Overview
This lecture covers the evolution of early computer networking, focusing on dial-up connections, the use of telephone networks for data transfer, and the development of Usenet.
Early Computer Networking
- Early computer networks connected devices within close physical proximity using primitive technologies.
- There was a growing need to connect computers over longer distances to share data.
Telephone Networks as Data Infrastructure
- The public switched telephone network (PSTN), also called plain old telephone service (POTS), existed globally by the late 1970s.
- Graduate students at Duke University realized PSTN could be repurposed for computer data transfer.
Birth of Usenet and Dial-up
- Usenet was created as a way for colleges to exchange messages using dial-up connections.
- Dial-up connections use telephone lines to transfer data by dialing a phone number.
- This system was an important precursor to later internet connectivity methods.
Modems and Data Transmission
- Data is transferred across dial-up connections via devices called modems (modulator/demodulator).
- Modems convert computer data into audible signals for transmission over telephone lines.
- This process is similar to line coding in Ethernet, which encodes data for transmission across cables.
Evolution of Baud Rates
- Baud rate measures how many bits per second can be sent over a phone line.
- In the late 1950s, transfer speeds were about 110 bits per second.
- Usenet's era saw baud rates around 300 bits per second.
- By the early 1990s, dial-up reached speeds of 14.4 kilobits per second.
Modern Relevance
- Dial-up has been largely replaced by broadband, but it remains in use in some rural areas.
- For decades, dial-up was the primary way for computers to communicate over long distances.
Key Terms & Definitions
- PSTN (Public Switched Telephone Network) — the global telephone network used for voice and, later, data transfer.
- POTS (Plain Old Telephone Service) — another name for the traditional telephone system.
- Dial-up connection — a data connection established by dialing a phone number to transfer data over telephone lines.
- Modem (modulator/demodulator) — a device that converts digital data to audible signals and vice versa.
- Baud rate — the number of bits transmitted per second over a communication channel.
- Usenet — an early system for exchanging messages using dial-up connections between institutions.
Action Items / Next Steps
- Review how dial-up connections work and their historical significance.
- Understand the differences between dial-up and modern broadband technologies.