Internet

It's the summer holidays and Maria is in Masai Mara National Park in Kenya. She uses her mobile phone to film some elephants near mount Kilimanjaro. Then she uploads the video to her internet page. - Lina must see this. I’ll send the link to her. - Lina is also traveling. She’s staying at a hotel in Barcelona.

She looks at her mobile phone and clicks the link that Maria sent to her. The video from Kilimanjaro appears on her phone. - Wow! Maria is at Kilimanjaro. Oh what cute elephants! - But how did that happen? Well, there's a special cable that goes up Maria’s arm, and .. ..

no. Maria’s WiFi maybe is so good it can reach from Kilimanjaro, because it’s so high, to Barcelona where the air is thinner.. Well.. Maria is in the middle of the savannah. There is no WiFi in the vicinity.

On the other hand, she has a mobile phone account, and she pays for access to the Internet. When she presses ‘upload’, her phone first divides the video into smaller pieces, called packages. Each package contains the address of a computer which stores all of Maria's videos. Maria’s phone sends all these packages to the nearest telephone mast. An underground cable runs from the telephone mast to a special computer called a router.

A router's job is to decide the route that all packages should take. Not all the packages are sent by the same route. But .. it's still the same video. The router tries to choose the fastest route for each package.

If there is a queue of packages one way then it sends them another way, if that’s faster. Finally, all the packages reach this special computer, which stores Maria’s videos, called a server. Once all the packages have arrived, they are reassembled as Maria's elephant video. But how does the video then get to Lina? Lina is sitting in an hotel where there is WiFi connected to the Internet.

When she clicks the link she received from Maria, Lina’s phone sends a package to the same server. This package contains the information that Lina wants to download that video. The video on the server is divided again into many small packages, which each include Lina' s mobile phone address.. .. and which are then sent via underground cables to a router near the server. The router looks at the address in each package, and determines the fastest way to send these packages.

In Lina’s hotel, all the packages are sent via WiFi to her mobile phone. In her phone, the packages are reassembled as the video. Lina can now watch Maria's video from Kilimanjaro. This part is controlled by the hotel’s broadband operator. And this part is controlled by Maria's mobile phone operator.

But here in between, there is a huge number of routers and servers operated by different companies in different countries connected to one single, large network. How do they know how to communicate with each other? Well, there are rules that everyone has decided to follow. These rules, that the entire Internet is built on, are called protocols. Thanks to these protocols, we have a giant network that consists of a variety of cables, underground and undersea, and many computers like routers and servers ... ..which collaborate to stream a huge amount of tiny packages of information around our entire planet.