Fundamentals · Study deck
Internet History: ARPANET and TCP/IP
ARPANET was an early network linking distant machines.
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
Start With the Decision
ARPANET was an early network linking distant machines.
- Packet switching sends data in separate pieces across a network.
- A protocol is a shared set of rules for exchanging data; TCP/IP is the set of rules that helped networks exchange those pieces.
- ARPANET joined distant machines, but one network was not yet an Internet.
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.
- TCP means a connected byte stream that tracks order and loss.
- A gateway is the device or service that joins two system paths.
- Firmware is the stored device code and its version.
Major section
In 60 Seconds (continued)
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 deeper sections connect open networking, layered communication, the web, mobile systems, and embedded devices to the evidence a current system still needs.
- 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!
- Bella the Buzzer chimes in: "And now, decades later, there are more IoT connections than people on Earth!
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.
- Those switching centers were physical places, not just boxes in a diagram.
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.
- That design insight does not by itself guarantee survival of any particular fraction of node failures.
- Shared failures or correlated paths would lower the real-world result.
Major section
The Cold War Seeds (1957-1965) (continued)
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 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.
- This circuit was yours alone for the entire call, even during silences.
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).
- That growth is easier to understand as a map than as a slogan.
- It meant that different applications could choose different transport protocols.
Major section
ARPANET: The First Internet (1969-1983) (continued)
In December 1969, ARPANET was a four-node western U.S. Experiment linking UCLA, SRI, UC Santa Barbara, and the University of Utah.
- 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).
- This split was crucial.
Major section
ARPANET: The First Internet (1969-1983) (continued)
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").
- Today, IoT devices often use UDP (User Datagram Protocol) instead of TCP because UDP is lighter weight — a choice made possible by this architectural decision from 1978.
- The original TCP/IP design had to work with the constraints of 1970s hardware.
- An early ARPANET IMP had about 12K 16-bit words of memory, not 12 KB.
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.
- Buttons reading "I have TCP/IP — ask me how" were distributed at networking conferences.
- For IoT deployments, DNS is not just a convenience.
Major section
The Internet Is Born (1983-1990) (continued)
Resolver choice, cache TTLs, CNAME chains, and failover records determine how quickly devices recover when cloud endpoints move or regional services fail.
- A resilient design records which names the device resolves, how long it caches answers, what happens when DNS returns NXDOMAIN, and whether provisioning can update endpoint names without reflashing firmware.
- The first.com domain ever registered was symbolics.com on March 15, 1985.
- BSD Unix includes TCP/IP — making it free and widely available.
Deck summary
Key takeaways
ARPANET was an early network linking distant machines.
- The parts come from different eras, yet one broken hand-off can still make the current service show a plausible old value.
- Break a link, repeat the record, restart the bridge, and reject a stale result at the receiver.
- 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'!
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.
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Answers
Answer key.
- C · January 1, 1983 is considered the true birthday of the Internet.