversion is possible thanks to what we call DNS, a directory which redirect the domain name to the right IP.

Internet is a way to access machines. Those machines are either peers machines or server machines or even any connected machines (like a printer connected to the internet). As you can imagine many people and organizations do not want their machines to be accessible by anyone or robots except themselves. So do not expect to find tools out there to give you the possibility to access to all of them. So as in the real world it may be easy to access to well known cities as there are main roads to go to. But when it is about accessing to a well secure chalet hidden in the mountains then few people can access it.

What is the difference between internet and the web?

The internet is the network, the web is just one part of it. It is the "public" part. The one we are using everyday. But there are other uses of the internet. For example, people are using emails to communicate. Emails are not using HTTP requests to communicate but another protocal called SMTP. When files are transfered most of the time it is by using what we call the FTP, File Transfer Protocol.

Those nice words were here in order to explain the following things, you have what we call:

• Surface web: this is the most visible part of the web. The one that everybody can easily access thanks to popularity and general search engines.
• Deep web: this part of the web is accessible but requires advanced search techniques.
  
• Dark web: the dark web is accessible thanks to a special browser named TOR. Thanks to this technology you can access to some websites that owners of those websites put some restrictions on.
• Rest of the web: only the people who have the right keys (login, password and other security mecanisms) can access it. As you can imagine this part of the web is the biggest one.