PERMANENT / PUBLIC EXHIBITION

Internet. From four nodes to a worldwide network.

How packet switching came about, why the modem whistled, where the Web came from, and how an academic experiment became an everyday infrastructure. Safety is an important chapter in this story, not its only content.

Start with the ARPANET Disassemble the modem
internet-museum.local 
> connect --year 1969 nodes: 4 message: LO protocol: NCP > connect --year 1992 --country CS link: CVUT <-> Linz speed: 19.2 kbit/s status: online > users --year 2024 world: 5.80 billion
1969 four ARPANET nodes and the first transmitted message
1992 Czechoslovakia officially joins the Internet
5.80 billion estimate of internet users in the world in 2024

The prehistory of the network

From four computers to billions of people

The Internet was not created by a single invention or in a single day. It is the result of decades of work on packet switching, connecting different networks and open protocols. First he connected research computers, then universities and companies; the public joined in with commercial services and the World Wide Web in the early 1990s.

Internet

A network of networks

A global infrastructure that connects networks using the TCP/IP family of protocols. It carries the web, e-mail, file transfer, voice, video and many other services.

World Wide Web

One service over the internet

Hypertext documents transmitted via HTTP and opened by a browser. Tim Berners-Lee designed the Web at CERN in 1989, two decades after ARPANET.

Who was the "Father of the Internet"?

A more accurate answer is: there were more fathers and predecessors

The title is most often used in the plural for Vint Cerf and Bob Kahn, co-authors of the TCP/IP architecture. However, without the work of other people, there would be nothing to connect.

1962

J.C.R. Licklider

He described the vision of a worldwide computer network and promoted networking research as head of ARPA.

1961–1965

Kleinrock, Baran, Davies

They independently developed the theory of packet networks; Donald Davies coined the term "packet".

1973–1974

Bob Kahn and Vint Cerf

They designed the open architecture of interconnected networks and the protocol that gave rise to TCP and IP.

1969–1980s

Postel, Crocker, Tomlinson and others

RFCs, addressing, protocols, and network email turned the experiment into a usable ecosystem.

1989–1993

Tim Berners-Lee

Invented the Web: URL, HTTP, HTML, first server and browser. He invented the Web, not the Internet.

Milestones

When did a network experiment become a public space

World
  1. ARPANETFour nodes; the first message travels from UCLA to SRI.
  2. E-mailRay Tomlinson and the first network "killer app".
  3. TCPCerf and Kahn publish a protocol for interconnected networks.
  4. TCP/IPARPANET switches to TCP/IP on January 1st.
  5. NSFNETThe academic backbone extends access to researchers.
  6. Companies and the publicNSF opens up the Internet to public and commercial use.
  7. The Web released freelyCERN releases WWW software into the public domain.
  8. Private backboneNSFNET ends; commercial operation is taken over by providers.
Czech Republic / Czech Republic
  1. BITNETCzechoslovakia enters the academic network.
  2. CTU–LinzExperimental connection at 9.6 kbit/s.
  3. Officially onlineThe first Czechoslovak workplace on the Internet, 19.2 kb/s.
  4. CESNETPrague and Brno connected by a 64 kb/s backbone.
  5. Commercial ISPThe first providers for companies and the public are appearing.
  6. Dial-up reaches more homesHouseholds weigh connection fees against metered telephone charges.

Who was joining

The Internet opened up in layers

  1. 01Research and defense1969–1970s

    The first nodes belonged to universities, laboratories and projects funded by the American agency ARPA.

  2. 02Universities1980s

    NSFNET and national academic networks made TCP/IP available to the broader research community.

  3. 03Companieslate 1980s and early 1990s

    Commercial Internet services and private backbones emerged; in 1991, the network opened to ordinary commercial traffic.

  4. 04The public1990s

    Dial-up accounts, graphical browsers, and the Web turned a specialist network into a mass medium.

  5. 05Czech householdsthe second half of the 90s

    After the academic connection and the first ISPs in 1994, the Internet spread over dial-up telephone lines.

Interactive statistics

How many people were online and how fast their connections were

Year2024
World · users5.80 billion
World · speed95 Mbit/s
Czech Republic · users9.56 million
Czech Republic · speed63.4 Mbit/s
Development of the number of Internet users and the speed of fixed connections in the world and in the Czech Republic Two time-aligned line graphs from 1991 to 2025. Users use the left axis and download speed the right logarithmic axis.
World · users Czech Republic · users Download speed · right logarithmic axis

The pre-2005 World Series uses historical milestone estimates; continuous ITU data begins in 2005.

The speed means the measured download of the fixed connection, not the maximum tariff or the speed of each user. Akamai reported the connection average, Ookla later the test average, and from 2021 the median for the world series. Sections between methodology changes are therefore not connected.

Sources and definitions

The statistics use the indicator "Individuals using the Internet": a person who used the Internet from any place during the last three months. The numbers are calculated from the share of users and population. The last year may be an estimate and values ​​may change when the database is revised.

Permanent exhibition

Exhibits that once looked normal

Windows 95 and a shared computer

The family computer was at the same time a game room, an office, a post office and a gateway to the world. The Internet was used for a while and often according to a pre-written to-do list.

Dial-up internet

Telephone line, busy tone, impulses on the account and speed in kilobits. The connection was an event and the sound of the handshake its unmistakable jingle.

Netscape, Internet Explorer and the Web

Browsers turned the Internet into a graphical medium. Tables, frames, Java applets, ActiveX and pages "optimized" for a single program competed for the standards.

ICQ, IRC and the first online communities

Numeric UINs, "uh-ohs," chat rooms, nicknames, and statuses brought people a sense of constant online presence long before social media.

Email, FTP and files

Electronic mail was the first mass network service. FTP archives, shareware and attachments then showed that the Internet is not just about reading pages.

From personal pages to platforms

Home pages, catalogs and discussion forums have been replaced by search engines, blogs, social networks, video, cloud applications and 24/7 mobile connectivity.

Network gaming lab

Packet War

An original arena game about datagrams that didn't fit in the router. Play alone against bots, or set up an internet room for other players.

  • 1–5autonomous bots
  • 2–8online players
  • 180 sper transmission
Start a Packet War Freeware license

© 2026 Jiří Ludvík. All rights reserved.

01 10 11
UDP ARENA127.0.0.1:2567

Technical cabinet

Modem communication principle

A modem is literally a modulator and demodulator: it converts discrete data into a continuous electrical signal that can pass through the voice channel of the telephone network, while the receiver estimates the original symbols. It does not simply "play zeroes and ones"; it controls the carrier's amplitude, frequency and phase in the presence of noise, echo and distortion.

300-3400 Hz nominal voice band of a classic telephone channel
8 kHz / 8 bits typical PCM digitization G.711: 8000 samples and 64 kbit/s
3429 Bd the highest selectable V.34 symbol rate
33.6 kbit/s maximum full analog duplex V.34 modem

01 / Transmission channel

A telephone line is not an ideal conductor

The subscriber loop is two-wire and was originally optimized for speech. Telephone exchanges therefore suppress very low and high frequencies. In the digital part of the network, speech is typically sampled 8000 times per second; by the Nyquist criterion this creates a theoretical limit of 4 kHz, but practical filters leave a band of roughly 300 to 3400 Hz.

Along the way, the signal suffers from frequency-dependent attenuation, group delay, impulse and thermal noise, crosstalk, PCM quantization distortion, and echo at the transition between two-wire and four-wire circuits. The result is intersymbol interference: the response of one symbol extends into the decision instant of the next.

02 / Modulation

A bit is not the same as a symbol

Bits are grouped into symbols. Each symbol corresponds to a certain carrier state. In binary FSK, one symbol carries one bit; 16-QAM has sixteen states and ideally carries four bits per symbol. Baud is the number of symbols per second, while bit/s measures information rate. Ignoring overhead, Rb = Rs · log2(M).

ASK
information is carried by amplitude; is sensitive to changes in signal level
FSK
symbols select different frequencies; robust but spectrally modest
PSK
carrier phase changes; BPSK has two, QPSK four phase states
QAM
it simultaneously changes the two quadrature components I and Q, i.e. amplitude and phase

s(t) = I(t) cos(2πfct)
− Q(t) sin(2πfct)

Functions I(t) and Q(t) are orthogonal components formed from the symbols and the pulse-shaping waveform. The receiver obtains them by correlating the signal with synchronized cosine and sine waves. It plots the result as a point in the constellation plane and decides which ideal state is nearest.

Interactive oscilloscope

From bits to sound wave and back

The simulation is local and schematic. Noise changes the variance of received points; nothing is sent or connected to the telephone network.

Waveform on the line time →
Constellation after demodulation Q ↑ / I →

03 / Demodulation

The receiver must recover timing, phase and the channel

Demodulation is not simple carrier subtraction. Automatic gain control first stabilizes the level. The carrier and symbol clock recovery loops look for the correct frequency, phase and decision moment. A matched filter maximizes the signal-to-noise ratio and an adaptive equalizer approximately inverts the line's frequency response.

Duplex modems also cancel their own echo: they know the symbols they are transmitting, model their return through the hybrid and subtract it from the received signal. The decision device then selects the nearest constellation point. A trellis decoder can use the Viterbi algorithm to find the most likely sequence of states, while V.42 adds error detection and frame retransmission above the physical layer.

  1. 1A/D + AGCsampling and level
  2. 2Synchronizationcarrier and symbol timing
  3. 3Matched filternoise suppression
  4. 4Equalizerchannel correction
  5. 5DemapperI/Q → symbols
  6. 6Decodersymbols → bits

04 / Physical limit

More states alone will not save speed

The denser the constellation, the smaller the distance between neighboring states and the easier it is for noise to confuse them. Shannon capacity of an ideal channel C = B · log2(1 + S/N) says that the achievable data rate is limited jointly by bandwidth B and the linear signal-to-noise ratio S/N. The decibel conversion is S/N = 10SNRdB/10.

05 / Assembling the connection

A modem and a fax machine sound similar but use a different protocol

06 / Fax transmission

Where the handshake frequency is really different

A calling automatic fax sends CNG at 1100 Hz: 0.5 seconds of tone followed by 3 seconds of silence, both with ±15% tolerance. This announces: "I am not a person; I want to send a fax." By contrast, a regular data modem using V.8 waits for the answering ANSam at 2100 Hz and then sends a digitally coded capabilities menu.

One important qualification: the answering fax sends CED at 2100 Hz as well (±15 Hz, 2.6 to 4.0 s continuously). Modem ANSam has a tighter tolerance of ±1 Hz, amplitude modulation of 15 Hz, and typically reverses phase every 450 ms. So the devices don't differentiate the service just by a single frequency, but by direction, cadence, modulation and following protocol.

After the tones, the fax enters the T.30 control phase: HDLC frames run at 300 bit/s over FSK V.21 channel 2. Frequency 1850 Hz means binary 0 and 1650 Hz binary 1. Receiver sends DIS with capabilities, transmitter replies DCS with selected mode, followed by training, TCF and CFR confirmation. Only then is the page transmitted using the faster V.27 ter, V.29 or V.17 modulation; V.17 uses 2400 Bd QAM, adaptive equalization and trellis coding up to 14.4 kbit/s.

Brief listening for signals

The volume is intentionally low. The sound will start only when pressed.

Ready to listen.

Complete connection setup

Synthetic museum reconstructions according to ITU-T V.8, V.34, V.21, T.30 and V.17. They preserve the character and sequence of phases, they are not a bit-accurate recording of a specific device.

DATA / V.34The modem establishes a data connection

Ready: dialing a number and setting up a call by phone.

  1. DTMF number dialing
  2. Return ringtone
  3. ANSam · 2100 Hz, AM 15 Hz
  4. V.8 · CM, JM and CJ via V.21
  5. V.34 phase 2 · probing and ranging
  6. Phase 3 · equalizer and echo cancellation
  7. Phase 4 · final training and parameters
  8. Data mode
FAX / T.30 + V.17The fax establishes a document transmission

Ready: number dialling and the fax calling tone.

  1. DTMF number dialing
  2. Ringtone and CNG · 1100 Hz
  3. CED · response tone 2100 Hz
  4. DIS · receiver capabilities via V.21
  5. DCS · selected transmission mode
  6. Training and TCF · channel control
  7. CFR · receiver is ready
  8. V.17 · start of image data

Normative sources

Numerical parameters are based on ITU-T recommendations:

  • V.8 – starting data sessions, ANSam and CM/JM exchange,
  • V.34 – duplex modems up to 33.6 kbit/s, symbol rates and training,
  • V.21 – 300bit/s FSK and pair of frequencies,
  • T.30 – fax CNG/CED, call phases and control procedures,
  • V.17 – high-speed fax modulation up to 14.4 kbit/s.

Security wing

When the trusting network started to fight back

The Internet was not designed to be a public square for billions of people. With its growth, therefore, new attacks and defense layers were created. This exhibit traces one important branch of the broader history of the Internet.

The web takes up residence at home

Static pages, FTP passwords, shared accounts and minimal automatic updates.

Macro viruses and email attachments

An attachment from a known person didn't seem suspicious yet. That quickly changed.

Worms and unprotected ports

Blaster, Slammer and similar incidents have shown how quickly the Internet contagion spreads.

Phishing is coming of age

Attacks are no longer just technical. They started copying banks, services and work communication.

HTTPS everywhere

Certificates became cheaper, automated, and encryption became the expected standard.

Zero trust and defense in depth

Strong identity, multi-factor, isolation, monitoring, CSP, HSTS, DNSSEC and secure development.

Security Wing Laboratory

Interactive demonstrations without a real attack

Password strength

Try typing the password. The sample only calculates orientation resistance according to the length and variety of characters, it does not send anything anywhere.

Enter the password and the museum will estimate its condition.

Suspicious link detector

Enter a URL and see which signals a person should check before clicking.

    Security header puzzle

    Choose a script and see which headers give the browser modern controls.

    
        
    
      
    
    
    

    
    
      
    
        
    Internet today
    
        
    A network that is almost everywhere
    
        
    Today's Internet is a mixture of optical paths, mobile networks, data centers, open protocols and security mechanisms. The user does not see most of this infrastructure, yet uses it almost constantly.
    
      
    
      
    
        
    
          
    Optics and broadband connections
    
          
    Today, home lines carry more data per second than entire academic backbones of the past. The bottleneck is usually no longer the telephone voice channel.
    
        
    
        
    
          
    Mobile internet
    
          
    Data networks moved the Internet from the desk to the pocket. Connection is no longer a special mode of the computer, but a permanent state of the phone.
    
        
    
        
    
          
    Cloud and CDN
    
          
    The service does not have to live on one server or in one country. Compute, storage and copies of content are spread across data centers close to users.
    
        
    
        
    
          
    DNS, DNSSEC and HTTPS
    
          
    The name system translates names into addresses, DNSSEC allows you to verify the response, and HTTPS protects the traffic between the client and the service.
    
        
    
        
    
          
    Streaming and communication
    
          
    Video, voice, gaming and live streaming require low latency, buffers and protocols that can adapt to the quality of the connection.
    
        
    
        
    
          
    IPv6 and further growth
    
          
    The new address space responds to billions of connected devices. In addition to computers and phones, there are online sensors, cars, televisions and industrial systems.