History of CN

The World Before Networks Existed

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To understand how computer networks were born, you first have to understand the problem they were trying to solve. And for that, you need to go back to the 1950s when computers were not personal, not portable, and definitely not something a student like you could afford or even access.

In those days, there was one type of computer, that dominated everything the Mainframe.

Mainframes – The Giants

Imagine a computer the size of an entire room. No keyboard on your desk. No screen in front of you. Just a massive, expensive machine sometimes costing more than a building. Those mainframes sat in an air-conditioned room, managed by a team of trained operators, and used by an entire organization.

The way people worked with Mainframes was completely different from how we use computers today. You did not interact with the machine directly. Instead, you punched your program on paper cards called punch cards and submitted them to the operator, and waited. Sometimes hours or sometimes the next day. The operator fed your cards into the machine, it ran your program in a batch (meaning one job at a time, no interruptions), and you got a printed result. This was called batch processing.

Companies like IBM built these machines in the 1950s and 1960s.

But here was the big limitation. These Mainframes could not talk to each other. If UCLA University had a Mainframe and SRI University had a Mainframe, there was no way for them to share data.
If a researcher at UCLA wrote a program and wanted to send it to SRI, they literally had to write it down on paper or post it in the mail. The idea of one computer communicating with another computer electronically across cities, across states did not exist yet.

That gap is where the story of computer networking begins.

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Advanced Research Projects Agency (ARPA)

By the mid-1960s, a man named J.C.R. Licklider at ARPA invented a system where anyone, anywhere, could access programs and data from any computer in the network.

The key technical problem was how do you send data reliably across a long-distance connection? If you use a dedicated telephone line between two cities, that line is occupied for the entire duration of the call. This was called circuit switching, and we will read in the future posts.

A researcher named Paul Baran at RAND Corporation gave a better idea. He suggested that instead of sending data as one large message, the data should be broken into small chunks called packets. Each packet can travel independently through the network, and all packets are reassembled at the destination to get the original message. He called this idea packet switching. Even if some chunks took different routes through the network, they would all arrive and be put back together. This idea was also independently developed by Donald Davies in the UK.

In 1967, ARPA approved the design of a network based on packet switching.

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The Four Universities

ARPANET began with four universities, each chosen because they had strong computer science research programs and were already receiving ARPA funding.

Node 1 – UCLA (University of California, Los Angeles), added in September 1969. UCLA was the first node on the network and served as the Network Measurement Centre.

Node 2 – SRI (Stanford Research Institute, Stanford), added in October 1969. SRI had the Network Information Centre essentially the early version of a telephone directory for the internet.

Node 3 – UCSB (University of California, Santa Barbara), added in November 1969. UCSB worked on interactive mathematics and 3D graphics using the network.

Node 4 – University of Utah, added in December 1969. Utah was famous for its computer graphics research.

The first-ever message sent on ARPANET was from UCLA to SRI, on October 29, 1969, at 10:30 PM. The UCLA team was trying to log in to the SRI computer by typing the command “LOGIN.” They successfully sent the letters “L” and “O” and then the SRI computer crashed. So technically, the first message ever sent on the network that became the Internet was just: “LO.” As if the network itself was saying hello to the world.

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IMP – (The Device That Made It All Possible)

Here is something that most textbooks mention briefly but deserve more explanation. When we say “UCLA was connected to SRI,” we do not mean the Mainframe computers were physically wired to each other directly. In between, there was a special device called the IMP, short for Interface Message Processor.

The IMP was essentially the world’s first router. It was a small, dedicated computer whose only job was to receive packets of data, figure out where they needed to go next, and forward them in the right direction. Each of the four university nodes had its own IMP. The IMPs were connected to each other over leased telephone lines, and the university’s Mainframe computer connected locally to its own IMP.

When UCLA wanted to send a message to SRI, the message went from the UCLA Mainframe to UCLA’s IMP. UCLA’s IMP then forwarded it over the telephone line to SRI’s IMP. SRI’s IMP then delivered it to SRI’s Mainframe. The Mainframes never had to know the details of routing, that was the IMP’s job.

This separation of roles is a principle that survives to this very day. Your phone does not know how to route internet packets. Your router does. The IMP was the ancestor of every router you have ever seen.
On January 1, 1983, a date sometimes called “Flag Day” in networking history, ARPANET officially switched its core protocol to TCP/IP — the same protocol the Internet uses today. That moment is often considered the birthday of the modern Internet.

By 1991, a British scientist named Tim Berners-Lee at CERN invented the World Wide Web, a way of organizing information on the Internet using pages, links, and a browser.

People often confuse the Web with the Internet. They are not the same thing. The Internet is the physical and logical network infrastructure. The Web is one application that runs on top of it.

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Internet vs internet

When you write “internet” (lowercase i), you are referring to any collection of networks that are interconnected. In this sense, your college’s local network connected to your hostel’s Wi-Fi connected to the library’s server forms a small internet.

When you write “Internet” (capital I), you are referring to the specific, global, public network that connects billions of devices around the world, the one you are using to read this, send emails, watch YouTube, and do everything digital.

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How the Internet is Organised – The Hierarchy

It has a layered, hierarchical structure built around the concept of Internet Service Providers, or ISPs. Understanding this hierarchy is essential for understanding how your data actually travels from your phone to a server in America or Japan.

International ISPs – (Tier 1)

These are massive companies like AT&T, Lumen Technologies, NTT, Cogent, Tata Communications that own and operate the physical backbone of the Internet.
Thousands of kilometres of high-speed fibre optic cables, including undersea cables that cross oceans. They connect to each other through peering agreements. Peering agreement is essentially agreeing to exchange traffic for free, because both sides benefit equally. This is called settlement-free peering.

National ISPs – (Tier 2)

They connect to International ISPs and pay for transit, the right to send traffic through the Tier 1 backbone. In India, for example, companies like BSNL, Reliance Jio, and Airtel operate at this level or close to it. A Tier 2 ISP may also peer with other Tier 2 ISPs for efficiency, but it ultimately depends on Tier 1 for reaching all parts of the global Internet.

Local ISPs – (Tier 3)

These ISPs are local access providers. Companies that actually bring internet connectivity to your home, hostel, or college. They buy transit from Tier 2 ISPs and provide it to end users. The connection from your home to the nearest Tier 3 ISP cabinet or exchange point is called the last-mile connection, and it is often the bottleneck in internet speed.

This hierarchy is why the internet has the reliability it does. If your local Tier 3 ISP has a problem then only your area is affected.