Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. In Computer hardware, a peripheral device is any device attached to a computer in order to expand its functionality (basically input and output devices together are known In Telecommunications, modulation is the process of varying a periodic Waveform, i In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Demodulation is the act of removing the Modulation from an analog signal to get the original Baseband signal back The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's Modems can be used over any means of transmitting analog signals, from driven diodes to radio. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light.

The most familiar example is a voiceband modem that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Serial, or Network connection. The binary numeral system, or base-2 number system, is a Numeral system that represents numeric values using two symbols usually 0 and 1. A telephone line or telephone circuit (or just line or circuit within the Industry) is a single-user circuit on a Telephone Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second, or "bps". In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b They can also be classified by Baud, the number of times the modem changes its signal state per second. In Telecommunications and Electronics, baud (ˈbɔːd unit symbol "Bd" is synonymous to symbols/s or pulses/s.

Baud is NOT the modem's speed. The baud rate varies, depending on the modulation technique used. Original Bell 103 modems used a modulation technique that saw a change in state 300 times per second. They transmitted 1 bit for every baud, and so a 300 bit/s modem was also a 300-baud modem. However, casual computerists confused the two. A 300 bit/s modem is the only modem whose bit rate matches the baud rate. A 2400 bit/s modem changes state 600 times per second, but due to the fact that it transmits 4 bits for each baud, 2400 bits are transmitted by 600 baud, or changes in states.

Faster modems are used by Internet users every day, notably cable modems and ADSL modems. A cable modem is a type of Modem that provides access to a data signal sent over the Cable television infrastructure ADSL modem or DSL modem is a device used to connect a single Computer or Router to a DSL phone line in order to use an ADSL In telecommunications, "radio modems" transmit repeating frames of data at very high data rates over microwave radio links. In Telecommunication and Computer science, serial communication is the process of sending data one Bit at one time sequentially over a Communication Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Some microwave modems transmit more than a hundred million bits per second. Optical modems transmit data over optical fibers. In Fiber-optic communications wavelength-division multiplexing ( WDM) is a technology which multiplexes multiple optical carrier signals on a An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length Most intercontinental data links now use optical modems transmitting over undersea optical fibers. A submarine communications cable is a cable laid beneath the sea to carry Telecommunications between countries Optical modems routinely have data rates in excess of a billion (1x10⁹) bits per second. One kilobit per second (kbit/s or kb/s or kbps) as used in this article means 1000 bits per second and not 1024 bits per second. In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission For example, a 56k modem can transfer data at up to 56,000 bits per second over the phone line.

History

News wire services in the 1920s used multiplex equipment that met the definition, but the modem function was incidental to the multiplexing function, so they are not commonly included in the history of modems. News agency (alternative A news agency is an organization of Journalists established to supply News reports to organizations in the News trade For multiplexing in electronics and signal processing see Multiplexer. George Stibitz connected a New Hampshire teletype to a computer in New York City by phone lines in 1940. George Robert Stibitz ( April 20, 1904 &ndash January 31, 1995) is internationally recognized as a father of the modern digital computer A teleprinter ( Modems in the United States were part of the SAGE air-defense system in the 1950s, connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the U. The Semi-Automatic Ground Environment ( SAGE) was an automated control system for tracking and intercepting enemy Bomber aircraft used by NORAD from S. and Canada. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page SAGE ran on dedicated communications lines, but the devices at each end were otherwise similar in concept to today's modems.

A few years later, a chance meeting between the CEO of American Airlines and a regional manager of IBM led to development of a "mini-SAGE" as an automated airline ticketing system. A chief executive officer ( CEO) or chief executive is typically the highest-ranking corporate officer ( executive) or administrator American Airlines Inc (AA is a US -based airline and the world's Largest airline in total passenger miles transported and passenger fleet size The terminals were at ticketing offices, tied to a central computer that managed availability and scheduling. The system, known as SABRE, is the ancestor of today's Sabre system. Sabre is a Computer reservations system /global distribution system (GDS used by Airlines Railways Hotels Travel agents and other

AT&T monopoly in the United States

For many years, AT&T maintained a monopoly in the United States on the use of its phone lines, allowing only AT&T-supplied devices to be attached to its network. Before proposing a merge request please see Talk and see if the merger you propose has recently been made and For the growing group of computer users, AT&T introduced two digital sub-sets in 1958. One is the wideband device shown in the picture to the right. The other was a low-speed modem, which ran at 200 baud. In Telecommunications and Electronics, baud (ˈbɔːd unit symbol "Bd" is synonymous to symbols/s or pulses/s.

Legacy modem for leased line operation.

In the summer of 1960, the name Data-Phone was introduced to replace the earlier term digital subset. The 202 Data-Phone was a half-duplex asynchronous service that was marketed extensively in late 1960. A duplex Communication system is a system composed of two connected parties or devices which can communicate with one another in both directions In 1962, the 201A and 201B Data-Phones were introduced. They were synchronous modems using two-bit-per-baud phase-shift keying (PSK). Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal The 201A operated half-duplex at 2000 bit/s over normal phone lines, while the 201B provided full duplex 2400 bit/s service on four-wire leased lines, the send and receive channels running on their own set of two wires each. A duplex Communication system is a system composed of two connected parties or devices which can communicate with one another in both directions

The famous 103A was also introduced in 1962. It provided full-duplex service at up to 300 baud over normal phone lines. Frequency-shift keying (FSK) was used with the call originator transmitting at 1070 or 1270 Hz and the answering modem transmitting at 2025 or 2225 Hz. Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the KSR33, the ASR33, and the IBM 2741. Introduced about 1963, Teletype Corporation 's ASR33 was a very popular model of Teleprinter. The 2741 was a low-speed Dumb terminal introduced in 1965. It combined a ruggedized Selectric Typewriter AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems.

The Carterfone decision

The Novation CAT acoustically coupled modem

Before 1968, AT&T maintained a monopoly on what devices could be electrically connected to its phone lines. This led to a market for 103A-compatible modems that were mechanically connected to the phone, through the handset, known as acoustically coupled modems. In Telecommunications the term acoustic coupler has the following meanings An interface device for coupling electrical signals by Particularly common models from the 1970s were the Novation CAT (shown in the image) and the Anderson-Jacobson, spun off from an in-house project at the Lawrence Livermore National Laboratory. Novation was 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 The Lawrence Livermore National Laboratory ( LLNL) in Livermore California is a scientific research laboratory founded by the University of California in 1952

Hush-a-Phone v. FCC was a seminal ruling in United States telecommunications law decided by the DC Circuit Court of Appeals on November 8, 1956. Hush-a-Phone v United States, 238 F2d 266 (DC Cir 1956 was a seminal ruling in United States Telecommunications law decided by the DC Circuit The United States of America —commonly referred to as the The United States Court of Appeals for the District of Columbia Circuit, known informally as the D Events 1519 - Hernán Cortés enters Tenochtitlán and Aztec ruler Moctezuma welcomes him with great a Celebration Year 1956 ( MCMLVI) was a Leap year starting on Sunday (link will display full calendar of the Gregorian calendar. The District Court found that it was within the FCC's authority to regulate the terms of use of AT&T's equipment. Subsequently, the FCC examiner found that as long as the device was physically attached it would not threaten to degenerate the system. Later, in the Carterfone decision, the FCC passed a rule setting stringent AT&T-designed tests for electronically coupling a device to the phone lines. The Carterfone is a device invented by Thomas Carter. It connects a two-way mobile radio system to the Public Switched Telephone Network (PSTN AT&T made these tests complex and expensive, so acoustically coupled modems remained common into the early 1980s.

In December 1972, Vadic introduced the VA3400. This device was remarkable because it provided full duplex operation at 1200 bit/s over the dial network, using methods similar to those of the 103A in that it used different frequency bands for transmit and receive. In November 1976, AT&T introduced the 212A modem to compete with Vadic. It was similar in design to Vadic's model, but used the lower frequency set for transmission. It was also possible to use the 212A with a 103A modem at 300 bit/s. According to Vadic, the change in frequency assignments made the 212 intentionally incompatible with acoustic coupling, thereby locking out many potential modem manufacturers. In 1977, Vadic responded with the VA3467 triple modem, an answer-only modem sold to computer center operators that supported Vadic's 1200-bit/s mode, AT&T's 212A mode, and 103A operation.

The Smartmodem and the rise of BBSes

US Robotics Sportster 14,400 Fax modem (1994)

The next major advance in modems was the Smartmodem, introduced in 1981 by Hayes Communications. US Robotics (often referred to by its abbreviation USR and not to be confused with U Hayes Microcomputer Products was a US -based manufacturer of Modems They are particularly well known for their Smartmodem, which introduced the ability The Smartmodem was an otherwise standard 103A 300-bit/s modem, but was attached to a small controller that let the computer send commands to it and enable it to operate the phone line. The command set included instructions for picking up and hanging up the phone, dialing numbers, and answering calls. The basic Hayes command set remains the basis for computer control of most modern modems. The Hayes command set is a specific command-language originally developed for the Hayes Smartmodem 300 Baud modem

Prior to the Hayes Smartmodem, modems almost universally required a two-step process to activate a connection: first, the user had to manually dial the remote number on a standard phone handset, and then secondly, plug the handset into an acoustic coupler. Hardware add-ons, known simply as dialers, were used in special circumstances, and generally operated by emulating someone dialing a handset.

With the Smartmodem, the computer could dial the phone directly by sending the modem a command, thus eliminating the need for an associated phone for dialing and the need for an acoustic coupler. The Smartmodem instead plugged directly into the phone line. This greatly simplified setup and operation. Terminal programs that maintained lists of phone numbers and sent the dialing commands became common.

The Smartmodem and its clones also aided the spread of bulletin-board systems (BBSs). A Bulletin Board System, or BBS, is a Computer system running software that allows users to connect and login to Modems had previously been typically either the call-only, acoustically coupled models used on the client side, or the much more expensive, answer-only models used on the server side. The Smartmodem could operate in either mode depending on the commands sent from the computer. There was now a low-cost server-side modem on the market, and the BBSs flourished.

Softmodem (dumb modem)

Main article: Softmodem

A PCI Winmodem/Softmodem (on the left) next to a traditional ISA modem (on the right). A Softmodem, or software modem is a Modem with minimal hardware capacities designed to use a host computer's resources (mostly CPU power and RAM but sometimes Notice the less complex circuitry of the modem on the left.

A Winmodem or Softmodem is a stripped-down modem that replaces tasks traditionally handled in hardware with software. Hardware is a general term that refers to the physical artifacts of a Technology. In this case the modem is a simple digital signal processor designed to create sounds, or voltage variations, on the telephone line. Softmodems are cheaper than traditional modems, since they have fewer hardware components. One downside is that the software generating the modem tones is not simple, and the performance of the computer as a whole often suffers when it is being used. For online gaming this can be a real concern. Another problem is lack of portability such that other OSes (such as Linux) may not have an equivalent driver to operate the modem. Linux (commonly pronounced ˈlɪnəks A Winmodem might not work with a later version of Microsoft Windows, if its driver turns out to be incompatible with that later version of the operating system.

Apple's GeoPort modems from the second half of the 1990s were similar. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics GeoPort was a serial data system used on some models of the Apple Macintosh. Although a clever idea in theory, enabling the creation of more-powerful telephony applications, in practice the only programs created were simple answering-machine and fax software, hardly more advanced than their physical-world counterparts, and certainly more error-prone and cumbersome. The software was finicky and ate up significant processor time, and no longer functions in current operating system versions.

Almost all modern modems also do double-duty as a fax machine as well. Fax (short for facsimile, from Latin fac simile, "make similar" i Digital faxes, introduced in the 1980s, are simply a particular image format sent over a high-speed (9600/1200 bit/s) modem. This is a comparison of Image file formats. General Ownership of the format and related information Software running on the host computer can convert any image into fax-format, which can then be sent using the modem. Such software was at one time an add-on, but since has become largely universal.

Narrowband/phone-line dialup modems

28. 8 kbit/s serial-port modem from Motorola

A standard modem of today contains two functional parts: an analog section for generating the signals and operating the phone, and a digital section for setup and control. In Computing, a serial port is a Serial communication physical interface through which information transfers in or out one Bit at a time (contrast Motorola Inc ( is an American, multinational Fortune 100, Telecommunications company based in Schaumburg Illinois. This functionality is actually incorporated into a single chip, but the division remains in theory. In operation the modem can be in one of two "modes", data mode in which data is sent to and from the computer over the phone lines, and command mode in which the modem listens to the data from the computer for commands, and carries them out. A typical session consists of powering up the modem (often inside the computer itself) which automatically assumes command mode, then sending it the command for dialing a number. After the connection is established to the remote modem, the modem automatically goes into data mode, and the user can send and receive data. When the user is finished, the escape sequence, "+++" followed by a pause of about a second, is sent to the modem to return it to command mode, and the command ATH to hang up the phone is sent. This article refers to codes used as commands for computing devices

The commands themselves are typically from the Hayes command set, although that term is somewhat misleading. The Hayes command set is a specific command-language originally developed for the Hayes Smartmodem 300 Baud modem The original Hayes commands were useful for 300 bit/s operation only, and then extended for their 1200 bit/s modems. Faster speeds required new commands, leading to a proliferation of command sets in the early 1990s. Things became considerably more standardized in the second half of the 1990s, when most modems were built from one of a very small number of "chip sets". We call this the Hayes command set even today, although it has three or four times the numbers of commands as the actual standard.

Increasing speeds (V. 21 V. 22 V. 22bis)

A 2400 bit/s modem for a laptop.

The 300 bit/s modems used frequency-shift keying to send data. Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave In this system the stream of 1s and 0s in computer data is translated into sounds which can be easily sent on the phone lines. In the Bell 103 system the originating modem sends 0s by playing a 1070 Hz tone, and 1s at 1270 Hz, with the answering modem putting its 0s on 2025 Hz and 1s on 2225 Hz. These frequencies were chosen carefully, they are in the range that suffer minimum distortion on the phone system, and also are not harmonics of each other. In Acoustics and Telecommunication, the harmonic of a Wave is a component Frequency of the signal that is an Integer

In the 1200 bit/s and faster systems, phase-shift keying was used. Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal In this system the two tones for any one side of the connection are sent at the similar frequencies as in the 300 bit/s systems, but slightly out of phase. By comparing the phase of the two signals, 1s and 0s could be pulled back out, for instance if the signals were 90 degrees out of phase, this represented two digits, "1,0", at 180 degrees it was "1,1". In this way each cycle of the signal represents two digits instead of one. 1200 bit/s modems were, in effect, 600 symbols per second modems (600 baud modems) with 2 bits per symbol.

Voiceband modems generally remained at 300 and 1200 bit/s (V.21 and V.22) into the mid 1980s. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network A V.22bis 2400-bit/s system similar in concept to the 1200-bit/s Bell 212 signalling was introduced in the U. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network S. , and a slightly different one in Europe. By the late 1980s, most modems could support all of these standards and 2400-bit/s operation was becoming common.

For more information on baud rates versus bitrates, see the companion article List of device bandwidths. This is a list of device bandwidths: the Net bit rate (or more informally Digital bandwidth) of some computer devices employing methods of data transport is quantified

Increasing speeds (one-way proprietary standards)

Many other standards were also introduced for special purposes, commonly using a high-speed channel for receiving, and a lower-speed channel for sending. One typical example was used in the French Minitel system, in which the user's terminals spent the majority of their time receiving information. The Minitel is a Videotex Online service accessible through the Telephone lines and is considered one of the world's most successful pre- World The modem in the Minitel terminal thus operated at 1200 bit/s for reception, and 75 bit/s for sending commands back to the servers. A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine

Three U. S. companies became famous for high-speed versions of the same concept. Telebit introduced its Trailblazer modem in 1984, which used a large number of 36 bit/s channels to send data one-way at rates up to 18,400 bit/s. Telebit was a US -based Modem manufacturer most notable for their TrailBlazer series of high-speed modems A single additional channel in the reverse direction allowed the two modems to communicate how much data was waiting at either end of the link, and the modems could change direction on the fly. Colloquial usage In colloquial use on the fly means something created when needed The Trailblazer modems also supported a feature that allowed them to "spoof" the UUCP "g" protocol, commonly used on Unix systems to send e-mail, and thereby speed UUCP up by a tremendous amount. UUCP is an Abbreviation for Unix to Unix CoPy. The term generally refers to a suite of Computer programs and protocols allowing remote execution Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a Store-and-forward method of writing sending receiving Trailblazers thus became extremely common on Unix systems, and maintained their dominance in this market well into the 1990s.

U.S. Robotics (USR) introduced a similar system, known as HST, although this supplied only 9600 bit/s (in early versions at least) and provided for a larger backchannel. US Robotics (often referred to by its abbreviation USR and not to be confused with U Rather than offer spoofing, USR instead created a large market among Fidonet users by offering its modems to BBS sysops at a much lower price, resulting in sales to end users who wanted faster file transfers. Sysop (ˈsɪsɒp is short for " System operator " It is a commonly used term for an administrator of a multi-user website such as a Bulletin board system Hayes was forced to compete, and introduced its own 9600-bit/s standard, Express 96 (also known as "Ping-Pong"), which was generally similar to Telebit's PEP. Hayes, however, offered neither protocol spoofing nor sysop discounts, and its high-speed modems remained rare.

4800 and 9600 (V. 27ter, V. 32)

Echo cancellation was the next major advance in modem design. The term Echo cancellation is used in Telephony to describe the process of removing echo from a voice communication in order to improve voice quality on Local telephone lines use the same wires to send and receive, which results in a small amount of the outgoing signal bouncing back. This signal can confuse the modem. Is the signal it is "hearing" a data transmission from the remote modem, or its own transmission bouncing back? This was why earlier modems split the signal frequencies into answer and originate; each modem simply didn't listen to its own transmitting frequencies. Even with improvements to the phone system allowing higher speeds, this splitting of available phone signal bandwidth still imposed a half-speed limit on modems. Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum

Echo cancellation got around this problem. Measuring the echo delays and magnitudes allowed the modem to tell if the received signal was from itself or the remote modem, and create an equal and opposite signal to cancel its own. Modems were then able to send at "full speed" in both directions at the same time, leading to the development of 4800 and 9600 bit/s modems.

Increases in speed have used increasingly complicated communications theory. 1200 and 2400 bit/s modems used the phase shift key (PSK) concept. This could transmit two or three bits per symbol. The next major advance encoded four bits into a combination of amplitude and phase, known as Quadrature Amplitude Modulation (QAM). Best visualized as a constellation diagram, the bits are mapped onto points on a graph with the x (real) and y (quadrature) coordinates transmitted over a single carrier. A constellation diagram is a representation of a signal modulated by a digital Modulation scheme such as Quadrature amplitude modulation or Phase-shift keying

The new V. 27ter and V. 32 standards were able to transmit 4 bits per symbol, at a rate of 1600 or 2400 baud, giving an effective bit rate of 4800 or 9600 bits per second. The carrier frequency was 1650 Hz. For many years, most engineers considered this rate to be the limit of data communications over telephone networks.

Error correction and compression

Operations at these speeds pushed the limits of the phone lines, resulting in high error rates. This led to the introduction of error-correction systems built into the modems, made most famous with Microcom's MNP systems. In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in Microcom Systems was a major Modem vendor during the 1980s although they were never as popular as the "big three" Hayes, U The MNP ( Microcom Networking Protocol) family of error-correcting protocols were commonly used on early high-speed (2400 bit/s and higher Modems Originally developed A string of MNP standards came out in the 1980s, each increasing the effective data rate by minimizing overhead, from about 75% theoretical maximum in MNP 1, to 95% in MNP 4. The new method called MNP 5 took this a step further, adding data compression to the system, thereby increasing the data rate above the modem's rating. Generally the user could expect an MNP5 modem to transfer at about 130% the normal data rate of the modem. MNP was later "opened" and became popular on a series of 2400-bit/s modems, and ultimately led to the development of V.42 and V.42bis ITU standards. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V. 42 and V. 42bis were non-compatible with MNP but were similar in concept: Error correction and compression.

Another common feature of these high-speed modems was the concept of fallback, allowing them to talk to less-capable modems. During the call initiation the modem would play a series of signals into the line and wait for the remote modem to "answer" them. They would start at high speeds and progressively get slower and slower until they heard an answer. Thus, two USR modems would be able to connect at 9600 bit/s, but, when a user with a 2400-bit/s modem called in, the USR would "fall back" to the common 2400-bit/s speed.

Breaking the 9. 6k barrier

In 1980 Gottfried Ungerboeck from IBM Zurich Research Laboratory applied powerful channel coding techniques to search for new ways to increase the speed of modems. Gottfried Ungerboeck received an electrical engineering degree in telecommunications in 1964 from Vienna University of Technology, and the Ph IBM Research, a division of IBM, is a research and advanced development organization and currently consists of eight locations throughout the world and hundreds of In Computer science, a channel code is a broadly used term mostly referring to the Forward error correction code and Bit interleaving in communication and His results were astonishing but only conveyed to a few colleagues^[1]. Finally in 1982, he agreed to publish what is now a landmark paper in the theory of information coding. By applying powerful parity check coding to the bits in each symbol, and mapping the encoded bits into a two dimensional "diamond pattern", Ungerboeck showed that it was possible to increase the speed by a factor of two with the same error rate. The new technique was called "mapping by set partitions" (now known as trellis modulation). In Telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient This new view was an extension of the "penny packing" problem and the related and more general problem of how to pack points into an N-dimension sphere such that they are far away from their neighbors. The greater two bit sequences are from one another, the easier it is to correct minor errors.

The industry was galvanized into new research and development. More powerful coding techniques were developed, commercial firms rolled out new product lines, and the standards organizations rapidly adopted to new technology. The "tipping point" occurred with the introduction of the SupraFax 14400 in 1991. Rockwell had introduced a new chipset supporting not only V. Rockwell International was the ultimate incarnation of a series of companies under the sphere of influence of Willard Rockwell, who had made his fortune after the invention and 32 and MNP, but the newer 14,400 bit/s V.32bis and the higher-compression V.42bis as well, and even included 9600 bit/s fax capability. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network Fax (short for facsimile, from Latin fac simile, "make similar" i Supra, then known primarily for their hard drive systems, used this chip set to build a low-priced 14,400 bit/s modem which cost the same as a 2400 bit/s modem from a year or two earlier (about US$300). A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device The product was a runaway best-seller, and it was months before the company could keep up with demand.

V. 32bis was so successful that the older high-speed standards had little to recommend them. USR fought back with a 16,800 bit/s version of HST, while AT&T introduced a one-off 19,200 bit/s method they referred to as V. 32ter (also known as V. 32 terbo), but neither non-standard modem sold well.

V. 34 / 28. 8k and 33. 8k

An ISA modem manufactured to conform to the V. 34 protocol.

Any interest in these systems was destroyed during the lengthy introduction of the 28,800 bit/s V.34 standard. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network While waiting, several companies decided to "jump the gun" and introduced modems they referred to as "V. FAST". In order to guarantee compatibility with V. 34 modems once the standard was ratified (1994), the manufacturers were forced to use more "flexible" parts, generally a DSP and microcontroller, as opposed to purpose-designed "modem chips". A microcontroller (also MCU or µC is a functional Computer system-on-a- chip.

Today the ITU standard V. 34 represents the culmination of the joint efforts. It employs the most powerful coding techniques including channel encoding and shape encoding. From the mere 4 bits per symbol (9. 6 kbit/s), the new standards used the functional equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2400 to 3429, to create 14. 4, 28. 8, and 33. 8 kbit/s modems. (See Tables 8 and 10 of the specification; maximum speed listed as "33 800". ) This rate is near the theoretical Shannon limit. In Information theory, the noisy-channel coding theorem establishes that however contaminated with noise interference a communication channel may be it is possible to communicate When calculated, the Shannon capacity of a narrowband line is Bandwidth * log₂(1 + P_u / P_n), with P_u / P_n the signal-to-noise ratio. Narrowband phone lines have a bandwidth from 300-3100 Hz, so using P_u / P_n = 100,000: capacity is approximately 35 kbit/s.

Without the discovery and eventual application of trellis modulation, maximum telephone rates would have been limited to 3429 baud * 4 bits/symbol == approximately 14 kilobits per second using traditional QAM.

Using digital lines and PCM (V. 90/92)

In the late 1990s Rockwell and U. S. Robotics introduced new technology based upon the digital transmission used in modern telephony networks. The standard digital transmission in modern networks is 64 kbit/s but some networks use a part of the bandwidth for remote office signaling (eg to hang up the phone), limiting the effective rate to 56 kbit/s DS0. Digital Signal 0 ( DS0) is a basic Digital signaling rate of 64 Kbit/s, corresponding to the capacity of one Voice-frequency -equivalent This new technology was adopted into ITU standards V. 90 and is common in modern computers. The 56 kbit/s rate is only possible from the central office to the user site (downlink) and in the United States, government regulation limits the maximum power output to only 53. 3 kbit/s. The uplink (from the user to the central office) still uses V. 34 technology at 33. 6k.

Later in V.92, the digital PCM technique was applied to increase the upload speed to a maximum of 48 kbit/s, but at the expense of download rates. For example a 48 kbit/s upstream rate would reduce the downstream as low as 40 kbit/s, due to echo on the telephone line. To avoid this problem, V. 92 modems offer the option to turn off the digital upstream and instead use a 33. 6 kbit/s analog connection, in order to maintain a high digital downstream of 50 kbit/s or higher. (See November and October 2000 update at http://www.modemsite.com/56k/v92s.asp ) V. 92 also adds two other features. The first is the ability for users who have call waiting to put their dial-up Internet connection on hold for extended periods of time while they answer a call. Dial-up Internet Access is a form of Internet access via Telephone lines The user's computer or Router uses an attached Modem connected to a The second feature is the ability to "quick connect" to one's ISP. This is achieved by remembering the analog and digital characteristics of the telephone line, and using this saved information to reconnect at a fast pace.

Using compression to exceed 56k

Today's V.42, V.42bis and V.44 standards allow the modem to transmit data faster than its basic rate would imply. V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network V90 redirects here For the automobile see Volvo V90. The ITU-T V-Series Recommendations on Data communication over the telephone network For instance, a 53. 3 kbit/s connection with V. 44 can transmit up to 53. 3*6 == 320 kbit/s using pure text. One problem is that the compression tends to get better and worse over time due to noise on the line, or due to the transfer of already-compressed files (ZIP files, JPEG images, MP3 audio, MPEG video). ^[2] At some points the modem will be sending compressed files at approximately 50 kbit/s, uncompressed files at 160 kbit/s, and pure text at 320 kbit/s, or any value in between. ^[3]

In such situations a small amount of memory in the modem, a buffer, is used to hold the data while it is being compressed and sent across the phone line, but in order to prevent overflow of the buffer, it sometimes becomes necessary to tell the computer to pause the datastream. This is accomplished through hardware flow control using extra pins on the modem–computer connection. The computer is then set to supply the modem at some higher rate, such as 320 kbit/s, and the modem will tell the computer when to start or stop sending data.

Compression by the ISP

As telephone-based 56k modems began losing popularity, some Internet Service Providers such as Netzero and Juno started using pre-compression to increase the throughput & maintain their customer base. As example, the Netscape ISP uses a compression program that squeezes images, text, and other objects at the server, just prior to sending them across the phone line. Netscape Communications (formerly known as Netscape Communications Corporation and commonly known as Netscape) is an American computer services company The server-side compression operates much more efficiently than the "on-the-fly" compression of V. 44-enabled modems. Typically website text is compacted to 4% thus increasing effective throughput to approximately 1300 kbit/s. The accelerator also precompresses Flash executables and images to approximately 30% and 12%, respectively.

The drawback of this approach is a loss in quality, where the graphics become heavily compacted and smeared, but the speed is dramatically improved such that webpages load in less than 5 seconds, and the user can manually choose to view the uncompressed images at any time. The ISPs employing this approach advertise it as "DSL speeds over regular phone lines" or simply "high speed dialup".

List of dialup speeds

Note that the values given are maximum values, and actual values may be slower under certain conditions (for example, noisy phone lines). ^[4] For a complete list see the companion article List of device bandwidths. This is a list of device bandwidths: the Net bit rate (or more informally Digital bandwidth) of some computer devices employing methods of data transport is quantified

Radio modems

Direct broadcast satellite, WiFi, and mobile phones all use modems to communicate, as do most other wireless services today. Direct broadcast satellite (DBS is a term used to refer to Satellite television broadcasts intended for home reception also referred to more broadly as direct-to-home Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used Modern telecommunications and data networks also make extensive use of radio modems where long distance data links are required. Mobile phones can be employed as data modems to form a wireless access point connecting a personal computer to the Internet (or some proprietary network) Such systems are an important part of the PSTN, and are also in common use for high-speed computer network links to outlying areas where fibre is not economical. The public switched telephone network ( PSTN) is the network of the world's public circuit-switched Telephone networks in much the same way that the Computer networking is the Engineering Discipline concerned with communication between Computer systems or devices Networking routers

Even where a cable is installed, it is often possible to get better performance or make other parts of the system simpler by using radio frequencies and modulation techniques through a cable. Coaxial cable has a very large bandwidth, however signal attenuation becomes a major problem at high data rates if a digital signal is used. Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all By using a modem, a much larger amount of digital data can be transmitted through a single piece of wire. Digital cable television and cable Internet services use radio frequency modems to provide the increasing bandwidth needs of modern households. Using a modem also allows for frequency-division multiple access to be used, making full-duplex digital communication with many users possible using a single wire. Frequency Division Multiple Access or FDMA is an Channel access method that is used by radio systems to share a certain Radio spectrum between multiple

Wireless modems come in a variety of types, bandwidths, and speeds. Wireless modems are often referred to as transparent or smart. They transmit information that is modulated onto a carrier frequency to allow many simultaneous wireless communication links to work simultaneously on different frequencies.

Transparent modems operate in a manner similar to their phone line modem cousins. Typically, they were half duplex, meaning that they could not send and receive data at the same time. A duplex Communication system is a system composed of two connected parties or devices which can communicate with one another in both directions Typically transparent modems are polled in a round robin manner to collect small amounts of data from scattered locations that do not have easy access to wired infrastructure. Transparent modems are most commonly used by utility companies for data collection.

Smart modems come with a media access controller inside which prevents random data from colliding and resends data that is not correctly received. Smart modems typically require more bandwidth than transparent modems, and typically achieve higher data rates. The IEEE 802.11 standard defines a short range modulation scheme that is used on a large scale throughout the world. IEEE 80211 is a set of standards for wireless local area network (WLAN computer communication developed by the IEEE LAN/MAN Standards Committee ( IEEE 802

WiFi and WiMax

Wireless data modems are used in the WiFi and WiMax standards, operating at microwave frequencies. Mobile phones can be employed as data modems to form a wireless access point connecting a personal computer to the Internet (or some proprietary network) Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used WiMAX, an approximate acronym of Worldwide Interoperability for Microwave Access, is a Telecommunications technology that provides for the wireless transmission Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0

WiFi is principally used in laptops for Internet connections (wireless access point) and wireless application protocol (WAP). Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used A laptop computer, also known as a notebook computer, is a small Personal computer designed for mobile use. In Computer networking, a wireless access point ( WAP or AP) is a device that allows wireless communication devices to connect to a Wireless network WAP is an open international Standard for Application layer network communications in a Wireless communication environment

Mobile modems & routers

External modems for mobile phone lines (GPRS and UMTS), are also known as datacards and cellular routers. General Packet Radio Service (GPRS is a Packet oriented Mobile Data Service available to users of Global System for Mobile Communications (GSM and Mobile phones can be employed as data modems to form a wireless access point connecting a personal computer to the Internet (or some proprietary network) Cellular routers (sometimes known as 3G Routers) are routers that provide shared Internet access by incorporating a cellular data Modem as WAN interfaces The datacard is a PC card, where a phone card is included, whereas a cellular router may or may not have an external datacard. In Computing, PC Card (originally '''PCMCIA''', or PCMCIA Card is the Form factor of a peripheral interface designed for Laptop computers A telephone card, calling card or phone card for short is a small card usually resembling a Credit card, used to pay for Telephone services Cellular routers (sometimes known as 3G Routers) are routers that provide shared Internet access by incorporating a cellular data Modem as WAN interfaces Most cellular routers do, except for the WAAV CM3 mobile broadband cellular router. WAAV (980 AM) is a Radio station broadcasting a News/Talk format Cellular routers (sometimes known as 3G Routers) are routers that provide shared Internet access by incorporating a cellular data Modem as WAN interfaces

Nowadays, there are USB modems with an integrated SIM cardholder (i. e, Huawei E220); that is, you only need a USB port and a modem to connect to the Internet. The Huawei E220 is a Huawei HSDPA access device ( ' Modem ') manufactured by Huawei and notable for using the USB interface

See : flat rate. A flat fee, also referred to as a flat rate or a linear rate, refers to a pricing structure that charges a single fixed fee for a service

Broadband

DSL modem

ADSL modems, a more recent development, are not limited to the telephone's "voiceband" audio frequencies. ADSL modem or DSL modem is a device used to connect a single Computer or Router to a DSL phone line in order to use an ADSL Asymmetric Digital Subscriber Line ( ADSL) is a form of DSL, a data communications technology that enables faster data transmission over Copper Telephone Some ADSL modems use coded orthogonal frequency division modulation (DMT). ADSL modem or DSL modem is a device used to connect a single Computer or Router to a DSL phone line in order to use an ADSL Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation (

Cable modems use a range of frequencies originally intended to carry RF television channels. A cable modem is a type of Modem that provides access to a data signal sent over the Cable television infrastructure Multiple cable modems attached to a single cable can use the same frequency band, using a low-level media access protocol to allow them to work together within the same channel. Typically, 'up' and 'down' signals are kept separate using frequency division multiple access. Frequency Division Multiple Access or FDMA is an Channel access method that is used by radio systems to share a certain Radio spectrum between multiple

New types of broadband modems are beginning to appear, such as doubleway satellite and powerline modems. The term broadband can have different meanings in different contexts This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Power line communication ( PLC) also known as power line carrier, mains communication, power line telecom ( PLT) or power line

Broadband modems should still be classed as modems, since they use complex waveforms to carry digital data. They are more advanced devices than traditional dial-up modems as they are capable of modulating/demodulating hundreds of channels simultaneously. Dial-up Internet Access is a form of Internet access via Telephone lines The user's computer or Router uses an attached Modem connected to a

Many broadband modems include the functions of a router (with Ethernet and WiFi ports) and other features such as DHCP, NAT and firewall features. A router ('rautər in the USA 'rutər in the UK and Ireland, or either pronunciation in Australia and Canada is a Computer whose software and hardware are usually Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used In Computer networking network address translation (NAT is the process of modifying Network address information in datagram packet headers while in transit across A firewall is an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system

When broadband technology was introduced, networking and routers were unfamiliar to consumers. However, many people knew what a modem was as most internet access was through dialup. Due to this familiarity, companies started selling broadband modems using the familiar term "modem" rather than vaguer ones like "adapter" or "transceiver".

Most modems must be configured properly before they can use a router. This configuration is known as bridge mode.

Deep-space telecommunications

Many modern modems have their origin in deep-space telecommunications systems of the 1960s.

Differences with deep space telecom modems vs landline modems

• digital modulation formats that have high doppler immunity are typically used
• waveform complexity tends to be low, typically binary phase shift keying
• error correction varies mission to mission, but is typically much stronger than most landline modems

Voice modem

Voice modems are regular modems that are capable of recording or playing audio over the telephone line. They are used for telephony applications. In Telecommunication, telephony (təˈlɛfəni or teh-LEH-fuh-nee encompasses the general use of equipment to provide voice communication over distances specifically See Voice modem command set for more details on voice modems. Main article Modem Voice modem is a term commonly used to describe an analog telephone data modem with a built-in capability of transmitting This type of modem can be used as FXO card for Private branch exchange systems (compare V.92). In telecommunications a Foreign Exchange Office, or FXO, is a Telephone signaling interface that receives POTS, or "plain old telephone service" A private branch exchange (PBX is a Telephone exchange that serves a particular business or office as opposed to one that a Common carrier or telephone company

Popularity

A CEA study in 2006 found that dial-up Internet access is on a notable decline in the U. The Consumer Electronics Association (CEA is the Trade organization for the Consumer electronics industry in the United States. S. In 2000, dial-up Internet connections accounted for 74% of all U. S. residential Internet connections. The US demographic pattern for (dialup modem users per capita) has been more or less mirrored in Canada and Australia for the past 20 years.

Dialup modem use in the US had dropped to 60% by 2003, and currently (2006) stands at 36%. Voiceband modems were once the most popular means of Internet access in the U. The Internet is a global system of interconnected Computer networks S. , but with the advent of new ways of accessing the Internet, the traditional 56K modem is losing popularity.

See also

• Chapter Hayes-compatible Modems and AT Commands of the Serial Data Communications Programming Wikibook
• 56 kbit/s line
• Advanced Configuration Power Interface (ACPI)
• Automatic negotiation (or "handshake")
• BBN Technologies (developed the first model in 1963)
• Broadband: satellite modem, ADSL, cablemodem, PLC. Wikibooks (previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks) is a Wikimedia Foundation Wiki for the creation of A 56 kbit/s line is a digital connection capable of carrying 56 Kilobits per second ( Kbit/s) or 56000 Bit/s, the Data rate of a normal single The Advanced Configuration and Power Interface ( ACPI) specification an open industry standard first released in December 1996 (developed by HP, Intel In Information technology, Telecommunications, and related fields handshaking is an automated process of negotiation that dynamically sets parameters of The term broadband can have different meanings in different contexts A satellite modem or sat modem is a Modem used to establish Data transfers using a Communications satellite as a Relay. Asymmetric Digital Subscriber Line ( ADSL) is a form of DSL, a data communications technology that enables faster data transmission over Copper Telephone A cable modem is a type of Modem that provides access to a data signal sent over the Cable television infrastructure Power line communication ( PLC) also known as power line carrier, mains communication, power line telecom ( PLT) or power line
• Command and Data modes (modem)
• Dial up
• Driver
• DHCP
• Ethernet
• Hayes command set
• INF file
• TCP/IP
• ITU V-series telephone network modem standards, including V.92
• K56flex
• Modulation (for a fuller list of modulation techniques)
• Plug-and-Play
• RJ-11
• Wake-Up on Ring (WOR)
• X2 (Chipset)
• Zeroconf

References

External links

Standards Organizations and modem protocols

• International Telecommunications Union ITU: Data communication over the telephone network
• Federal Communications Commission TELECOMMUNICATION: PART 64_MISCELLANEOUS RULES RELATING TO COMMON CARRIERS
• 56k
• V.92
• Columbia University - Protocols Explained - no longer available, archived version
• Basic handshakes & modulations - V. 22, V. 22bis, V. 32 and V. 34 handshakes

General modem info (drivers, chipsets, etc. )

• A very good primer about modems
• Installing, testing, troubleshooting & tweaking modems
• Costmo Modem Site
• How Stuff Works - Modems
• ModemHelp.Net
• ModemHelp.org
• Modem-Help.co.uk
• ModemSite.com
• Modem Tutorial - what is a modem - How modems can be applied for machine telemetry applications

Other

• Modems.com - Site operated by Zoom and is mainly a sales pitch for v. 92
• www.asteriskguru.com - Tutorial Asterisk and Analog Interface Cards, User Comments
• Modem initialisation string

Telephone network modem standards
ITU V-Series | V.92 | K56flex | X2 | MNP | Hayes command set