How does the internet actually get to your phone? Packets, routers and undersea cables

TUREFF• •0

You tap a link and, a moment later, a page appears that might be stored on a computer on the other side of the world. It feels like magic, but it is really a chain of fairly simple ideas repeated at enormous scale. This guide follows a request from your phone to a website and back again.

Step one: finding the address

Websites have names people can remember, but computers find each other using numbers called IP addresses.

The Domain Name System, or DNS, works like the internet's phone book. Your phone asks a DNS server which IP address belongs to the name you typed.
The answer is often cached, saved nearby for a while, so looking up a popular site is usually almost instant.

Step two: chopping things into packets

Information on the internet does not travel as one long stream. It is broken into small chunks called packets.

Each packet carries a label with where it came from, where it is going and its place in the sequence, rather like numbered envelopes.
Packets can take different routes and arrive out of order. Your phone reassembles them in the right order.
If one goes missing, the receiving end notices the gap and asks for it again. This is why a web page usually arrives complete even over a shaky connection.

Step three: the first hop from your phone

On Wi-Fi, your phone sends radio signals to your home router, which connects through your broadband line to your internet provider.
On mobile data, it talks by radio to the nearest phone mast. From there, the signal usually travels over cables, very often fibre optic, into your mobile operator's network.

Either way, the wireless part is usually only the first short stretch. Most of the journey is through cables.

Step four: routers pass it along

The internet is a network of networks, owned by many different companies, connected together.

Routers are computers whose job is to read each packet's destination and send it one step closer, a bit like sorting offices passing a letter between them.
No single router knows the whole route. Each knows which neighbour is a good next step, and they constantly share information about which paths are working.
If a link fails, traffic can be steered around it, which is part of why the internet is so resilient.

Step five: crossing oceans

If the website lives on another continent, your packets almost certainly cross the sea on the seabed, not through space.

Undersea cables contain strands of glass fibre that carry data as pulses of light. Hundreds of cable systems link the continents.
Satellites carry only a small share of traffic between continents. Cables can carry vastly more data with less delay.
Repairs happen at sea, using specialist ships that lift a damaged section to the surface, mend it and lower it back.

Step six: the server answers

The website's server receives your request and sends back the page, again as packets, along whatever routes are best at that moment.

Big services keep copies close to you. Content delivery networks store popular pages, images and videos on servers in many cities, so your request may not need to cross an ocean at all.
Your connection is usually encrypted. The padlock in your browser means the content is scrambled so routers along the way can pass packets on but cannot read what is inside them.

Why it sometimes feels slow

Distance adds delay, because even light in glass takes time to cross the planet.
Congestion, when many people share the same link, can hold packets up.
Weak signal on Wi-Fi or mobile is the most common bottleneck, and moving closer to the router or a window often helps more than anything else.

Have a question about how your connection works? Ask it in the comments.