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V.42
The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. ''Note:'' the '' bis'' and ''ter'' suffixes are ITU-T standard designators of successive iterations of a standard (''bis'' and ''ter'' are derived from the Latin for "twice" and "thrice"). General standards ''Applies to V.1–V.9'' *V.1 is an ITU-T recommendation, entitled ''Equivalence between binary notation symbols and the significant conditions of a two-condition code.'' *V.2 is an ITU-T recommendation, approved in November 1988, titled ''Power levels for data transmission over telephone lines.'' *V.4 is an ITU-T recommendation, approved in November 1988, titled ''General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks.'' *V.5 was an ITU-T recommendation, approved in November 1988, titled ''Standardization of data signall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hayes Microcomputer Products
Hayes Microcomputer Products was a U.S.-based manufacturer of modems. The company is well 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 command set. Hayes was a major brand in the modem market from the introduction of the original 300 bit/s Smartmodem in 1981. They remained a major vendor throughout the 1980s, periodically introducing models with higher throughput. Their competition through this period was primarily from two other high-end vendors, US Robotics and Telebit, while other companies mostly sold into niches or were strictly low-end offerings. In the early 1990s a number of greatly cost-reduced high-performance modems were released by competitors, notably the SupraFAXModem 14400, which eroded price point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or 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 Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AT&T Paradyne
Paradyne, also referred to as AT&T Paradyne, was a maker of computer networking and telecommunications hardware, based in Largo, Florida. The company formed in 1969 to supply computer communications systems and expanded steadily through the 1970s and 80s. During these period they operated in the high-end modem market and competed with Motorola Codex, Racal-Milgo, and divisions of AT&T and IBM. As one of its first major purchases after the 1982 Breakup of the Bell System, AT&T purchased the company for $250 million in 1989. The company grew to become a major supplier in the digital subscriber line (DSL) industry as that expanded. When AT&T spun off Lucent in 1996, Paradyne moved to the new company. Lucent quickly sold Paradyne to Texas Pacific Group (TPG Capital) for $175 million where it became Paradyne Networks. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First-mover Advantage
In marketing strategy, first-mover advantage (FMA) is the competitive advantage gained by the initial ("first-moving") significant occupant of a market segment. First-mover advantage enables a company or firm to establish strong brand recognition, customer loyalty, and early purchase of resources before other competitors enter the market segment. First movers in a specific industry are almost always followed by competitors that attempt to capitalise on the first movers' success. These followers are also aiming to gain market share; however, most of the time the first-movers will already have an established market share, with a loyal customer base that allows them to maintain their market share. Mechanisms leading to first-mover advantages The three primary sources of a first-mover advantage are technology leadership, control of resources, and buyer switching costs. Technology leadership First movers can make their technology/product/services harder for later entrants to replicat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shaping Codes
In digital communications shaping codes are a method of encoding that changes the distribution of signals to improve efficiency. Description Typical digital communication systems uses M-Quadrature Amplitude Modulation(QAM) to communicate through an analog channel (specifically a communication channel with Gaussian noise). For Higher bit rates(M) the minimum signal-to-noise ratio (SNR) required by a QAM system with Error Correcting Codes is about 1.53 dB higher than minimum SNR required by a Gaussian source(>30% more transmitter power) as given in Shannon–Hartley theorem : C = B \log_2 \left( 1+\frac \right) where :''C'' is the channel capacity in bits per second; :''B'' is the bandwidth of the channel in hertz; : ''S'' is the total signal power over the bandwidth and : ''N'' is the total noise power over the bandwidth. :''S/N'' is the signal-to-noise ratio of the communication signal to the Gaussian noise interference expressed as a straight power ratio (not as decibe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symbol Rate
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''. Symbols A symbol may be described as either a pulse in digital baseband transmission or a tone in passband transmission using modems. A symbol is a waveform, a state or a significant condition of the communication channel that ''persists'', for a fixed period of time. A sending device places symbols on the channel at a fixed and known symbol rate, and the receiving device has the job of detecting the sequence of symbols in order to reconstruct the transmitted data. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Full-duplex
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half-duplex
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a computer terminal, and a ''DCE'' (''data circuit-terminating equipment'' or ''data communication equipment''), such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is ''TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange'', issued in 1997. The RS-232 standard had been commonly used in computer serial ports and is still widely used in industrial communication devices. A serial port complying with the RS-232 standard was once a standard feature of many types of computers. Personal computers used them for connection ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency-shift Keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. 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 (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the 1 is called the mark frequency and the 0 is called the space frequency. Modulating and demodulating Reference implementations of FSK modems exist and are documented in detail. The demodulation of a binary FSK signal can be done using the Goertzel algorithm very efficiently, even on low-power microcontrollers. Variations Multiple frequency-shift keying Continuous-phase frequency-shift keying In principle FSK can be implemented by using completely independent free-running oscillat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Duplex (telecommunications)
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quadrature Amplitude Modulation
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signals, or two digital bit streams, by changing (''modulating'') the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves are of the same frequency and are out of phase with each other by 90°, a condition known as orthogonality or quadrature. The transmitted signal is created by adding the two carrier waves together. At the receiver, the two waves can be coherently separated (demodulated) because of their orthogonality property. Another key property is that the modulations are low-frequency/low-bandwidth waveforms compared to the carrier frequency, which is known as the narrowband assumption. Phase modulation (analog PM) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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