When the first packet switching networks appeared in the late 1960s and early 1970s, they were isolated systems with their own rules and interfaces. Connecting them was not straightforward. Different networks used different hardware, different packet formats, and different control mechanisms. The early Internet needed a universal language that could bind many independent networks into one shared space. The engineers who solved that problem were Vint Cerf and Bob Kahn.
The collaboration between Cerf and Kahn produced the Transmission Control Protocol and the Internet Protocol, a suite that turned a collection of incompatible networks into a single, functioning internetwork. Their work defined how devices detect errors, manage congestion, provide reliability, and cooperate across vast distances. TCP IP is not just a protocol suite; it is the core logic of the modern Internet.
The challenge of connecting networks
Bob Kahn joined ARPA in the early 1970s after working on the ARPANET’s packet switching experiments. As he began to envision a network of networks, he realized that simply linking different systems together would not work. Each network had its own internal mechanisms. Creating bridges between them would require a unifying set of rules rather than one network dominating the others.
Kahn proposed a new approach based on four principles. Every network would rely on a universal method for addressing. All data streams would be broken into self-contained packets that could be routed independently. Nodes would not need to know the internal structure of the networks they connected to. And reliability would be handled at the endpoints rather than inside the network itself.
These principles became the foundation for TCP.
Creating the protocol
At the time, Vint Cerf was working at Stanford University and had been involved in early ARPANET research. When Kahn shared his design ideas, Cerf joined him to formalise and expand the concept into a full protocol. Together, they produced the first TCP design in 1973.
Their early work combined reliability, flow control, and data management into a single monolithic protocol. Over time, they separated the functionality into two layers. TCP handled connection management, error correction, and data integrity. IP handled addressing and routing across multiple networks. This separation made the system easier to implement, more flexible, and more scalable.
The birth of the Internet Protocol Suite
TCP IP solved the central problem of early networking. It allowed computers on different networks to communicate without requiring those networks to be redesigned. Each network could continue operating with its own internal technologies while relying on TCP IP to communicate externally.
The protocols were based on a simple set of principles:
- Network independence: no network needed to know how another network worked internally.
- End-to-end reliability: the responsibility for detecting and correcting errors was placed on the communicating hosts, not on intermediate routers.
- Universal addressing: IP created a consistent way to identify every device, no matter what type of network it belonged to.
- Datagram flexibility: IP datagrams could traverse different networks and adapt to varied conditions.
These decisions made it possible for the Internet to grow without centralised control.
From experiment to a global standard
TCP IP was first tested on ARPANET and several satellite and radio networks. In 1983, the ARPANET officially switched from the older NCP protocol to TCP IP. This change marked the transition from a research network to the true Internet.
The protocol suite spread quickly through universities, research institutions, military networks, and eventually commercial service providers. Because it was open, robust, and scalable, it became the de facto standard for all global networking.
A lasting legacy
Cerf and Kahn designed a system that could grow, adapt, and support technologies that did not exist yet. Their work allowed the Internet to expand far beyond its origins as an academic and defence experiment. Today, every device connected to the Internet relies on TCP IP.
For their contributions, Cerf and Kahn received many honours, including the Turing Award. More than that, their collaboration shaped the Internet’s core principles. By focusing on openness and interoperability, they made it possible for networks anywhere in the world to become part of a shared global infrastructure.