TCP/IP

For two computers to communicate over a connection, they need shared rules. Such rules are called protocols: they define how a message is structured and in what order who sends what. TCP/IP is the most important of these rule sets, because practically the entire internet runs on it. The name consists of two parts because two tasks work together. The IP part handles addressing and ensures that data finds its way to the correct device. The TCP part ensures that nothing gets lost along the way and that everything arrives in the correct order.

The common language of all devices

The internet is not a single unified network, but a collection of millions of small networks. Within it are a Windows laptop, an Android phone, a server in a data center, and a Wi-Fi-enabled refrigerator. These devices come from different manufacturers and run entirely different software. Yet they understand each other because they all speak TCP/IP.

That is exactly the historic breakthrough. In the 1970s and 1980s, there were many competing network standards that were incompatible with one another. TCP/IP prevailed because it was openly documented and freely usable by anyone. Nobody had to ask a company for permission to participate.

This has concrete consequences for today’s technology world. New services such as video streaming, online gaming, or AI chatbots did not need to build their own network. They simply run on top of TCP/IP and thereby instantly reach billions of devices. This shared foundation is one reason why digital products can spread so quickly.

Packets, addresses, and acknowledgments

Data is not sent as one large block, but broken down into small pieces. These pieces are called packets. Each packet gets a header section with additional information, similar to an envelope with a sender and recipient address. It contains the IP address of the destination, a sequence of numbers that uniquely identifies a device on the network.

On its way to the destination, a packet travels through many intermediate stops, known as routers. Each router only looks at the destination address and forwards the packet one step further. It does not know the entire route, only the next sensible direction. That is why packets belonging to the same message can travel by different paths and arrive out of order.

This is where TCP comes in. It numbers the packets and sorts them back into the correct order at the receiving end. For every packet that arrives, the receiver sends back an acknowledgment. If none arrives, the sender simply sends the packet again. A helpful image: IP is the mail carrier, TCP is the registered letter with return receipt.

From the Wi-Fi icon to the IPv6 transition

In everyday life, you notice almost nothing of TCP/IP because it works invisibly in the background. It only becomes visible in the settings. When a phone reports that it has not received an IP address, this is exactly the mechanism being referred to. The number sequence 192.168.0.1, used to access the home router, is also an IP address.

In the news, the topic mostly comes up as address scarcity. The old version, IPv4, allows for about 4.3 billion addresses, and these are no longer nearly enough for all devices worldwide. The successor, IPv6, offers so many addresses that they will practically never run out. The transition has been ongoing in parallel for years, which is why many connections today use both versions simultaneously.

A common misconception is that the internet and the World Wide Web are the same thing. The web, with its pages and links, is just one service that runs on top of TCP/IP. Email, video calling, and online gaming use the same foundation but are not part of the web. TCP/IP, then, is not the content, but the transport system underneath it.