How data travels through the internet

In the film Rat Race (2001), a billionaire casino owner, as a gamble with his rich friends, decides to get a group of customers at his casino to compete in a road race, travelling across country from Las Vegas to win $2 million which has been deposited in a storage locker in the train station of Silver City, New Mexico. Six coins are hidden in slot machines, and the people who find them get to compete in the race. The rules of the race are simple — the first contestant to the locker gets the prize.

And so a hapless group of six punters, along with their various travelling companions, set out from the casino on their respective journeys, taking various routes and employing modes of transport as diverse as Hitler’s car and a busload of Lucille Ball lookalikes to get to the prize. Each takes a different route, each with the intention of arriving in Silver City before everyone else, and each group find themselves in some very strange places en route.

Leaving aside the unlikely situations which form the film’s comedic core, their journey is similar to that taken by data travelling between computers. This data travels through a network of routers, computers which function to move information forward using a set of rules known as the Internet Protocol (IP), towards your computer.

IP is used to transfer the information about a website stored on a server and being accessed by someone on a computer somewhere else in the world, and by email applications sending email messages between computers. The main function of this protocol is to take information from one computer, with a specific IP address, and move it to a second computer, with another IP address. IP addresses are sequences of four numbers which identify a computer’s location in the world, and function in the same way as phone numbers.

Whether from a website or an email, this information travels in packets — it is broken down into small, discrete fragments of data. These packets then travel across the worldwide network of IP routers. When a packet arrives at a router, this router sends it forward to what it judges to be the router which is mostly likely to get the packet to its destination in the shortest amount of time. Not all packets end up at the same routers along the way however, as the best router to send it to is not necessarily the next closest router to its destination. What a router does with each packet will depend on criteria such as how busy the network is, and any errors it detects in the network, so each packet can end up taking a different route to its contemporaries.

The main function of the router network is to make sure that all packets that started out at computer 1 end up at the correct destination, namely, computer 2. Like the competitors in Rat Race, it does not matter what route these packets take to their destination, as long as they arrive as quickly as possible. Unlike Rat Race, it does not matter which packet arrives first, or what order they arrive in, as they will be reassembled into the original message on arrival. However they do want to arrive quickly, which is what routers aim to do by choosing the best route for each packet.

So, if you are accessing a web page which takes a while to load, you are in fact waiting for these packets of data to arrive. Once they all reach their destination — your computer — the web page will be fully loaded. Similarly, if someone sends you an email with several large files attached, it will take longer to arrive at your computer than an email with no attachments, because it takes longer for all the additional packets of data generated by these attachments to make their way across the internet.

This post is adapted from an essay written as part of my coursework for Internet History, Technology and Security.