Fundamentals · Study deck
Internet History: ARPANET and TCP/IP
ARPANET joined distant machines, but one network was not yet an Internet.
Physics Phoebe is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Trace the Internet's origin: Explain how ARPANET evolved from a Cold War research project into the global Internet
- Identify key pioneers: Describe the contributions of Vint Cerf, Bob Kahn, Tim Berners-Lee, and other Internet architects
- Compare switching paradigms: Differentiate packet switching from circuit switching and explain why packet switching was revolutionary for network resilience
- Map the timeline: Place key Internet milestones in chronological order from the 1960s to the present
Major section
In 60 Seconds
The parts come from different eras, yet one broken hand-off can still make the current service show a plausible old value.
- A protocol is a shared set of rules for exchanging data.
- TCP means a connected byte stream that tracks order and loss.
- A gateway is the device or service that joins two system paths.
Major section
In 60 Seconds (continued)
Firmware is the stored device code and its version.
- Break a link, repeat the record, restart the bridge, and reject a stale result at the receiver.
- This runway does not turn a timeline into a full design review.
- The Internet did not appear as one invention.
Major section
What To Watch For
Packet switching: Messages are split into packets that share links and can route around failures.
- Layering: Link, internet, transport, and application responsibilities stay separate so each layer can evolve.
- The end-to-end principle: The network core forwards packets while reliability, identity, encryption, and application meaning mostly live at the endpoints.
Major section
Minimum Viable Understanding
And the very first message ever sent was supposed to be 'LOGIN' but the computer CRASHED after only two letters — 'LO'!
- So the first Internet message was accidentally 'LO' — like 'Lo and behold!' Pretty funny, right?".
- Light Lucy adds: "The people who built the Internet were really young!
Major section
Minimum Viable Understanding (continued)
Vint Cerf was only 26 when he started working on ARPANET, and the team that sent that first message included a graduate student named Charley Kline who was just 21!".
- It's like sending a puzzle — each piece takes a different road, and they all meet up at the destination and put themselves back together!".
- Bella the Buzzer chimes in: "And now, 55 years later, there are more devices connected to the Internet than there are people on Earth!
- That's what happens when really smart people share really great ideas!".
Major section
The Cold War Seeds (1957-1965)
The Internet wasn't built to share cat videos — it was born from fear.
- When the Soviet Union launched Sputnik in 1957, the United States realized it was falling behind in science and technology.
- This culture of open research and collaboration would become the DNA of the Internet itself.
- Baran's insight was quantitative.
Major section
The Cold War Seeds (1957-1965) (continued)
Packet switching did not merely replace a voice call with a data packet; it changed the geography of resilience.
- President Eisenhower responded by creating ARPA (Advanced Research Projects Agency) in 1958 — a small government agency tasked with making sure America would never be surprised by technological achievement again.
- Those switching centers were physical places, not just boxes in a diagram.
- This circuit was yours alone for the entire call, even during silences.
Major section
The Cold War Seeds (1957-1965) (continued)
The telephone network used circuit switching — when you made a call, a dedicated physical circuit was established from your phone to the other person's phone.
- A map of central-office sites shows how dense the public telephone network had become in cities and suburbs, while long-distance trunk maps show high-capacity routes concentrating traffic between regions.
- The design goal shifted from holding one reserved path through specific offices to letting many packets use available links and route around damaged or congested parts of the network.
- The postal service is far more efficient because one mail truck carries hundreds of letters simultaneously.
Major section
ARPANET: The First Internet (1969-1983)
The first message ever sent over ARPANET was "LO" — an accidental abbreviation that would be poetic only in hindsight.
- The "IMP" (Interface Message Processor) was the ancestor of today's router — a Honeywell DDP-516 minicomputer that weighed 900 pounds and cost $82,200 (about $680,000 in today's money).
Major section
ARPANET: The First Internet (1969-1983) (continued)
This split was crucial.
- That growth is easier to understand as a map than as a slogan.
- In December 1969, ARPANET was a four-node western U.S. Experiment linking UCLA, SRI, UC Santa Barbara, and the University of Utah.
- It meant that different applications could choose different transport protocols.
Major section
ARPANET: The First Internet (1969-1983) (continued)
The original TCP/IP design had to work with the constraints of 1970s hardware.
- By the mid-1970s, the map had spread across research sites, military labs, and international links.
- Vint Cerf and: Bob Kahn are often called the "Fathers of the Internet" for their 1974 paper defining TCP (Transmission Control Protocol).
- An ARPANET IMP had just 12KB of memory — less than a single modern IoT sensor's buffer.
Major section
ARPANET: The First Internet (1969-1983) (continued)
Yet the fundamental protocol design from 1974 still works, scaling from kilobits to terabits per second.
- Their key insight was creating a universal protocol that could connect different types of networks — ARPANET, radio networks, satellite networks — into one seamless "inter-network" (which became shortened to "Internet").
- The maximum packet size was 1,008 bits (126 bytes).
- Today, a standard Ethernet frame carries 1,500 bytes — nearly 12x more data.
Major section
The Internet Is Born (1983-1990)
The true birthday of the Internet is January 1, 1983 — "Flag Day" — when every machine on ARPANET simultaneously switched from the old NCP (Network Control Protocol) to TCP/IP.
- At midnight, NCP stopped working and TCP/IP was the only option.
- Every host on the network had to be ready.
Major section
The Internet Is Born (1983-1990) (continued)
The first.com domain ever registered was symbolics.com on March 15, 1985.
- Buttons reading "I have TCP/IP — ask me how" were distributed at networking conferences.
- For IoT deployments, DNS is not just a convenience.
- BSD Unix includes TCP/IP — making it free and widely available.
Deck summary
Key takeaways
The parts come from different eras, yet one broken hand-off can still make the current service show a plausible old value.
- Firmware is the stored device code and its version.
- Packet switching: Messages are split into packets that share links and can route around failures.
- And the very first message ever sent was supposed to be 'LOGIN' but the computer CRASHED after only two letters — 'LO'!
- Vint Cerf was only 26 when he started working on ARPANET, and the team that sent that first message included a graduate student named Charley Kline who was just 21!".
Retrieval practice
Recall check
Physics Phoebe says: answer from memory, then check your reasoning.
Q1What was the significance of "Flag Day" on January 1, 1983?
Show answer
Answer: C January 1, 1983 is considered the true birthday of the Internet.
Print reference
Answers
Answer key.
- C · January 1, 1983 is considered the true birthday of the Internet.