What is a Network?

What good are computers if they cannot talk to each other? How do we share information with each other?

A computer network is a group of connected hosts. It's also a group of connected networks, or a network of networks. A host is your laptop, computer, TV, mobile phone, and more. A "local area network" (a LAN) is a collection of those hosts on the same network, hence they're local to each other and in the immediate area. You have a LAN in your home, which is provided by the router your Internet Service Provider (ISP) gave you. Hosts on your LAN are not only able to talk to each other (theoretically speaking), but they're also able to talk to other hosts on other, remote networks using the service your ISP provides you, which is called a Wide Area Network or WAN.

This looks a bit like this:

Your laptop in the bottom left is connected to your local router inside of your home. This is a LAN. You send traffic to your ISP and it eventually routes the information to other networks (other LANs, eventually) so that your request for a particular website can be fulfilled.

So in a nutshell, networking links everything together, so you have to be able to build networks if you're going to build solutions for clients, businesses, or even just yourself at home. This is because a lot of software relies on the networks to gain access to other network connected software like databases and Application Programming Interfaces (APIs).

For example...

You can look at this another way: what good is a database filled with millions of records of useful information if it cannot be accessed by anything? The data is basically useful only to those who can access it, via the local computer it's on.

That's a lot of sad clients! None of them can get their problems solved because the database is inaccessible to them. Without networking, a lot of what we take for granted today would basically be impossible. I'd go as far as saying that there would be more suffering in the world, in fact. And that's why our databases are network-connected: so software written by programmers can access the data over the network, work with it, and put back whatever results it needs to, delivering results to anyone, anywhere, globally...

That's better! Happy clients operating on the data they need thanks to networking.

The Internet

The Internet is a network of networks. Here's a really cool visualisation of the entire Internet (from several years ago) and its public networks and Internet Protocol (IP) addresses:

It's like looking at a nebula in space!

Summary

Networks are a collection of computers that can talk to each other. The Internet is a big network made up of smaller networks, which in turn can be made up of more networks, until eventually you reach a single host/computer. This is why networking is an important topic. Without networking you wouldn't even be reading this book, because you're using a network, several in fact, to access it.

Next

All of this is made possible using protocols, such as TCP, IP, HTTPS, DNS, and (a lot) more. We'll look at protocols next.