The telephone network was the first global electrical network built for ordinary people. Long before the internet existed, it already had the main parts of a modern communications system: an addressing scheme (phone numbers), switching (routing a call to the right line), signalling (telling the network what you want), and a hierarchy of local and long-distance links. The early internet ran on top of it, and dial-up modems turned voice lines into data links.
The core idea¶
A telephone turns sound into a varying electrical current and back again. Speaking into the transmitter vibrates a diaphragm, which changes the current flowing in the line. At the other end, that changing current moves another diaphragm and recreates the sound. The signal is an analog of the sound wave. That is where the word "analog" comes from.
Everything else in telephone history was built around making that basic circuit:
- Connect to anyone: switchboards, then automatic switches.
- Reach farther: amplifiers, loading coils, undersea cables.
- Carry more calls: multiplexing and digitization.
- Cost less: automation, competition, and eventually packet-switched VoIP.
How a classic landline works¶
A traditional copper landline, often called POTS ("plain old telephone service"), is a pair of copper wires running from the home to a central office (CO).
- The CO supplies about 48 V DC. Because the power comes from the CO, a copper phone keeps working during a home power outage.
- Lifting the handset closes the circuit (off-hook). Current flows, and the switch responds with dial tone.
- The phone dials either by interrupting that current in pulses (rotary) or by sending pairs of audio tones (Touch-Tone).
- To ring the phone, the CO sends a higher-voltage AC signal of about 90 V at 20 Hz, which drives the bell.
Topics¶
- The invention of the telephone (1876): Bell, Gray, Meucci, and the first calls in Ontario.
- Building the early network: carbon transmitters, switchboards, operators, and the founding of Bell Canada.
- Automatic switching and the rotary dial: Strowger, pulse dialing, and the classic Model 500.
- Going long distance: amplifiers, area codes, direct dialing, and undersea cables.
- The digital network: PCM and T1, Touch-Tone, electronic switches, phreaking, SS7, and deregulation.
- Dial-up modems: how data travelled over voice lines, and why it stopped at 56k.
- VoIP and the retirement of copper: how the analog phone network is being replaced.
Related: Using a rotary phone today and VoIP.
Timeline at a glance¶
| Year | Milestone |
|---|---|
| 1844 | Morse's telegraph line shows electricity can carry messages |
| 1876 | Bell's telephone patent; first long-distance call (Brantford to Paris, Ontario) |
| 1878 | First commercial telephone exchange (New Haven, Connecticut) |
| 1880 | Bell Telephone Company of Canada incorporated |
| 1891 | Strowger patents the automatic exchange |
| 1915 | First transcontinental call across the U.S. |
| 1947 | Transistor invented at Bell Labs; North American Numbering Plan creates area codes |
| 1949 | Western Electric Model 500 desk phone |
| 1951 | First direct-dialed long-distance call |
| 1956 | TAT-1, the first transatlantic telephone cable |
| 1962 | T1 digital carrier; Bell 103 modem |
| 1963 | Touch-Tone (DTMF) dialing introduced |
| 1965 | 1ESS, the first stored-program electronic switch |
| 1979 | Nortel DMS-100 digital switch |
| 1984 | AT&T breakup |
| 1998 | V.90 56k modem standard |
| 2002 | SIP standardized (RFC 3261) |
| 2020s | Carriers retire copper and move home phone service to fibre and VoIP |