History of Computer Networking and the Internet · Computer Networking Interactive

The Internet began as four computers in 1969, and most of what it is today was decided before the Web existed.

Words you will meet

ARPAnet — the first packet-switched computer network, and the Internet’s direct ancestor.
NCP (Network-Control Protocol) — the ARPAnet’s first host-to-host protocol, before TCP/IP (Transmission Control Protocol / Internet Protocol) .
Internetting — Cerf and Kahn’s word for joining separate networks together.
Flag day — a change every host must make on the same day.
NSFNET (National Science Foundation Network) — the US research backbone that grew into the commercial Internet.
Killer application — an application so useful that people adopt the network for it.

Why this matters

History explains the parts of the Internet that look like mistakes.

Why is security bolted on rather than built in? Because of who was on the network in 1969. Why is there exactly one IP (Internet Protocol) protocol that everything must run? Because of a decision in 1983. Why can nobody simply fix these things? Because a flag day was possible with a few hundred hosts and is impossible with billions.

A note on this page

The book’s only figure here is a photograph of an early packet switch. It is a press photograph and this site does not reproduce it, so every diagram on this page is one we made. They are faithful to the book’s dates and numbers.

Sixty years in five steps

Sixty years, in five steps

1961–1972 · packet switchingstep 1 of 5

Three groups invent packet switching independently. ARPA builds the ARPAnet: four nodes by the end of 1969, about fifteen by 1972. NCP becomes the first host-to-host protocol, and Ray Tomlinson writes the first e-mail program.

Every step adds its era to the same axis, so you can see how much of the Internet was already decided before most people had heard of it.

Read all steps as text

1961–1972 · packet switching — Three groups invent packet switching independently. ARPA builds the ARPAnet: four nodes by the end of 1969, about fifteen by 1972. NCP becomes the first host-to-host protocol, and Ray Tomlinson writes the first e-mail program.
1972–1980 · internetworking — Many separate packet-switched networks appear — ALOHAnet, Telenet, Cyclades, SNA — and none of them can talk to the others. Cerf and Kahn work out how to join networks together and coin the word “internetting”. TCP, UDP and IP are conceptually in place by the end of the decade.
1980–1990 · proliferation — Two hundred hosts become a hundred thousand. BITNET, CSNET and NSFNET link the universities. On 1 January 1983 every ARPAnet host switches to TCP/IP on a single flag day. DNS is invented, and TCP gains congestion control. In France, Minitel puts data networking into homes a decade early.
1990s · the explosion — ARPAnet ceases to exist. NSFNET lifts its ban on commercial traffic in 1991 and is decommissioned in 1995. Tim Berners-Lee invents the Web at CERN between 1989 and 1991. About 200 web servers exist at the end of 1993; by 2000 there are four killer applications and a stock-market bubble that bursts.
2000–today · the new millennium — Broadband to the home, then high-speed wireless everywhere: in 2011 wireless devices outnumber wired ones. Social networks build people-networks on top of the Internet. Content providers build private global networks that bypass the paid tiers, and companies move their computing into the cloud.

1961–1972: inventing packet switching

In the early 1960s the telephone network was the world’s dominant communication network, and it used circuit switching . That was an appropriate choice, because voice travels at a constant rate between sender and receiver.

But computers were becoming important, and timeshared computers had arrived. It was natural to ask how to connect computers so they could be shared among users in different places. The traffic such users generate is bursty. A short period of activity while a command is sent, then a long one of inactivity while the user waits for a reply or thinks about the answer.

Three groups, one idea, no contact

	Leonard KleinrockMIT, 1961–64	Paul BaranRand Institute, 1964	Davies & ScantleburyNPL, England
What they contributed
What motivated them
What followed

Cells marked ⓘ have a reason behind them — click to read it.

The book notes that each was unaware of the others’ work. Packet switching was not so much invented as arrived at.

The work at MIT, Rand and the NPL laid the foundations for today’s Internet. But the Internet also has a long history of building things and demonstrating them. J. C. R. Licklider and Lawrence Roberts, both colleagues of Kleinrock’s at MIT, went on to lead the computer science programme at ARPA (Advanced Research Projects Agency) , later renamed DARPA (Defense Advanced Research Projects Agency) . Roberts published an overall plan for the ARPAnet: the first packet-switched computer network, and a direct ancestor of today’s Internet.

The whole Internet, at the end of 1969

1 hops: UCLA → SRI

Drag any device to rearrange the picture. Hover a link to see its rate, delay and length.

Four nodes. The first packet switch went in at UCLA under Kleinrock’s supervision on Labor Day 1969, and three more followed. Press play to send the first message ever carried: a remote login from UCLA to SRI, which crashed the machine at the far end.

Read this diagram as text

UCLA — wired link — SRI
UCLA — wired link — UC Santa Barbara
SRI — wired link — UC Santa Barbara
SRI — wired link — University of Utah

The first message

Kleinrock recalls the very first use of the network: a remote login from UCLA to SRI. They typed L, then O, then G — and the machine at SRI crashed.

The whole Internet was four nodes at the end of 1969.

By 1972 the ARPAnet had grown to about fifteen nodes, and Robert Kahn gave its first public demonstration. The first host-to-host protocol, the network-control protocol ( NCP (Network-Control Protocol) ), was completed. With an end-to-end protocol available, applications could finally be written — and Ray Tomlinson wrote the first e-mail program in 1972.

1972–1980: joining networks together

The initial ARPAnet was a single closed network. To communicate with a host on it, you had to be attached to it.

Then other packet-switched networks appeared, each on its own:

ALOHAnet, a microwave network linking universities across the Hawaiian islands;
DARPA’s packet-satellite and packet-radio networks;
Telenet, a commercial network built on ARPAnet technology;
Cyclades in France, pioneered by Louis Pouzin;
the time-sharing networks Tymnet and GE Information Services;
IBM’s SNA.

The number of networks was growing, and none of them could talk to the others.

In plain words

The time was ripe for an architecture that could connect networks to each other rather than computers to each other. Vinton Cerf and Robert Kahn did that pioneering work, and coined the word internetting for it.

That is where the “inter” in Internet comes from. The Internet is not a big network. It is a way of joining networks — the point §1.3.3 makes about today’s structure.

Those principles were embodied in TCP (Transmission Control Protocol) — but early TCP was quite different from today’s. It combined reliable in-sequence delivery by end-system retransmission (still part of TCP today) with the forwarding functions that are now performed by IP (Internet Protocol) .

Experimenting with it revealed something important: some applications, packetized voice among them, want an unreliable, non-flow-controlled end-to-end service. That recognition led to separating IP out of TCP, and to developing UDP (User Datagram Protocol) . The three key protocols — TCP, UDP and IP — were conceptually in place by the end of the 1970s.

And, in Hawaii

Meanwhile Norman Abramson was building ALOHAnet, a packet radio network letting multiple remote sites share one broadcast medium — a single radio frequency. The ALOHA protocol was the first multiple-access protocol, and chapter 6 still teaches it.

Metcalfe and Boggs built on Abramson’s work to develop Ethernet for wire-based shared broadcast networks. Their motivation was small and practical: connecting several PCs, printers and shared disks. They were laying the foundation for today’s local networks twenty-five years before the PC revolution.

1980–1990: a proliferation of networks

By the end of the 1970s about two hundred hosts were connected to the ARPAnet. By the end of the 1980s the public Internet would reach a hundred thousand.

Much of that growth came from networks linking universities. BITNET (Because It's Time Network) carried e-mail and file transfers among universities in the US Northeast. CSNET (Computer Science Network) was formed to link researchers who had no access to the ARPAnet. In 1986, NSFNET (National Science Foundation Network) was created to reach NSF-sponsored supercomputing centres, starting at 56 kbps and running at 1.5 Mbps by the end of the decade.

The last flag day

On 1 January 1983, TCP/IP was officially deployed as the ARPAnet’s standard host protocol, replacing NCP. It was a flag day: every host was required to change over on that single day.

Nothing like that is possible now. With a few hundred hosts you can require everybody to switch at once. With billions you cannot, which is why later transitions — IPv6 (Internet Protocol version 6) above all — have taken decades instead of a day.

Two more pieces of today’s Internet arrived in this decade. TCP gained host-based congestion control in the late 1980s. And DNS (Domain Name System) was developed, to map a human-readable name such as gaia.cs.umass.edu onto its 32-bit IP address.

Minitel

Internet history is usually told as an American story. It is worth pausing on the exception.

In the early 1980s the French government launched Minitel, an ambitious plan to bring data networking into every home. It consisted of a public packet-switched network, Minitel servers, and inexpensive terminals with built-in low-speed modems. In 1984 the government gave a free terminal to every French household that wanted one.

At its peak in the mid-1990s Minitel offered more than 20,000 services, from home banking to specialised research databases. It was in a large proportion of French homes ten years before most Americans had heard of the Internet.

The 1990s: the explosion

The decade opened with events that marked the Internet’s coming commercialisation. The ARPAnet ceased to exist. In 1991 NSFNET lifted its restrictions on commercial use, and in 1995 NSFNET itself was decommissioned, with backbone traffic passing to commercial ISPs.

But the main event was the World Wide Web, invented at CERN by Tim Berners-Lee between 1989 and 1991. It built on hypertext ideas from Vannevar Bush in the 1940s and Ted Nelson from the 1960s. Berners-Lee and his colleagues built the four key components: HTML (HyperText Markup Language) , HTTP (HyperText Transfer Protocol) , a web server and a browser.

At the end of 1993 there were about two hundred web servers in the world.

Then Marc Andreessen and others built browsers with graphical interfaces. Andreessen and Jim Clark formed the company that became Netscape. By 1995 students were browsing daily; companies large and small began running web servers and trading online. In 1996 Microsoft started making browsers, beginning the browser war that it won a few years later.

Four killer applications, and where they came from

By the end of the millennium the Internet supported hundreds of applications, four of which were decisive:

E-mail, including attachments and web-accessible mail
The Web, including browsing and Internet commerce
Instant messaging, with contact lists
Peer-to-peer file sharing of MP3s, pioneered by Napster

The book draws attention to the split: the first two came from the research community, the last two from a few young entrepreneurs.

Financially the period from 1995 to 2001 was a roller-coaster. Hundreds of startups went public before they were profitable, and many were valued in the billions without significant revenue. Internet stocks collapsed in 2000–2001 and many startups shut down. A few emerged as lasting winners: Microsoft, Cisco, Yahoo, eBay, Google and Amazon.

2000 to today

Perhaps no other technology has transformed society more in the first two decades of this century than the Internet and the smartphones connected to it. The book highlights five developments.

Broadband to the home — cable, DSL (Digital Subscriber Line) , fibre and now 5G fixed wireless. This set the stage for video: user-generated video, on-demand streaming and multi-person video calls.
High-speed wireless everywhere — not only staying connected while moving, but enabling applications that depend on where you are. In 2011 the number of wireless devices connecting to the Internet passed the number of wired ones.
Online social networks — massive people-networks built on top of the Internet, used heavily for messaging and photo sharing. Through their API (Application Programming Interface) s they became platforms for other applications, including mobile payments and distributed games.
Private networks run by content providers — as §1.3.3 described, they connect globally distributed data centres and bypass the public Internet wherever they can.
The cloud — companies and universities have moved their e-mail, web hosting and applications into it, gaining scalable computing and storage plus access to the provider’s high-performance private network.

Hosts on the Internet, 1969 to today

At 2025 (move the pointer over the plot to read it anywhere):

connected hosts:28.5B (2022)

A logarithmic scale, because the numbers span ten orders of magnitude. On a linear axis the first thirty years would be a flat line lying on top of the horizontal axis. Hover to read any point.

Everyday picture

A city that grew from a village. The oldest streets are narrow and in the wrong places, because they were cart tracks between farms. Nobody would design them that way now, and nobody can move them either, because the whole city was built around them.

Several things in this book are cart tracks: no security by default, exactly one network-layer protocol, addresses that were generous in 1981 and ran out in 2011.

Where the picture breaks: cart tracks were never good. The Internet’s early decisions were mostly excellent, and are still working at a scale a million times larger than they were designed for. They constrain us because they succeeded, not because they failed.

Check yourself

Check yourself — §1.7

0 of 7 answered

1.Why did researchers in the early 1960s look for an alternative to circuit switching?
2.How many research groups invented packet switching, and how did they coordinate?
3.predictLook at the growth chart. Why does it need a logarithmic scale?
Compare the 1969 value with today's.
4.What happened on 1 January 1983?
5.Early versions of TCP did something today's TCP does not. What?
6.The book lists four killer applications by the end of the millennium. Where did they come from?
7.Which of these did the French Minitel achieve?

What to remember

Three groups invented packet switching independently in the 1960s, motivated by the bursty traffic of timeshared computers.
Cerf and Kahn worked out how to join separate networks — internetting — which is where the Internet’s name and shape come from.
1 January 1983 was the TCP/IP flag day. Nothing like it is possible at today’s scale.