How does the internet move data around the world?

The internet is a network of networks. Data is broken into small packets, each carrying addressing information, and routers pass those packets from network to network until they reach their destination, where they are reassembled. Cables, radio waves and other links carry the data as pulses of light or electricity, and shared protocols let very different machines understand one another. There is no control center; any device that follows the protocols can take part (see [cloudflare.com](https://www.cloudflare.com/learning/network-layer/how-does-the-internet-work/)). [1]

Each packet holds a piece of the data plus a header that tells the receiving machine what to do with it. Routers and switches handle packets independently, a technique called packet switching. This keeps any one connection from occupying the network for long, so many people can share it. Protocols set the rules: Ethernet for devices on one network, IP between networks, TCP for making sure packets arrive in order, and HTTP for formatting web content. Some uses, such as streaming video, often use UDP instead of TCP ([cloudflare.com](https://www.cloudflare.com/learning/network-layer/how-does-the-internet-work/)). [1]

Within a local network, switches use MAC addresses to deliver messages. Between networks, routers use IP addresses, which work like street addresses because a shared prefix identifies a network. A router can therefore hold one forwarding rule for a whole group of addresses instead of tracking every device ([developer.mozilla.org](https://developer.mozilla.org/en-US/docs/Learn_web_development/Howto/Web_mechanics/How_does_the_Internet_work)). Domain names are human-readable aliases for IP addresses, and a DNS lookup translates one into the other. [2]

Packets are not guaranteed to take the same route, arrive in order, arrive at all, or arrive uncorrupted. The system copes by detecting missing or damaged packets and requesting them again ([cs.cmu.edu](https://www.cs.cmu.edu/~15110-s20/slides/week11-3-internet.pdf)). [3]

Pew describes broadband networks in three parts: the backbone of large fiber-optic lines, which is the main path between countries; the middle mile linking the backbone to local areas; and the last mile connecting a local provider to a customer. Speed is set by the slowest link, usually the last mile ([pew.org](https://www.pew.org/en/research-and-analysis/fact-sheets/2022/07/how-does-the-internet-work-and-what-are-the-implications-for-broadband-policy)). [4]

Internet service providers exchange traffic under peering or transit agreements at internet exchange points, large buildings where carriers link their equipment. Content delivery networks keep copies of popular content on servers near users, shortening the trip ([pew.org](https://www.pew.org/en/research-and-analysis/fact-sheets/2022/07/how-does-the-internet-work-and-what-are-the-implications-for-broadband-policy)). The World Bank describes the chain as running from data centers through exchange points, then submarine cables between continents, then national fiber and microwave networks, and finally fixed or mobile connections to users ([wdr2021.worldbank.org](https://wdr2021.worldbank.org/stories/connecting-the-world/)). [4] [5]

Most international traffic travels through fiber-optic cables on the ocean floor ([cs.cmu.edu](https://www.cs.cmu.edu/~15110-s20/slides/week11-3-internet.pdf)). The New York Times reported in 2019 that nearly 750,000 miles of cable connected the continents, and that companies have typically pooled resources on cable projects, though Google was starting to go its own way ([nytimes.com](https://www.nytimes.com/interactive/2019/03/10/technology/internet-cables-oceans.html)). [3] [6]

Because the core is heavily interconnected, a failed router or data center usually just sends traffic another way, though service may slow. The weak point is the local connection: if your provider goes down, you lose access, and governments that shut off national internet access generally do so by controlling the providers or a single entry point ([cs.cmu.edu](https://www.cs.cmu.edu/~15110-s20/slides/week11-3-internet.pdf)). Access also remains uneven; the World Bank reported that over 600 million people lacked internet access in 2018 ([wdr2021.worldbank.org](https://wdr2021.worldbank.org/stories/connecting-the-world/)). [3] [5]