ARPANET — arpanet.ximg.app

NETWORK TOPOLOGY

SELECT A YEAR TO WATCH THE NETWORK GROW

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TIMELINE OF KEY EVENTS

FROM VISION TO DECOMMISSIONING

1962

The Galactic Vision

J.C.R. Licklider proposes an "Intergalactic Computer Network" at DARPA — a worldwide interconnected set of computers through which anyone could access programs and data from any site. Most thought it was science fiction.

1966

Roberts' Blueprint

Lawrence Roberts publishes the detailed ARPANET plan. He formalizes packet switching as the transmission method — a radical departure from circuit-switched telephone networks.

OCT 29, 1969
The First Message: "LO"
Charley Kline at UCLA sends the first message over ARPANET to SRI. He typed "LOGIN" — the system crashed after "LO". The first internet message was accidentally poetic: "LO".

1971

The @ Symbol — First Email

Ray Tomlinson sends the first email between two machines on ARPANET using the @ symbol to separate user from host. He reportedly couldn't remember what the first message said — "something insignificant."

1973

Going International

First international connections established to University College London (UK) and the Royal Radar Establishment in Norway. ARPANET crosses the Atlantic for the first time.

1974
TCP/IP Published
Vint Cerf and Bob Kahn publish "A Protocol for Packet Network Intercommunication" — defining TCP/IP. This paper becomes the technical foundation for the entire modern Internet.

JAN 1, 1983
Flag Day — TCP/IP Switchover
All hosts on ARPANET simultaneously switch from NCP (Network Control Protocol) to TCP/IP. This cutover, called "Flag Day," marks the birth of the modern Internet protocol stack.

1983

MILNET Splits Off

The military network MILNET splits from ARPANET to handle classified DoD traffic. ARPANET continues as the research network. The split creates two separate but interconnected networks.

1990

ARPANET Decommissioned

On February 28, 1990, ARPANET is formally decommissioned. The Internet — its successor — already carries far more traffic. The experiment that changed the world quietly ends.

1991

The World Wide Web

Tim Berners-Lee at CERN creates the World Wide Web — HTTP, HTML, and the browser — running on top of the Internet that ARPANET built. The network becomes accessible to everyone.

PACKET SWITCHING EXPLAINED

THE REVOLUTIONARY IDEA BEHIND ARPANET

Circuit Switching (Old Telephone)

A

B

C

A dedicated physical path is reserved for the entire call duration. No one else can use that circuit. If any link is cut, the call drops completely. Inefficient — resources are idle when no data is sent.

Packet Switching (ARPANET)

A

IMP

B

Messages are broken into packets. Each packet travels independently, potentially via different routes. IMPs (routers) reassemble them at the destination. If one link fails, packets reroute automatically.

PACKET SWITCHING ANIMATION — "HELLO" SPLIT INTO [HEL] AND [LO], ROUTED SEPARATELY, REASSEMBLED

📦

IMP — Interface Message Processor

The IMP was the original router. Each ARPANET node had a dedicated Honeywell DDP-516 minicomputer (the IMP) that handled all packet routing, error checking, and retransmission. Host computers talked to their local IMP; IMPs talked to each other. When the first four nodes went online in 1969, each had an IMP. BBN Technologies built the IMPs under a $1 million contract — about $8 million in today's dollars. The IMP is the direct ancestor of every router on the Internet today.

THE FIRST MESSAGE

OCTOBER 29, 1969 — 22:30 HOURS

UCLA SDS SIGMA-7 — ARPANET NODE 1 — TTY SESSION

-- ARPANET IMP #1 ONLINE. BBN HONEYWELL DDP-516. --

-- CONNECTING TO NODE 2: SRI INTERNATIONAL, MENLO PARK --

UCLA% ▋

KEY PEOPLE

THE MINDS BEHIND ARPANET AND THE INTERNET

J.C.R. Licklider

The Visionary

Psychologist and computer scientist who first imagined a global computer network in 1962. As DARPA's first head of the Information Processing Techniques Office (IPTO), he funded the research that would become ARPANET. He never built the network himself — he simply convinced everyone it was possible.

1915–1990 · "Intergalactic Computer Network" (1962)

Lawrence Roberts

The Architect

Chief scientist at DARPA's IPTO, Roberts designed ARPANET from the ground up. He was initially reluctant to leave MIT until DARPA applied pressure. He resolved the protocol disputes, managed the IMP contract with BBN, and supervised the network's construction. Without him, ARPANET would not have been built.

1937–2018 · ARPANET Plan published 1966

Vint Cerf

Father of the Internet

Co-designed TCP/IP with Bob Kahn in 1974, providing the protocol that would eventually unify all networks into the modern Internet. Later served as VP at Google. Often called "the Father of the Internet" alongside Kahn. Recipient of the Presidential Medal of Freedom.

Born 1943 · TCP/IP paper co-authored 1974

Bob Kahn

TCP/IP Co-inventor

Engineer at BBN who helped build the original IMPs, then moved to DARPA where he co-invented TCP/IP with Cerf. Kahn's insight was separating the network layer from the application layer — the "open architecture" principle. Also invented the concept of the "open-architecture networking" that allows diverse networks to interconnect.

Born 1938 · TCP/IP paper co-authored 1974

Ray Tomlinson

Inventor of Email

BBN engineer who, in 1971, sent the first email between two ARPANET computers. He chose the @ symbol to separate username from host — a symbol he picked because it wasn't used in names and meant "at" literally. He reportedly couldn't remember what the first email said, calling it "something insignificant."

1941–2016 · First email sent 1971

Tim Berners-Lee

Inventor of the Web

(Built on ARPANET's foundation)

In 1991, while working at CERN, Berners-Lee invented the World Wide Web — HTTP, HTML, and the browser — running on top of the TCP/IP Internet that ARPANET had become. He made the Web freely available without patents, enabling the open internet we know today.

Born 1955 · World Wide Web launched 1991