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Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book". By the time the standard was released, newer networking systems with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance.
In digital radio, packet radio is the application of packet switching techniques to digital radio communications. Packet radio uses a packet switching protocol as opposed to circuit switching or message switching protocols to transmit digital data via a radio communication link.
In telecommunications, an acoustic coupler is an interface device for coupling electrical signals by acoustical means—usually into and out of a telephone.
Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK, in which the carrier is shifted between two discrete frequencies to transmit binary information.
The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls.
The Hayes command set is a specific command language originally developed by Dale Heatherington and Dennis Hayes for the Hayes Smartmodem in 1981.
U.S. Robotics Corporation, often called USR, is a company that produces USRobotics computer modems and related products. Its initial marketing was aimed at bulletin board systems, where its high-speed HST protocol made FidoNet transfers much faster, and thus less costly. During the 1990s it became a major consumer brand with its Sportster line. The company had a reputation for high quality and support for the latest communications standards as they emerged, notably in its V.Everything line, released in 1996.
Internet access is a facility or service that provides connectivity for a computer, a computer network, or other network device to the Internet, and for individuals or organizations to access or use applications such as email and the World Wide Web. Internet access is offered for sale by an international hierarchy of Internet service providers (ISPs) using various networking technologies. At the retail level, many organizations, including municipal entities, also provide cost-free access to the general public. Types of connections range from fixed-line cable to mobile and satellite.
Hayes Microcomputer Products was a US-based manufacturer of modems. The company is known for the Smartmodem, which introduced a control language for operating the functions of the modem via the serial interface, in contrast to manual operation with front-panel switches. This smart modem approach dramatically simplified and automated operation. Today almost all modems use a variant of the Hayes AT command set.
The V.23 standard was an early modem standard first approved by ITU-T precursor CCITT in 1964.
The Bell 202 modem was an early (1976) modem standard developed by the Bell System. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second (bit/s), half-duplex. It has separate sets of circuits for 1200 bit/s and 300 bit/s rates. These signalling protocols, also used in third-party modems, are referred to generically as Bell 202 modulation, and any device employing it as Bell-202-compatible.
In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in bits per second.
A digital subscriber line (DSL) modem is a device used to connect a computer or router to a telephone line which provides the digital subscriber line (DSL) service for connection to the Internet, which is often called DSL broadband. The modem connects to a single computer or router, through an Ethernet port, USB port, or is installed in a computer PCI slot.
Novation, Inc., is an early modem manufacturer whose CAT series were popular in the early home computer market in the late 1970s and early 1980s, notably on the Apple II. The Hayes Smartmodem 300, introduced in 1981, helped kill off Novation and many other early modem companies over the next few years.
Microcom, Inc., was a major modem vendor during the 1980s, although never as popular as the "big three", Hayes, U.S. Robotics (USR) and Telebit. Nevertheless, Microcom holds an important place in modem history for introducing the MNP error-correction and compression protocols, which were widely used under license by most modem manufacturers in the 1990s. The company went public in 1987. Compaq purchased publicly outstanding shares of the company in 1997.
A modulator-demodulator, commonly referred to as a modem, is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carrier wave signals to encode digital information, while the receiver demodulates the signal to recreate the original digital information. The goal is to produce a signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from LEDs to radio.
Singapore Teleview or known as Camp-Camp View or Ke Pik was a Singaporean videotext service. In the mid 1980s, the Telecom Authority of Singapore entered into a joint venture development with GEC Marconi in the UK to develop a photo-videotext public service. Selected engineers were sent to the UK to work within the Marconi development team stationed at Fleet, Hampshire, England. Singapore was the first country in the world to launch an interactive information service to the public which included photographic images. The service started trials during late 1987 using specifically designed terminals. Controlled trials had been conducted since 1987 as the infrastructure was installed and trialed successfully. It finally went into full public service in 1991.
Popcom was a line of modems marketed by the Prentice Corporation of Sunnyvale, California, introduced in 1984. The line comprised six models—X100, X150, C100, C150, C200, C250—the C models being internal modems meant to plug into a free ISA expansion slot of a PC compatible, while the X models were compact external units intended to be plugged into a wall indefinitely and connected to the computer via a serial cable. The X100 and X150 were noted by the press for their very small physical footprint among its contemporaries in the market.
References
- ↑ "BSP 592-039-100: Data Set 212AR-L1A/2A -- Transmitter-Receiver -- Description and Operation", Bell System Practices, American Telephone & Telegraph Co, June 1979
- 1 2 Frank J. Derfler, "The Universal Data Systems' 212 LP modem", InfoWorld, pp. 52-53, 9 August 1982.
- ↑ Frank J. Derfler Jr., "Selecting the right modem", PC Magazine, pp. 224-233, January 1983.
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