How does the internet actually work?

Science, Nature & Culture · 6 min read

You tap a link and a page appears in under a second, yet the data may have crossed an ocean and passed through a dozen machines on the way. The internet feels like magic, but it is really a very large collection of ordinary cables, computers and agreed-upon rules.

The internet is a network of networks

No single company owns "the internet". It is thousands of separate networks, run by phone companies, universities, governments and businesses, that agree to pass each other's traffic along. Your home Wi-Fi is one tiny network. Your internet provider (Jio, Airtel, BSNL, ACT and so on) runs a bigger one. Those providers connect to still larger carriers, and the carriers connect to each other at meeting points called internet exchanges. The name itself says it: inter-network.

The physical part: cables, mostly

Despite the word "wireless", most of the internet is glass. Data travels as pulses of light through optical fibre, and a large share of international traffic goes through cables lying on the sea floor. These submarine cables are roughly as thick as a garden hose, and India has several landing stations on its coast, including Mumbai and Chennai, where they come ashore. Your phone's mobile signal or Wi-Fi only covers the last stretch, from your device to a nearby tower or router. After that, the data is back on fibre.

Addresses: how machines find each other

Every device on the internet needs an address so replies know where to go. This is the IP address, a string of numbers such as 203.0.113.25 (the older IPv4 style) or a longer one in the newer IPv6 style. IPv4 only allows about 4.3 billion addresses, which is fewer than the number of devices today, so providers often share one public address among many customers, and IPv6 was created to provide a practically unlimited supply.

Humans are bad at remembering numbers, so we use names like wikipedia.org. Something has to translate the name into the number, and that something is DNS.

DNS: the phone book

The Domain Name System is a worldwide directory. When you type a website name, your device asks a DNS resolver, usually run by your provider or a public one such as Google's 8.8.8.8 or Cloudflare's 1.1.1.1. If the resolver does not already know the answer, it works its way down: first the root servers, then the servers for the ending (.org, .in, .com), then the server that handles that specific site. The answer comes back as an IP address and is remembered for a while, which is why a site you visited recently loads its first byte faster.

Handy trick: if one site will not open but others do, the problem is sometimes just your DNS resolver. Switching to a public one in your network settings can fix it.

Packets: sending data in small pieces

A photo or web page is not sent as one lump. It is chopped into small chunks called packets, usually around 1,500 bytes each. Each packet carries the sender's address, the destination address and a sequence number. Routers, the traffic police of the internet, read the destination and pass the packet to the next best router. Different packets from the same page may take different routes and arrive out of order.

The rule book that fixes the chaos is TCP. It numbers packets, the receiver confirms what arrived, missing ones are sent again, and everything is reassembled in the right order. Some things, like video calls and games, prefer speed to perfection and use a lighter protocol (UDP) that does not resend lost pieces; a brief glitch is better than a long delay.

What happens when you open a web page

1. You type an address. Your browser checks whether it already knows the IP address; if not, it asks DNS.
2. A connection is opened. Your device and the server exchange a short greeting (the TCP handshake) to agree they are both ready.
3. Encryption is set up. For addresses beginning with https, the two sides agree on secret keys using TLS, so anyone watching the wire sees only scrambled data. The padlock icon reflects this.
4. The browser asks for the page. This request uses HTTP, the language of the web, and says roughly "please send me the home page".
5. The server replies. It sends back HTML, which describes the structure, and the browser then asks for the images, styles and scripts the page mentions.
6. The browser assembles everything. Text, pictures and layout are painted on your screen, often within a second.

Servers, data centres and CDNs

A server is simply a computer that waits for requests and answers them. Servers live in data centres, which are large buildings full of racks with power backup and heavy cooling. Popular sites do not rely on one building, though. Content delivery networks keep copies of images and videos in many cities, so when you stream a cricket match or a film, the data usually comes from a server fairly near you rather than from another continent. Shorter distance means lower delay, which engineers call latency.

Speed, bandwidth and why things feel slow

Two different things are often confused. Bandwidth is how much data can flow per second, like the width of a pipe, measured in Mbps. Latency is how long a single packet takes to get there and back, measured in milliseconds. A fat pipe with high latency is fine for downloading a big file but annoying for gaming. Slowness can come from weak Wi-Fi signal, a crowded tower, a distant server or an overloaded website, so it is worth testing which one it is before blaming your plan.

Where Wi-Fi, mobile data and the cloud fit in

Wi-Fi is only the link between your device and your router; the router then connects to your provider by fibre or cable. Mobile data does the same job through a tower. "The cloud" is not a mysterious place either. It means other people's servers in data centres, rented out so you do not have to run your own. Your photos backed up to the cloud are just files on those machines.

Who keeps it running?

Standards are agreed by open bodies such as the IETF, which publishes the technical documents behind these protocols. Domain names are coordinated by ICANN, and regional registries hand out IP address blocks. Nobody switches the internet on or off from a central control room, which is also why it is so resilient: if one route fails, traffic usually finds another.

Final thoughts

In short, a name is turned into an address by DNS, your request is split into packets, routers hand those packets across fibre and wireless links, and a server somewhere sends the reply back the same way, all protected by encryption. Once you know these few moving parts, every outage, buffering wheel and padlock icon makes a lot more sense.