A Network of Networks
The internet is not a single machine or company. It is a worldwide collection of separate networks, run by internet service providers, universities, companies and governments, that agree to exchange data using shared rules called protocols. The name comes from “internetworking”: connecting networks to each other.
It helps to separate the internet from the World Wide Web. The internet is the underlying system that moves data. The web is one service that runs on it, made of pages linked together and retrieved using a protocol called HTTP. Email, video calls and online games also use the internet but are not part of the web.
Everything Becomes Packets
Whatever you send, whether a message, photo or video, is at bottom a long series of ones and zeros, the same kind of binary code that computers use to store information. Before it travels, that data is chopped into small chunks called packets, each typically up to around a thousand to fifteen hundred bytes.
Each packet carries a header, which is like an envelope. It includes the sender’s address, the destination address, and information that helps put the pieces in order. Splitting data this way has several advantages:
- Many conversations can share the same cables at once, with packets from different users interleaved.
- If one path is busy or broken, packets can take another route.
- If a packet is lost, only that piece needs to be sent again.
Different packets from the same message may take different routes and arrive out of order. The receiving device reassembles them using the sequence information.
Addresses
For packets to arrive, every device needs an address. On the internet this is an IP address. The older format, IPv4, uses four numbers from 0 to 255 separated by dots, such as 192.0.2.1 (a reserved example address). Four such numbers allow about 4.3 billion unique addresses, which turned out not to be enough for the number of devices in the world. A newer format, IPv6, uses much longer addresses and allows a vastly larger number.
Most people never see these numbers because of the Domain Name System, or DNS. Humans prefer names such as a website’s domain, while machines route by number. DNS works like a distributed phone book: when you type a name, your device asks a DNS server to look up the matching IP address. The answer is often remembered for a while so that later lookups are faster.
Home networks add one more detail. Your router usually has one public address and gives each device inside a private one. It keeps track of which internal device made each request so replies go to the right place.
Routers and the Path Across the World
A router is a device that forwards packets toward their destination. It looks at a packet’s destination address and decides which neighboring network is the best next step, using tables built from information exchanged with other routers. No single router knows the whole route. Each makes a local decision, and the packet hops from router to router until it arrives. That journey can cross a dozen or more hops.
Between those hops are physical links. They include copper cables, radio links such as Wi-Fi and mobile networks, satellite links, and above all optical fiber, in which data is carried as pulses of light, a topic related to the science of light. Much of the traffic between continents travels through fiber-optic cables laid on the seabed. Large providers and exchange points connect their networks to one another so that traffic can pass between them.
Servers and Clients
Most internet activity follows a client-server pattern. Your phone or laptop is the client. It asks for something. A server is a computer that stores content or runs a service and responds to requests. Servers are often kept in large data centers with reliable power and fast connections. Many services now run on rented computing power spread across such centers, which is what people mean by cloud computing.
What Happens When You Open a Web Page
Putting the pieces together, a simplified version of a page load goes like this.
- You type a web address or tap a link.
- Your device asks DNS for the IP address matching the domain name.
- It opens a connection to that address, using a protocol called TCP that sets up a reliable exchange and arranges for lost packets to be resent.
- Your browser sends an HTTP request asking for the page.
- The server replies with the page’s code, and your browser may then request images, styles and scripts as separate items.
- The browser assembles all the parts and displays the page.
This usually takes a fraction of a second. Delays come from the distance data must travel, from busy networks, and from slow servers. Light in fiber is fast, but crossing an ocean and back still takes a noticeable number of milliseconds.
Layers and Standards
The internet works because its functions are divided into layers, each doing one job. A rough picture: the lowest layer moves bits over a physical link, the next handles addressing and routing across networks (IP), another provides reliable delivery (TCP), and the top layer holds applications such as the web or email. Each layer relies on the one below and does not need to know how it works. This is why the same web page can arrive over Wi-Fi, a cable or a mobile signal without the website knowing the difference.
Open standards, developed through cooperative bodies and published documents, let equipment from many makers work together. The early research network ARPANET began carrying data in 1969, and the shared TCP/IP rules that tie networks together were adopted in the early 1980s. The web arrived around 1990 and brought the internet to a broad public in the following years.
Privacy and Security Basics
Packets crossing many networks could in principle be read along the way if they are not protected. Most websites now use encrypted connections, so that only the two ends can read the content. The ideas behind this are covered in encryption basics. Encryption protects the contents, but some information, such as which servers you contact, may still be visible to the network operators or the services you use.
The Short Version
The internet is a cooperative system: data is split into packets, labeled with addresses, passed along by routers across many networks, and reassembled at the destination, with servers providing content and DNS translating names into numbers. Its design, which favors simple shared rules over central control, is a large part of why it has been able to grow so far.