Modem: Difference between revisions

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{{Short description|Device that modulates an analog carrier signal to encode digital information}}

A '''modem''' (a [[portmanteau|portmanteau word]] constructed from '''mod'''ulator and '''dem'''odulator) is a [[device]] that [[modulation|modulates]] a [[carrier wave|carrier]] [[Signal_(information_theory)|signal]] to encode [[digital]] information, and also [[demodulation|demodulates]] such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital [[data]].

{{Redirect-distinguish|Computer modem|Computer Modern}}

{{For-multi|the French political party known as Modem|Democratic Movement (France)|the ancient Hebrew city|Modi'in-Maccabim-Re'ut}}

[[File:Analogue modem - acoustic coupler.jpg|thumb|[[Acoustic coupler]] modems used a telephone handset as the audio medium, with the user dialing the desired number and then pressing the handset into the modem to complete the connection. These systems generally operated at a speed of 300 bits per second.]]

The most familiar example of a modem turns the digital '1s and 0s' of a personal computer into sounds that can be transmitted over the [[telephone line]]s of Plain Old Telephone System ([[Plain old telephone service|POTS]]), and once received on the other side, converts those sounds back into 1s and 0s.

{{Modulation techniques}}

Far more exotic modems are used by internet users every day. In [[telecommunications]], "radio modems" transmit [[serial communications|repeating frames of data]] at very high data rates over [[microwave]] radio links. Some microwave modems transmit more than a hundred million bits per second.

A '''modulator-demodulator''', commonly referred to as a '''modem''', is a [[computer hardware]] device that converts [[Digital data|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 diode|LED]]s to [[radio]].

''[[Wavelength division multiplexing|Optical modem]]s'' transmit data over [[optic fiber]]s. Most intercontinental data links now use optic modems transmitting over [[submarine communications cable|undersea optical fibers]]. Optic modems usually use interferometric filters called [[etalon]]s to separate different colors of light, and then individually turn the pulses of each color of light into electronic digital data streams. Optical modems routinely have data rates in excess of a billion (1x10^9) bits per second. Their bandwidths are currently limited by the thermal expansion of the etalons. Heat changes an etalon's size and thus its frequency.

Early modems were devices that used audible sounds suitable for transmission over traditional [[telephone]] systems and [[leased line]]s. 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 bit/s for asynchronous dial connections, 4,800 bit/s for synchronous leased line connections and 35 kbit/s for synchronous conditioned leased lines were available. By the 1980s, less expensive 1,200 and 2,400 bit/s dialup modems were being released, and modems working on radio and other systems were available. As device sophistication grew rapidly in the late 1990s, telephone-based modems quickly exhausted the available [[Bandwidth (computing)|bandwidth]], reaching 56 kbit/s.

Modems can be used over any means of transmitting analog signals, from driven [[diode]]s to [[radio]].

The rise of public use of the [[internet]] during the late 1990s led to demands for much higher performance, leading to the move away from audio-based systems to entirely new encodings on [[cable television]] lines and short-range signals in [[subcarrier]]s on telephone lines. The move to [[cellular telephone]]s, especially in the late 1990s and the emergence of [[smartphone]]s in the 2000s led to the development of ever-faster radio-based systems. Today, modems are ubiquitous and largely invisible, included in almost every mobile computing device in one form or another, and generally capable of speeds on the order of tens or hundreds of megabytes per second.

==History==

[[Image:BellSystemDataphone1957.jpg|thumb|200px|1957 AT&T Dataphone]]Modems were first introduced as a part of the [[Semi Automatic Ground Environment|SAGE]] air-defense system in the 1950s, connecting terminals located at various airbases, radar sites and command-and-control centers to the SAGE director centers scattered around the US and Canada. SAGE ran on dedicated communications lines, but the devices at either end were otherwise similar in concept to today's modems. [[IBM]] was the primary contractor for both the computers and the modems used in the SAGE system. A few years later a chance meeting between the CEO of [[American Airlines]] and a regional manager of IBM led to a "mini-SAGE" being developed as an automated airline ticketing system. In this case the terminals were located at ticketing offices, tied to a central computer that managed availability and scheduling. The system, known as [[Sabre (computer system)|Sabre]], is the distant parent of today's SABRE system. The [[AT&T]] Dataphone was another pioneering early data-transfer service using telephone lines to transmit business information, such as inventory levels.

== Speeds ==

By the early 1960s commercial computer use had bloomed, due in no small part to the developments above, and in 1962 [[AT&T]] released the first commercial modem, the [[Bell 103]]. Using [[frequency-shift keying]], where two tones are used to represent the 1's and 0's of digital data, the 103 had a transmission rate of 300 bit/s. Only a short time later they released the [[Bell 212]] modem, switching to the more reliable [[phase-shift keying]] system and increasing the data rate to 1200 bit/s. The similar [[Bell 201]] system used both sets of signals (send and receive) on 4-wire [[leased line]]s for 2400 bit/s operation.

Modems are frequently classified by the maximum amount of data they can send in a given [[Time unit|unit of time]], usually expressed in [[bits per second]] (symbol '''bit/s''', sometimes abbreviated "bps") or rarely in [[bytes per second]] (symbol '''B/s'''). Modern broadband modem speeds are typically expressed in megabits per second (Mbit/s).

Historically, modems were often classified by their [[symbol rate]], measured in [[baud]]. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the [[ITU-T V.21]] standard used [[Frequency-shift keying#Audio FSK|audio frequency-shift keying]] with two possible frequencies, corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original [[ITU-T V.22]] standard, which could transmit and receive four distinct symbols (two bits per symbol), transmitted 1,200 bits by sending 600 symbols per second (600 baud) using [[phase-shift keying]].

The next major advance in modems was the Hayes Smartmodem, introduced in 1981 by [[Hayes Communications]]. The Smartmodem was a simple 300 bit/s modem using the Bell 103 signaling standards, but attached to a small controller that let the computer send commands to it to operate the phone line. The basic [[Hayes command set]] remains the basis for computer control of most modern modems.

Many modems are variable-rate, permitting them to be used over a medium with less than ideal characteristics, such as a telephone line that is of poor quality or is too long. This capability is often adaptive so that a modem can discover the maximum practical transmission rate during the connect phase, or during operation.

Part of the reason for the advance to line-connected modems like the Smartmodem, rather than acoustically-coupled modems, was internationally widespread deregulation of telephone companies. At one time, any equipment electrically connected to most telephone lines had to belong to the telephone company. The [[acoustic coupler]], despite inherent speed and reliability limitations, would allow a user's computer to communicate through a telephone which was rented from the telephone company.

[[File:Australian-modems.jpg|center|thumb|800x800px|Collection of modems once used in Australia, including dial-up, DSL, and cable modems]]

[[Image:Acoustic_coupler_20041015_175456_1.jpg|thumb|275px|Acoustically coupled modem]]

Prior to the Smartmodem, modems almost universally required a two-step process to activate a connection: first, manually dial the remote number on a standard phone handset, then plug the handset into a modem-attached [[acoustic coupler]], a device with two rubber cups for the handset that converted between the audio signals and the electrical modem signals. With the Smartmodem, the acoustic coupler was eliminated by plugging the modem directly into a modular phone set or wall jack, and the computer was "smart" enough to bypass the phone and dial the number directly. These changes greatly simplified installation and operation of [[Bulletin board system|bulletin board systems (BBS)]].

== Overall history ==

Modems stayed at about these rates into the 1980s. A 2400 bit/s system very similar to the [[Bell 212]] signalling was introduced in the US, and a slightly different, and incompatible, one in Europe. By the late 1980s most modems could support all of these standards, and 2400 bit/s was becoming common. A huge number of other standards were also introduced for special-purpose situations, 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, where the user's terminals spent the majority of their time receiving information. The modem in the Minitel terminal thus operated at 1200 bit/s for reception, and 75 bit/s for sending commands back to the [[server]]s.

Modems grew out of the need to connect [[teleprinter]]s over ordinary phone lines instead of the more expensive leased lines which had previously been used for [[current loop]]–based teleprinters and automated [[telegraph]]s. The earliest devices which satisfy the definition of a modem may have been the [[multiplexer]]s used by [[News agency|news wire services]] in the 1920s.<ref>{{Cite web |title=History of the Modem |url=https://www.thoughtco.com/history-of-the-modem-4077013 |website=ThoughtCo.com |first=Mary |last=Bellis |date=2017-12-31 |access-date=2021-04-05 }}</ref>

In 1941, the [[Allies of World War II|Allies]] developed a voice [[encryption]] system called [[SIGSALY]] which used a [[vocoder]] to digitize speech, then encrypted the speech with one-time pad and encoded the digital data as tones using frequency shift keying. This was also a digital modulation technique, making this an early modem.<ref>{{Cite web|title=National Security Agency Central Security Service > About Us > Cryptologic Heritage > Historical Figures and Publications > Publications > WWII > Sigsaly – The Start of the Digital Revolution|url=https://www.nsa.gov/about/cryptologic-heritage/historical-figures-publications/publications/wwii/sigsaly-start-digital/|access-date=2020-08-13|website=NSA.gov}}</ref>

These sorts of solutions were useful in a number of situations where one side would be sending more data than the other. In addition to a number of "medium-speed" standards like Minitel, four US companies became famous for high-speed versions of the same concept. [[Microcom Systems]] introduced their [[MNP]], Hayes their [[Ping Pong]], [[U.S. Robotics|USR]] had their [[HST]] protocol, and [[Telebit]] used software to increase performance. In all of these cases the high-speed line was set to 9600 bit/s, and the low-speed line to between 75 and 300 bit/s. Each company carved out a niche in the market, Telebit was huge in the universities due to their direct support of [[UUCP]] protocols in the modem itself, Microcom became common in commercial settings, and USR was huge among BBS operators (as they could download [[Fidonet]] messages more quickly), but the Hayes standard never caught on. In all of these cases there was a well defined high-speed and low-speed direction, but such a split was not so obvious for users who were uploading and downloading files in the same session, and these solutions were rarely used by them.

Commercial modems largely did not become available until the late 1950s, when the rapid development of computer technology created demand for a method of connecting computers together over long distances, resulting in the [[AT&T Corporation]] and then other businesses producing an increasing number of computer modems for use over both switched and leased telephone lines.

Operations at these speeds pushed the limits of the phone lines, and would have been generally very error-prone. This led to the introduction of error correction systems built into the modems, made most famous with Microcom's MNP systems. A string of MNP standards came out in the 1980s, each slowing the effective data rate by a smaller amount each time, from about 25% in MNP1, to 5% in MNP4. MNP5 took this a step further, adding compression to the system, thereby actually increasing the data rate - in general use the user could expect an MNP modem to transfer at about 1.3 times the normal data rate of the modem. MNP was later "opened" and became popular on a series of 2400 bit/s modems, although it was never widespread.

Later developments would produce modems that operated over [[Cable Internet access|cable television lines]], [[Power-line communication|power lines]], and various [[#Radio|radio technologies]], as well as modems that achieved [[Broadband|much higher speeds]] over telephone lines.

Another common feature of these high-speed modems was the concept of [[Fall back and forward|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 another user with a 2400 bit/s modem called in, the USR would "fall back" to the common 2400 bit/s speed. Without such a system the operator would be forced to have multiple phone lines for high and low speed use.

==Dial-up==

==Long haul modems==

A dial-up modem transmits computer data over an ordinary [[Public switched telephone network|switched]] telephone line that has not been designed for data use. It was once a widely known technology, mass-marketed globally [[Dial-up Internet access|dial-up internet access]]. In the 1990s, tens of millions of people in the United States alone used dial-up modems for internet access.<ref>{{Cite web|last=Manjoo|first=Farhad|date=2009-02-24|title=The unrecognizable Internet of 1996.|url=https://slate.com/technology/2009/02/the-unrecognizable-internet-of-1996.html|access-date=2020-08-10|website=Slate Magazine|language=en}}</ref>

In the 1960s, Bell began to digitize the telephone system, and developed early high-speed radio modems for this purpose. Once digital long-haul networks were in place, they were leased for every other purpose.

Dial-up service has since been largely superseded by [[Broadband Internet|broadband internet]],<ref>{{Cite web|last=Brenner|first=Joanna|title=3% of Americans use dial-up at home|url=https://www.pewresearch.org/fact-tank/2013/08/21/3-of-americans-use-dial-up-at-home/|access-date=2020-08-10|website=Pew Research Center|date=21 August 2013 |language=en-US}}</ref> such as [[DSL]].

Optic fiber manufacturing was perfected in the 1980s, and optic modems were first invented for these early systems. The first systems simply used [[light emitting diode]]s and [[PIN diode]]s. Faster modulation was quickly adopted for long-haul networks. In the [[1990s]], multispectral optical modems were adopted as well.

===Echo cancellationHistory ===

[[Echo cancellation]] was the next major advance in modem design. Normally the phone system sends a small amount of the outgoing signal, called sidetone, back to the earphone, in order to give the user some feedback that their voice is indeed being sent. However this same signal can confuse the modem, is the signal it is "hearing" from the remote modem, or its own signal being sent back to itself? This was the reason for splitting the signal frequencies into answer and originate; if you received a signal on your own frequency set, you simply ignored it. Even with improvements to the phone system allowing for higher speeds, this splitting of the available phone signal [[bandwidth]] still imposed a half-speed limit on modems.

==== 1950s ====

Echo cancellation was a way around this problem. By using the phone system's timing, a slight delay, it was possible for the modem to tell if the received signal was from itself or the remote modem. As soon as this happened the modems were able to send at "full speed" in both directions at the same time, opening the market to a slew of 9600 bit/s bidirectional modems in the late 1980s. These earlier systems were not very popular due to their price, but by the early 1990s the prices started falling. The "breaking point" occurred with the introduction of the SupraFax 14400 in 1991, which cost the same as a 2400 bit/s modem from a year or two earlier (about $300US), but ran at the latest 14,400 bit/s rate (14.4 kbit/s) and also included [[fax]] capability. Over the next few years the speed increased to 28.8 kbit/s, then to 33.6 kbit/s, along with a slew of one-off non-standards like AT&T's 19.2 kbit/s system.

[[File:TeleGuide-terminal.jpg|thumb|TeleGuide terminal]]

Mass production of telephone line modems in the United States began as part of the [[Semi Automatic Ground Environment|SAGE]] air-defense system in 1958, connecting terminals at various airbases, radar sites, and command-and-control centers to the SAGE director centers scattered around the United States and [[Canada]].

The last major advance in modem design was the [[56 kbit/s]] standard, introduced in the late 1990s. This standard is similar to the earlier high-speed/low-speed systems rejected by users in the 1980s, but with the increasing use of the internet, which is largely "read only", the small sacrifice for higher speeds made sense once again.

Shortly afterwards in 1959, the technology in the SAGE modems was made available commercially as the [[Bell 101]], which provided 110 bit/s speeds. Bell called this and several other early modems "datasets".{{anchor|Dataset}}

==== 1960s ====

Some early modems were based on [[touch-tone]] frequencies, such as Bell 400-style touch-tone modems.<ref>

==Narrowband==

Don Lancaster.

[https://www.tinaja.com/ebooks/tvtcb.pdf "TV Typewriter Cookbook"].

1976.

([[TV Typewriter]]).

Section "400-Style (Touch-Tone) Modems".

pp. 177–178.

</ref>

The [[Bell 103 modem|Bell 103A]] standard was introduced by [[AT&T]] in 1962. It provided full-duplex service at 300&nbsp;bit/s over normal phone lines. [[Frequency-shift keying]] was used, with the call originator transmitting at 1,070 and 1,270&nbsp;[[Hertz|Hz]] and the answering modem transmitting at 2,025 and 2,225&nbsp;Hz.<ref>{{Cite web|last=Internet|first=Tamsin Oxford 2009-12-26T11:00:00 359Z|title=Getting connected: a history of modems|url=https://www.techradar.com/news/internet/getting-connected-a-history-of-modems-657479|access-date=2018-12-12|website=TechRadar|date=26 December 2009|language=EN-GB}}</ref>

[[Image:Motorola modem 28k.jpg|thumb|270px|right|28.8kbps [[Serial port|serial-port]] modem from [[Motorola]]]]

The 103 modem would eventually become a de facto standard once third-party (non-AT&T) modems reached the market, and throughout the 1970s, independently made modems compatible with the Bell 103 de facto standard were commonplace.<ref>{{Cite web|date=1969-03-05|title=Computerworld|url=https://archive.org/details/computerworld19699|access-date=2020-08-13|website=Internet Archive|language=en}}</ref> Example models included the [[Novation CAT]] and the [[Anderson-Jacobson]]. A lower-cost option was the [[Pennywhistle modem]], designed to be built using readily available parts.<ref>{{Cite web|title=Pennywhistle 103, modem kit 1976: : Free Download, Borrow, and Streaming|url=https://archive.org/details/TNM_Pennywhistle_103_modem_kit_1976_20180226_0229|access-date=2020-08-13|website=Internet Archive|language=en}}</ref>

A standard modem of today is what would have been called a "smart modem" in the 1980s. They contain two functional parts: an analog section for generating the signals and operating the phone, and a digital section for setup and control. This functionality is actually incorporated into a single chip, but the division remains in theory.

Teletype machines were granted access to remote networks such as the [[Teletypewriter eXchange|Teletypewriter Exchange]] using the Bell 103 modem.<ref>{{Cite web|date=1967|title=Bell 103A Interface Specifications|url=http://bitsavers.trailing-edge.com/communications/westernElectric/modems/103A_Interface_Specification_Feb67.pdf}}</ref> AT&T also produced reduced-cost units, the originate-only 113D and the answer-only 113B/C modems.

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 to hang up the phone is sent. One problem with this method of operation is that it is not really possible for the modem to know if a string is a command or data. Funny things happen when they get confused.

==== 1970s ====

The commands themselves are typically from the [[Hayes command set]], although that term is somewhat misleading. The original Hayes commands were useful for 300 bit/s operation only, and then extended for their 1200 bit/s modems. Hayes was much slower upgrading to faster speeds however, leading to a proliferation of command sets in the early 1990s as each of the high-speed vendors introduced their own command styles. 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", invariably supporting a rapidly converging command set. We call this the Hayes command set even today, although in this use the terminology is misleading: the command set in question has three or four times the numbers of commands.

The ''201A'' ''Data-Phone'' was a synchronous modem using two-bit-per-symbol [[phase-shift keying]] (PSK) encoding, achieving 2,000&nbsp;bit/s half-duplex over normal phone lines.<ref>{{Cite web|date=1969-11-01|title=Lockheed MAC 16 options reference manual|url=https://archive.org/details/bitsavers_lockheedmarenceManualInterimNov69_8493760|access-date=2020-08-14|website=Internet Archive|language=en}}</ref> In this system the two tones for any one side of the connection are sent at similar frequencies as in the 300&nbsp;bit/s systems, but slightly out of phase.

In early 1973, [[Racal|Vadic]] introduced the ''VA3400'' which performed full-duplex at 1,200&nbsp;bit/s over a normal phone line.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=YjQZ-J-JM7cC&q=computerworld%20modem&pg=PA1|title=Computerworld|date=1976-09-27|publisher=IDG Enterprise|language=en}}</ref>

The 300 bit/s modems used [[frequency-shift keying]] to send data. In this system the stream of 1's and 0's in computer data it translated into sounds which can be easily sent on the phone lines. In the Bell 103 system the ''originating'' modem sends 0's by playing a 1070 Hz tone, and 1's at 1270 Hz, with the ''receiving'' modem putting its 0's on 2025 Hz and 1's 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 [[harmonic]]s of each other. In early systems the choice of answer or originate was selected by a switch on the front of the modem, but as time went on the Smartmodems would assume originate if asked to dial, and answer if asked to answer the phone.

In November 1976, AT&T introduced the 212A modem, similar in design, but using the lower frequency set for transmission. It was not compatible with the VA3400,<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=POjXwPy5eBUC&q=computerworld%20vadic%20212a%20incompatible&pg=PA43|title=Computerworld|date=1986-02-17|publisher=IDG Enterprise|language=en}}</ref> but it would operate with 103A modem at 300&nbsp;bit/s.

In the 1200 bit/s and faster systems, [[phase-shift keying]] was used. 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, 1's and 0's 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 bit/s modems with "tricky" signalling.

In 1977, Vadic responded with the VA3467 triple modem, an answer-only modem sold to computer center operators that supported Vadic's 1,200-bit/s mode, AT&T's 212A mode, and 103A operation.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=5OsHzHowTLIC&q=computerworld%20vadic%203467&pg=PA1|title=Computerworld|date=1977-11-14|publisher=IDG Enterprise|language=en}}</ref>

It was at this point that the difference between [[baud]] and [[bit per second]] became real. Baud refers to the signaling rate of a system, in a 300 bit/s modem the signals sent one bit per signal, so the data rate and signalling rate was the same. In the 1200 bit/s systems this was no longer true, the modems were actually 600 baud. This led to a series of [[flame war]]s on the BBSes of the 80s.

[[File:Hayes 300 Baud Smartmodem 02.jpg|thumb|The original 300-baud Hayes Smartmodem]]

Increases in speed have since used increasingly complicated communications theory. The Bell 208 introduced the 8 phase shift key concept. This could transmit three bits per signaling instance (baud.) The next major advance was introduced by Codex Co. in the late 1960's. Here the bits were encoded into a combination of amplitude and phase. Best visualized as a two dimensional "eye pattern", the bits are mapped onto points on a graph with the x (real) and y (quadrature) coordinates transmitted over a single carrier. This technique became very effective and was incorporated into an international standard named V.29, by the CCITT (now ITU) arm of the United Nations. The standard was able to transmit 4 bits per signalling interval of 2400 Hz. giving an effective bit rate of 9600 bits per second. For many years, most considered this rate to be the limit of data communications over telephone networks.

==== 1980s ====

In 1980 Godfried Ungerboek from IBM applied powerful channel coding techniques to search for new ways to increase the speed of modems. His results were astonishing but only conveyed to a few colleagues. 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 "eye pattern", Ungerboek 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. 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 (so that noise can not confuse the receiver.)

A significant advance in modems was the [[Hayes Microcomputer Products#The Smartmodem|Hayes Smartmodem]], introduced in 1981. The Smartmodem was an otherwise standard 103A 300&nbsp;bit/s direct-connect modem, but it introduced a command language which allowed the computer to make control requests, such as commands to dial or answer calls, over the same RS-232 interface used for the data connection.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=KbM9-s49yCMC&q=computerworld%20hayes%20smartmodem%201981&pg=RA1-PA42|title=Computerworld|date=1981-04-27|publisher=IDG Enterprise|language=en}}</ref> The command set used by this device became a de facto standard, the [[Hayes command set]], which was integrated into devices from many other manufacturers.

Automatic dialing was not a new capability{{Mdash}}it had been available via separate [[#Automatic Calling Units / Dialers|Automatic Calling Units]], and via modems using the [[X.21]] interface<ref>{{Cite book|title=Practical data communications : modems, networks and protocols : Jennings, Fred : Free Download, Borrow, and Streaming|url=https://archive.org/details/practicaldatacom00jenn|access-date=2020-08-14|via=Internet Archive|year=1986|isbn=9780632013067|language=en|last1=Jennings|first1=Fred|publisher=Blackwell Scientific }}</ref>{{Mdash}}but the Smartmodem made it available in a single device that could be used with even the most minimal implementations of the ubiquitous RS-232 interface, making this capability accessible from virtually any system or language.<ref>{{Cite web|title=Compute! Magazine Issue 012 : Free Download, Borrow, and Streaming|url=https://archive.org/details/1981-05-compute-magazine|access-date=2020-08-14|website=Internet Archive|date=May 1981|language=en}}</ref>

The industry was galvanized into new research and development. More powerful coding techniques were developed and commercial firms rolled out new product lines, and the standards organizations rapidly adopted to new technology. 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 16 points per symbol, V.34 uses over 1000 points and very sophisticated algorithms to achieve 33.6 kbit/s.

The introduction of the Smartmodem made communications much simpler and more easily accessed. This provided a growing market for other vendors, who licensed the Hayes patents and competed on price or by adding features.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=hCqdKWvxFT4C&q=%22computerworld%22%20%22hayes%20compatible%22&pg=PA61-IA6|title=Computerworld|date=1987-03-30|publisher=IDG Enterprise|language=en}}</ref> This eventually led to legal action over use of the patented Hayes command language.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=mUSIMiurpfYC&q=%22computerworld%22%20%22hayes%20compatible%22&pg=PP137|title=Computerworld|year=1987|publisher=IDG Enterprise|language=en}}</ref>

In the late 1990's 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 signalling (E.G. hang up the phone.) So the effective rate is 56 kbit/s [[DS0]]. This rate is possible only from the central office to the user site (downlink). The uplink (from the user to the central office still uses V.34 technology. This new technology was adopted into ITU standards V.90 and V.92 and are common in modern computers.

Dial modems generally remained at 300 and 1,200&nbsp;bit/s (eventually becoming standards such as [[ITU-T V.21|V.21]] and [[ITU-T V.22|V.22]]) into the mid-1980s.

Commodore's 1982 ''VicModem'' for the [[VIC-20]] was the first modem to be sold under $100, and the first modem to sell a million units.<ref>{{Cite journal |last=Herzog |first=Marty |date=January 1988 |title=Neil Harris |journal=Fictioneer Books. |volume=Comics Interview |issue= 54 |pages=41–51}}</ref>

It is guessed that this rate is near the theoretical [[Shannon limit]]. Higher speeds are possible but may be due more to improvements in the underlying phone system than anything in the technology of the modems themselves.

In 1984, [[ITU-T V.22bis|V.22bis]] was created, a 2,400-bit/s system similar in concept to the 1,200-bit/s Bell 212. This bit rate increase was achieved by defining four or sixteen distinct symbols, which allowed the encoding of two or four bits per symbol instead of only one. By the late 1980s, many modems could support improved standards like this, and 2,400-bit/s operation was becoming common.

Software is as important to the operation of the modem today as the hardware. Even with the improvements in the performance of the phone system, modems still lose a considerable amount of data due to noise on the line. The MNP standards were originally created to automatically fix these errors, and later expanded to compress the data at the same time. Today's [[v.42]] and [[v.42bis]] fill these roles in the vast majority of modems, and although later MNP standards were released, they are not common.

Increasing modem speed greatly improved the responsiveness of online systems and made [[file transfer]] practical. This led to rapid growth of [[online service]]s with large file libraries, which in turn gave more reason to own a modem. The rapid update of modems led to a similar rapid increase in BBS use.

With such systems it is possible for the modem to transmit data faster than its basic rate would imply. For instance, a 2400 bit/s modem with v.42bis can transmit up to 9600 bit/s, at least in theory. One problem is that the compression tends to get better and worse over time, at some points the modem will be sending the data at 4000 bit/s, and others at 9000 bit/s. In such situations it becomes necessary to use '''hardware flow control''', extra pins on the modem-computer connection to allow the computers to signal data flow. The computer is then set to supply the modem at some higher rate, in this example at 9600 bit/s, and the modem will tell the computer to stop sending if it cannot keep up. A small amount of memory in the modem, a buffer, is used to hold the data while it is being sent.

The introduction of [[microcomputer]] systems with internal [[expansion slot]]s made small internal modems practical. This led to a series of popular modems for the [[S-100 bus]] and [[Apple II]] computers that could directly dial out, answer incoming calls, and hang up entirely from software, the basic requirements of a [[bulletin board system]] (BBS). The seminal [[CBBS]] for instance was created on an S-100 machine with a Hayes internal modem, and a number of similar systems followed.

Almost all modern modems also do double-duty as a [[fax]] machine as well. Digital faxes, introduced in the 1980s, are simply a particular [[image format]] sent over a high-speed (9600/1200 bit/s) modem. 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.

===Winmodem ===

A '''[[Winmodem]]''' or '''[[Softmodem]]''' is a stripped-down modem for [[Microsoft Windows|Windows]] that replaces tasks traditionally handled in [[hardware]] with [[software]]. In this case the computer's built-in sound hardware is used to generate the tones normally handled by the analog portion of the modem. A small piece of hardware is then used to connect the sound hardware to the phone line. Modern computers often include a very simple [[card slot]], the [[Communications and Networking Riser]] slot (CNR), to lower the cost of connecting it up. The CNR slot includes pins for sound, power and basic signalling, instead of the more expensive [[PCI]] slot normally used. Winmodems are often cheaper than traditional modems, since they have fewer hardware components. One downside of a Winmodem is that the software generating the modem tones is not that 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 with WinModems is lack of flexibility, due to their strong tie to the underlying operating system. A given Winmodem might not be supported by other operating systems (such as [[Linux]]), because their manufacturers may neither support the other operating system nor provide enough technical data to create an equivalent driver. A Winmodem might not even work (or work well) with a later version of Microsoft Windows, if its driver turns out to be incompatible with that later version of the operating system.

[[Echo cancellation#Modems|Echo cancellation]] became a feature of modems in this period, which allowed both modems to ignore their own reflected signals. This way both modems can simultaneously transmit and receive over the full spectrum of the phone line, improving the available bandwidth.<ref>{{cite book |last=Tretter |first=Steven A. |year=1995 |title=Communication System Design Using DSP Algorithms |url=https://link.springer.com/chapter/10.1007/978-1-4757-9763-3_15 |publisher=Springer, Boston, MA |pages=153–159 |doi=10.1007/978-1-4757-9763-3_15 |isbn=978-0-306-45032-7}}</ref>

[[Apple Computer|Apple's]] [[GeoPort]] modems from the second half of the 1990s were similar, and are generally regarded as having been a bad move. 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.

Additional improvements were introduced by [[quadrature amplitude modulation]] (QAM) encoding, which increased the number of bits per symbol to four through a combination of phase shift and amplitude.

Today's modern audio modems ([[ITU-T]] [[V.92]] standard) closely approach the [[Shannon capacity]] of the [[PSTN]] telephone channel. They are [[plug-and-play]] [[fax]]/data/voice modems (broadcast voice messages and records [[touch tone]] responses).

Transmitting at 1,200&nbsp;baud produced the 4,800&nbsp;bit/s [[V.27ter]] standard, and at 2,400&nbsp;baud the 9,600&nbsp;bit/s [[ITU-T V.32|V.32]]. The [[carrier frequency]] was 1,650&nbsp;Hz in both systems.

==Wireless "modems"==

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.

The introduction of these higher-speed systems also led to the development of the digital [[fax]] machine during the 1980s. While early fax technology also used modulated signals on a phone line, digital fax used the now-standard digital encoding used by computer modems. This eventually allowed computers to send and receive fax images.

Transparent modems operate in a manner similar to their phone line modem cousins. Typically, they are half duplex, meaning that they cannot send and receive data at the same time. 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.

==== 1990s ====

Smart modems come with a media access controller inside which prevents random data from colliding and resending data that is not correctly received. Smart modems typically require more bandwidth than transparent modems, and typically use more radio frequency bandwidth. The IEEE [[802.11]] standard includes a short range modem that is used on a large scale throughout the world.

[[Image:fax modem antigo.jpg|thumb|[[USRobotics]] Sportster 14,400 Fax Modem (1994)|alt=]]

In the early 1990s, V.32 modems operating at 9,600 bit/s were introduced, but were expensive and were only starting to enter the market when V.32bis was standardized, which operated at 14,400 bit/s.

Wireless Data Modems are used in [[WiFi]] or [[WiMax]] Standards.

[[Rockwell International]]'s chip division developed a new driver chip set incorporating the [[V.32bis]] standard and aggressively priced it. [[Supra, Inc.]] arranged a short-term exclusivity arrangement with Rockwell, and developed the [[SupraFAXModem 14400]] based on it. Introduced in January 1992 at {{US$|long=no|399}} (or less), it was half the price of the slower V.32 modems already on the market. This led to a price war, and by the end of the year V.32 was dead, never having been really established, and V.32bis modems were widely available for {{US$|long=no|250}}.

[[WiFi]]= could be used in laptops for internet connections ([[wireless access point]] and [[wireless application protocol/WAP]])

V.32bis was so successful that the older high-speed standards had little advantages. USRobotics (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'', but neither non-standard modem sold well.

[[File:ModemISAv34.jpg|thumb|left|upright|V.34 modem implemented as an internal [[Industry Standard Architecture|ISA]] card]]

[[File:IBM PCMCIA Data-Fax Modem V.34 FRU 42H4326-8920.jpg|thumb|upright|V.34 data/fax modem as [[PC card]] for [[Notebook computer|notebooks]]]]

{{multiple image

| align = right

| image1 = Dr. Neuhaus, Smarty 28.8 TI-8923.jpg

| width1 = 150

| image2 = Dr. Neuhaus, Smarty 28.8 TI-8924.jpg

| width2 = 150

| footer = External V.34 modem with [[RS-232]] [[serial port]]

}}

Consumer interest in these proprietary improvements waned during the lengthy introduction of the {{val|28800|u=bit/s|fmt=commas}} [[ITU-T V.34|V.34]] standard. While waiting, several companies decided to release hardware and introduced modems they referred to as [[V.Fast]].

In order to guarantee compatibility with V.34 modems once a standard was ratified (1994), manufacturers used more flexible components, generally a [[digital signal processor|DSP]] and [[microcontroller]], as opposed to purpose-designed [[Application-specific integrated circuit|ASIC]] modem chips. This would allow later firmware updates to conform with the standards once ratified.

The ITU standard V.34 represents the culmination of these joint efforts. It employed the most powerful coding techniques available at the time, including channel encoding and shape encoding. From the mere four bits per symbol ({{val|9.6|ul=kbit/s}}), the new standards used the functional equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2,400 to 3,429, to create 14.4, 28.8, and {{val|33.6|u=kbit/s}} modems. This rate is near the theoretical [[Shannon limit]] of a phone line.<ref>{{cite book|last=Held|first=Gilbert|title=Understanding Data Communications: From Fundamentals to Networking Third Edition|year=2000|publisher=John Wiley & Sons Ltd|___location=New York|pages=68–69}}</ref>

===== {{anchor|56k}} {{val|56|u=kbit/s}} technologies =====

While {{val|56|u=kbit/s}} speeds had been available for leased-line modems for some time, they did not become available for dial up modems until the late 1990s.

[[File:Modem-bank-1.jpg|thumb|right|100px|Dial-up modem bank at an ISP]]

In the late 1990s, technologies to achieve speeds above {{val|33.6|u=kbit/s}} began to be introduced. Several approaches were used, but all of them began as solutions to a single fundamental problem with phone lines.

By the time technology companies began to investigate speeds above {{val|33.6|u=kbit/s}}, telephone companies had switched almost entirely to all-digital networks. As soon as a phone line reached a local central office, a ''line card'' converted the analog signal from the subscriber to a digital one and conversely. While digitally encoded telephone lines notionally provide the same bandwidth as the analog systems they replaced, the digitization itself placed constraints on the ''types'' of waveforms that could be reliably encoded.

The first problem was that the process of analog-to-digital conversion is intrinsically lossy, but second, and more importantly, the digital signals used by the telcos were not "linear": they did not encode all frequencies the same way, instead utilizing a nonlinear encoding ([[Μ-law algorithm|μ-law]] and [[A-law algorithm|a-law]]) meant to favor the nonlinear response of the human ear to voice signals. This made it very difficult to find a {{val|56|u=kbit/s}} encoding that could survive the digitizing process.

Modem manufacturers discovered that, while the analog to digital conversion could not preserve higher speeds, ''digital-to-analog'' conversions could. Because it was possible for an ISP to obtain a direct digital connection to a telco, a ''digital modem''{{snd}} one that connects directly to a digital telephone network interface, such as T1 or PRI{{snd}} could send a signal that utilized every bit of bandwidth available in the system. While that signal still had to be converted back to analog at the subscriber end, that conversion would not distort the signal in the same way that the opposite direction did.

====== {{Anchor|X2|K56flex}} Early 56k dial-up products ======

The first 56k (56&nbsp;kbit/s) dial-up option was a proprietary design from [[USRobotics]], which they called "X2" because 56k was twice the speed (×2) of 28k modems.

At that time, USRobotics held a 40% share of the retail modem market, while Rockwell International held an 80% share of the modem [[chipset]] market. Concerned with being shut out, Rockwell began work on a rival 56k technology. They joined with [[Lucent]] and [[Motorola]] to develop what they called "K56Flex" or just "Flex".

Both technologies reached the market around February 1997; although problems with K56Flex modems were noted in product reviews through July, within six months the two technologies worked equally well, with variations dependent largely on local connection characteristics.<ref>{{Cite book |last=Ross, John A. |title=Telecommunication technologies: voice, data & fiber-optic applications |date=2001 |publisher=Prompt |isbn=0-7906-1225-9 |___location=Indianapolis, Ind. |pages=185 |oclc=45745196}}</ref>

The retail price of these early 56k modems was about {{US$|200}}, compared to {{US$|long=no|100}} for standard 33k modems. Compatible equipment was also required at the [[Internet service provider]]s (ISPs) end, with costs varying depending on whether their current equipment could be upgraded. About half of all ISPs offered 56k support by October 1997. Consumer sales were relatively low, which USRobotics and Rockwell attributed to conflicting standards.<ref name="GS2006">{{cite book |last1=Greenstein |first1=Shane |last2=Stango |first2=Victor |title=Standards and Public Policy |url=https://books.google.com/books?id=3hMKHwUmaZ8C&pg=PA129 |year=2006 |publisher=Cambridge University Press |isbn=978-1-139-46075-0 |pages=129–132 |url-status=live |archive-url=https://web.archive.org/web/20170324040643/https://books.google.com/books?id=3hMKHwUmaZ8C&pg=PA129 |archive-date=2017-03-24}}</ref>

====== Standardized 56k (V.90/V.92) ======

In February 1998, The [[International Telecommunication Union]] (ITU) announced the draft of a new {{val|56|u=kbit/s}} standard [[ITU-T V.90|V.90]] with strong industry support. Incompatible with either existing standard, it was an amalgam of both, but was designed to allow both types of modem by a firmware upgrade. The V.90 standard was approved in September 1998 and widely adopted by ISPs and consumers.<ref name="GS2006" /><ref>{{cite web |url=http://www.itu.int/newsarchive/press_releases/1998/04.html |title=Agreement reached on 56K Modem standard |date=9 February 1998 |website=International Telecommunication Union |access-date=5 September 2018 |archive-url=https://web.archive.org/web/20171002194141/http://www.itu.int/newsarchive/press_releases/1998/04.html |archive-date=2 October 2017 |url-status=live}}</ref>

The [[ITU-T V.92]] standard was approved by ITU in November 2000<ref>{{Cite web |title=V.92: Enhancements to Recommendation V.90 |url=https://www.itu.int/rec/T-REC-V.92-200011-I/en |access-date=2020-06-29 |website=www.itu.int}}</ref> and utilized digital [[Pulse-code modulation|PCM]] technology to increase the upload speed to a maximum of {{val|48|u=kbit/s}}.

The high upload speed was a tradeoff. Use of the {{val|48|u=kbit/s}} upstream rate would reduce the downstream as low as {{val|40|u=kbit/s}} due to echo effects on the line. To avoid this problem, V.92 modems offer the option to turn off the digital upstream and instead use a plain 33.{{val|6|u=kbit/s}} analog connection in order to maintain a high digital downstream of {{val|50|u=kbit/s}} or higher.<ref>{{cite web |url=http://www.modemsite.com/56k/v92s.asp |title=V.92 – News & Updates |access-date=17 September 2012 |work=November and October 2000 updates |url-status=live |archive-url=https://web.archive.org/web/20120920104645/http://modemsite.com/56k/v92s.asp |archive-date=20 September 2012}}</ref>

V.92 also added 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. The second feature is the ability to quickly connect to one's ISP, achieved by remembering the analog and digital characteristics of the telephone line and using this saved information when reconnecting.

=== Evolution of dial-up speeds ===

These values are maximum values, and actual values may be slower under certain conditions (for example, noisy phone lines).<ref>{{cite web |author=tsbmail |url=http://www.itu.int/rec/T-REC-V/en |title=Data communication over the telephone network |publisher=Itu.int |date=2011-04-15 |access-date=2014-02-10 |url-status=live |archive-url=https://web.archive.org/web/20140127142624/http://www.itu.int/rec/T-REC-V/en |archive-date=2014-01-27 }}</ref> For a complete list see the companion article ''[[list of device bandwidths]]''. A [[baud]] is one symbol per second; each symbol may encode one or more data bits.

{| class="wikitable sortable"

|-

! style="text-align:left;"| Connection !! [[Modulation]] !! [[Bit rate]] [kbit/s] !! Year released

|-

| 110 [[baud]] [[Bell 101]] modem || FSK || 0.1 || 1958

|-

| 300 baud ([[Bell 103]] or [[ITU-T V.21|V.21]]) || FSK || 0.3 || 1962

|-

| 1,200 bit/s (1200 baud) ([[Bell 202]]) || FSK || 1.2 || 1976

|-

| 1,200 bit/s (600 baud) ([[Bell 212A]] or [[ITU-T V.22|V.22]]) || QPSK || 1.2 || 1980<ref name=tldp-mod>{{cite web |url=http://tldp.org/HOWTO/Modem-HOWTO-29.html |title=29.2 Historical Modem Protocols |publisher=tldp.org |access-date=2014-02-10 |url-status=live |archive-url=https://web.archive.org/web/20140102211723/http://tldp.org/HOWTO/Modem-HOWTO-29.html |archive-date=2014-01-02 }}</ref><ref>{{cite web|url=http://users.encs.concordia.ca/~youssef/comp445/ch3.pdf |archive-url=https://web.archive.org/web/20061007063755/http://users.encs.concordia.ca/~youssef/comp445/ch3.pdf |url-status=dead |archive-date=2006-10-07 |title=concordia.ca&nbsp;– Data Communication and Computer Networks |access-date=2014-02-10}}</ref>

|-

| 2,000 bit/s (1000 baud) (Bell 201A) || PSK || 2.0 || 1962

|-

| 2,400 bit/s (600 baud) ([[ITU-T V.22bis|V.22bis]]) || QAM || 2.4 || 1984<ref name=tldp-mod/>

|-

| 2,400 bit/s (1200 baud) ([[ITU-T V.26bis|V.26bis]]) || PSK || 2.4 ||

|-

| 4,800 bit/s (1600 baud) ([[ITU-T V.27ter|V.27ter]]) || PSK || 4.8 || 1976<!--Phase=PSK?--><ref>{{cite web |url=http://www.garretwilson.com/essays/computers/group3fax.html |title=Group 3 Facsimile Communication |publisher=garretwilson.com |date=2013-09-20 |access-date=2014-02-10 |url-status=live |archive-url=https://web.archive.org/web/20140203210353/http://www.garretwilson.com/essays/computers/group3fax.html |archive-date=2014-02-03 }}</ref><ref>{{cite book|title=INTERNATIONAL TELECOMMUNICATION UNION - CCITT - VOLUME VIII - FASCICLE Vlll/I - DATA COMMUNICATION OVER THE TELEPHONE NETWORK - RECOMMENDATIONS OF THE V SERIES|url=https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.258.43.en.1025.pdf|section=Recommendation V.27 ter|section-url=https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.258.43.en.1025.pdf#page=157|series=YELLOW BOOK|pages=148–160|publisher=[[International Telecommunication Union]] - [[ITU-T|International Telegraph and Telephone Consultative Committee (CCITT)]]}}</ref>

|-

| 4,800 bit/s (1600 baud, Bell 208B) || DPSK || 4.8 ||

|-

| 9,600 bit/s (2400 baud) ([[ITU-T V.32|V.32]]) || [[Trellis coded modulation|trellis]] || 9.6 || 1984<ref name=tldp-mod/>

|-

| 14.4&nbsp;kbit/s (2400 baud) ([[ITU-T V.32|V.32bis]]) || trellis || 14.4 || 1991<ref name=tldp-mod/>

|-

| 19.2&nbsp;kbit/s (2400 baud) ([[V.32terbo]]) || trellis || 19.2 || 1993<ref name=tldp-mod/>

|-

| 28.8&nbsp;kbit/s (3200 baud) ([[ITU-T V.34|V.34]]) || trellis || 28.8 || 1994<ref name=tldp-mod/>

|-

| 33.6&nbsp;kbit/s (3429 baud) ([[ITU-T V.34|V.34]]) || trellis || 33.6 || 1996<ref>{{cite web|url=http://www.vlsi.ee.upatras.gr/~mgalanis/pubs/v34_paper.pdf |archive-url=https://web.archive.org/web/20070306230217/http://www.vlsi.ee.upatras.gr/~mgalanis/pubs/v34_paper.pdf |url-status=dead |archive-date=2007-03-06 |title=upatras.gr – Implementation of a V.34 modem on a Digital Signal Processor |access-date=2014-02-10}}</ref>

|-

| 56&nbsp;kbit/s (8000/3429 baud) ([[ITU-T V.90|V.90]]) || digital || 56.0/33.6 || 1998<ref name=tldp-mod/>

|-

| 56&nbsp;kbit/s (8000/8000 baud) ([[ITU-T V.92|V.92]]) || digital || 56.0/48.0 || 2000<ref name=tldp-mod/>

|-

| Bonding modem (two 56k modems) ([[ITU-T V.92|V.92]])<ref>{{cite web|url=http://www.56k.com/reports/bonding.shtml|archive-url=https://web.archive.org/web/19971210202848/http://www.56k.com/reports/bonding.shtml|url-status=dead|archive-date=1997-12-10|title=Bonding: 112K, 168K, and beyond|last=Jones|first=Les|publisher=56K.COM}}</ref> || || 112.0/96.0 ||

|-

| Hardware compression (variable) ([[ITU-T V.90|V.90]]/[[ITU-T V.42bis|V.42bis]]) || || 56.0–220.0 ||

|-

| Hardware compression (variable) ([[ITU-T V.92|V.92]]/[[ITU-T V.44|V.44]]) || || 56.0–320.0 ||

|-

| Server-side web compression (variable) ([[Netscape#Netscape Internet Service|Netscape ISP]]) || || 100.0–1,000.0 ||

|}

=== Compression ===

Many dial-up modems implement standards for [[data compression]] to achieve higher effective throughput for the same bitrate. [[ITU-T V.44|V.44]]<ref>{{Cite web |title=V.44 |url=http://www.linfo.org/v_44.html |access-date=2023-04-06 |website=www.linfo.org}}</ref> is an example used in conjunction with [[ITU-T V.92|V.92]] to achieve speeds greater than 56k over ordinary phone lines.<ref>{{Cite web |title=V.92 |url=https://www.techopedia.com/definition/3018/v-92 |access-date=2023-04-06 |website=Techopedia |language=en-US}}</ref>

As telephone-based 56k modems began losing popularity, some Internet service providers such as [[NetZero|Netzero]]/Juno, [[Netscape]], and others started using pre-compression to increase apparent throughput. This server-side compression can operate much more efficiently than the on-the-fly compression performed within modems, because the compression techniques are content-specific (JPEG, text, EXE, etc.).The drawback is a loss in quality, as they use [[lossy compression]] which causes images to become pixelated and smeared. ISPs employing this approach often advertised it as "accelerated dial-up".<ref>{{Cite web |date=2004-06-15 |title=How High-speed Dial-up Works |url=https://computer.howstuffworks.com/high-speed.htm |access-date=2023-04-06 |website=HowStuffWorks |language=en-us}}</ref>

These accelerated downloads are integrated into the [[Opera (web browser)|Opera]]<ref>{{Cite web |last=Holcombe |first=Jeremy |date=2019-05-01 |title=How To Enable Turbo Mode in Opera |url=https://www.greengeeks.com/tutorials/how-to-enable-turbo-mode-in-opera/ |access-date=2023-04-06 |website=GreenGeeks |language=en-US}}</ref> and [[Amazon Silk]]<ref name=":1">{{Cite web |last=Shimpi |first=Anand Lal |title=Amazon's Silk Browser Acceleration Tested: Less Bandwidth Consumed, But Slower Performance |url=https://www.anandtech.com/show/5139/amazons-silk-browser-tested-less-bandwidth-consumed-but-slower-performance |archive-url=https://web.archive.org/web/20111123174049/http://www.anandtech.com/show/5139/amazons-silk-browser-tested-less-bandwidth-consumed-but-slower-performance |url-status=dead |archive-date=November 23, 2011 |access-date=2023-04-06 |website=www.anandtech.com}}</ref> web browsers, using their own server-side text and image compression requiring all data to pass through their own servers before reaching the user.<ref name=":1" />

=== Methods of attachment ===

Dial-up modems can attach in two different ways: with an acoustic coupler, or with a direct electrical connection.

==== Directly connected modems ====

The case ''[[Hush-A-Phone Corp. v. United States]]'', which legalized acoustic couplers, applied only to mechanical connections to a telephone set, not electrical connections to the telephone line. The ''[[Carterfone]]'' decision of 1968, however, permitted customers to attach devices directly to a telephone line as long as they followed stringent Bell-defined standards for non-interference with the phone network.<ref name=":0" /> This opened the door to independent (non-AT&T) manufacture of direct-connect modems, that plugged directly into the phone line rather than via an acoustic coupler.

While ''Carterfone'' required AT&T to permit connection of devices, AT&T successfully argued that they should be allowed to require the use of a special device to protect their network, placed in between the third-party modem and the line, called a [[Data access arrangement|Data Access Arrangement]] (DAA). The use of DAAs was mandatory from 1969 to 1975 when the new FCC Part 68 rules allowed the use of devices without a Bell-provided DAA, subject to equivalent circuitry being included in the third-party device.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=2otFgtEgfiEC&q=FCC%20%22automatic%20DAA%22&pg=PA1|title=Computerworld|date=1975-11-12|publisher=IDG Enterprise|language=en}}</ref>

Virtually all modems produced after the 1980s are direct-connect.

==== Acoustic couplers ====

{{See also|Acoustic coupler||category=no}}[[Image:Acoustic coupler 20041015 175456 1.jpg|thumb|The ''Novation CAT'' acoustically coupled modem]]

While Bell (AT&T) provided modems that attached via direct wire connection to the phone network as early as 1958, their regulations at the time did not permit the direct electrical connection of any non-Bell device to a telephone line. However, the [[Hush-A-Phone Corp. v. United States|Hush-a-Phone ruling]] allowed customers to attach any device ''to a telephone set'' as long as it did not interfere with its functionality. This allowed third-party (non-Bell) manufacturers to sell modems utilizing an ''acoustic coupler''.<ref name=":0">{{Cite web|title=The History of the Modem|url=https://www.techopedia.com/2/25804/networking/history-of-the-modem|access-date=2020-08-13|website=Techopedia.com|language=en}}</ref>

With an acoustic coupler, an ordinary telephone handset was placed in a cradle containing a speaker and microphone positioned to match up with those on the handset. The tones used by the modem were transmitted and received into the handset, which then relayed them to the phone line.<ref>{{Cite web|title=The Modem {{!}} Invention & Technology Magazine|url=https://www.inventionandtech.com/content/modem-0|access-date=2020-08-13|website=www.inventionandtech.com}}</ref>

Because the modem was not electrically connected, it was incapable of picking up, hanging up or dialing, all of which required direct control of the line. Touch-tone dialing would have been possible, but touch-tone was not universally available at this time. Consequently, the dialing process was executed by the user lifting the handset, dialing, then placing the handset on the coupler. To accelerate this process, a user could purchase a ''dialer'' or ''Automatic Calling Unit''.

=== Automatic calling units ===

Early modems could not place or receive calls on their own, but required human intervention for these steps.

As early as 1964, Bell provided automatic calling units that connected separately to a second serial port on a host machine and could be commanded to open the line, dial a number, and even ensure the far end had successfully connected before transferring control to the modem.<ref>{{Cite web|date=1964-03-01|title=801A Automatic Calling Unit Interface Specification|url=http://bitsavers.org/communications/westernElectric/modems/801A_Automatic_Calling_Unit_Interface_Specification_Mar64.pdf}}</ref> Later on, third-party models would become available, sometimes known simply as ''dialers'', and features such as the ability to automatically sign in to time-sharing systems.<ref>{{Cite web|date=1970-02-18|title=Computerworld|url=https://archive.org/details/computerworld4125unse6|access-date=2020-08-13|website=Internet Archive|language=en}}</ref>

Eventually this capability would be built into modems and no longer require a separate device.

=== Controller-based modems vs. soft modems ===

{{Main|Softmodem}}[[Image:WinmodemAndRegularModem.jpg|thumb|right|A PCI Winmodem soft modem (on the left) next to a conventional ISA modem (on the right)]]

Prior to the 1990s, modems contained all the electronics and intelligence to convert data in discrete form to an analog (modulated) signal and back again, and to handle the dialing process, as a mix of discrete logic and special-purpose chips. This type of modem is sometimes referred to as ''controller-based''.<ref>{{Cite web|title=USRobotics 56K Modem Education: What are the different types of modems?|url=https://support.usr.com/education/modem2.asp|access-date=2020-08-11|website=support.usr.com}}</ref>

In 1993, Digicom introduced the ''Connection 96 Plus'', a modem which replaced the discrete and custom components with a general purpose digital signal processor, which could be reprogrammed to upgrade to newer standards.<ref>{{Cite web|title=PC Computing Magazine Volume 6 Issue 7 : Ziff-Davis Publishing : Free Download, Borrow, and Streaming|url=https://archive.org/details/pc-computing-magazine-v6i7|access-date=2020-08-14|website=Internet Archive|date=July 1993|language=en}}</ref>

Subsequently, USRobotics released the ''Sportster Winmodem'', a similarly upgradable DSP-based design.<ref>{{Cite web|title=InfoWorld : InfoWorld Media Group, Inc. : Free Download, Borrow, and Streaming|url=https://archive.org/details/bub_gb_tD0EAAAAMBAJ|access-date=2020-08-14|website=Internet Archive|date=17 June 1996|language=en}}</ref>

As this design trend spread, both terms – ''soft modem'' and ''Winmodem'' – obtained a negative connotation in non-Windows-based computing circles because the drivers were either unavailable for non-Windows platforms, or were only available as unmaintainable closed-source binaries, a particular problem for Linux users.<ref>{{Cite web|title=Modem-HOWTO – Modems for a Linux PC • tldp.Docs.sk|url=http://tldp.docs.sk/howto/modem/Modem-HOWTO-2.html|access-date=2020-08-14|website=tldp.docs.sk}}</ref>

Later in the 1990s, software-based modems became available. These are essentially sound cards, and in fact a common design uses the [[AC'97]] audio codec, which provides multichannel audio to a PC and includes three audio channels for modem signals.

The audio sent and received on the line by a modem of this type is generated and processed entirely in software, often in a device driver. There is little functional difference from the user's perspective, but this design reduces the cost of a modem by moving most of the processing power into inexpensive software instead of expensive hardware [[Digital signal processor|DSPs]] or discrete components.

Soft modems of both types either are internal cards or connect over external buses such as [[USB]]. They never utilize RS-232 because they require high bandwidth channels to the host computers to carry the raw audio signals generated (sent) or analyzed (received) by software.

Since the interface is not RS-232, there is no standard for communication with the device directly. Instead, soft modems come with drivers which create an emulated RS-232 port, which standard modem software (such as an operating system dialer application) can communicate with.

=== Voice/fax modems ===

"Voice" and "fax" are terms added to describe any dial modem that is capable of recording/playing audio or transmitting/receiving faxes. Some modems are capable of all three functions.<ref>{{Cite web|last=ID|first=FCC|title=E110 56K Data/Fax Voice Soeakphone External Modem User Manual PTT Turbocomm Tech .|url=https://fccid.io/N7ZE110/User-Manual/USERS-MANUAL-20838|access-date=2020-08-13|website=FCC ID|language=en}}</ref>

[[Voice modem command set|Voice modems]] are used for [[computer telephony integration]] applications as simple as placing/receiving calls directly through a computer with a headset, and as complex as fully automated [[robocall]]ing systems.

Fax modems can be used for computer-based faxing, in which faxes are sent and received without inbound or outbound faxes ever needing to ever be printed on paper. This differs from [[Internet fax|efax]], in which faxing occurs over the internet, in some cases involving no phone lines whatsoever.

=== Modem Over IP (Modem Relay) ===

The ITU-T V.150.1 Recommendation defines procedures for the inter-operation of PSTN to IP gateways.<ref>{{Cite web|title=ITU-T Recommendation database|url=https://www.itu.int/itu-t/recommendations/rec.aspx?rec=V.150|access-date=2021-12-30|website=ITU|language=en}}</ref> In a classic example of this setup, each dial-up modem would connect to a modem relay gateway. The gateways are then connected to an IP network (such as the Internet). The analog connection from the modem is terminated at the gateway and the signal is demodulated. The demodulated control signals are transported over the IP network in an [[Real-time Transport Protocol|RTP]] packet type defined as [[State Signaling Events]] (SSEs). The data from the demodulated signal is sent over the IP network via a transport protocol (also defined as an RTP payload) called [[Simple Packet Relay Transport]] (SPRT). Both the SSE and SPRT packet formats are defined in the V.150.1 Recommendation (Annex C and Annex B respectively). The gateway at the remote end that receives the packets uses the information to re-modulate the signal for the modem connected at that end.

While the V.150.1 Recommendation is not widely deployed, a pared down version of the recommendation called "Minimum Essential Requirements (MER) for V.150.1 Gateways" (SCIP-216) is used in [[Secure telephone|Secure Telephony]] applications.<ref>{{Cite web|title=Iicwg Scip 216|url=https://nisp.nw3.dk/standard/iicwg-scip-216.html|access-date=2021-12-30|website=nisp.nw3.dk}}</ref>

=== Cloud-based Modems ===

While traditionally a hardware device, fully software-based modems with the ability to be deployed in a cloud environment (such as [[Microsoft Azure]] or [[Amazon Web Services|AWS]]) do exist.<ref>{{Cite web|title=SIP Software Modem - Modem without an analog line|url=https://www.vocal.com/voip/sip-software-modem/|access-date=2021-12-30|website=www.vocal.com}}</ref> Leveraging a [[Voice over IP|Voice-over-IP]] (VoIP) connection through a [[SIP trunking|SIP Trunk]], the modulated audio samples are generated and sent over an IP network via [[Real-time Transport Protocol|RTP]] and an uncompressed audio codec (such as [[G.711]] μ-law or a-law).

=== Popularity ===

A 1994 [[Software Publishers Association]] found that although 60% of computers in US households had a modem, only 7% of households went online.<ref name="cgw199405">{{Cite magazine|date=May 1994|title=Software Publishing Association Unveils New Data|department=Read.Me|url=http://www.cgwmuseum.org/galleries/index.php?year=1994&pub=2&id=118|magazine=Computer Gaming World|pages=12|url-status=dead|archive-url=https://web.archive.org/web/20140703000430/http://www.cgwmuseum.org/galleries/index.php?year=1994&pub=2&id=118|archive-date=2014-07-03|access-date=2017-11-11}}</ref> A [[Consumer Electronics Association|CEA]] study in 2006 found that dial-up Internet access was declining in the US. In 2000, dial-up Internet connections accounted for 74% of all US residential Internet connections.{{citation needed|date=May 2013}} The United States demographic pattern for dial-up modem users per capita has been more or less mirrored in Canada and Australia for the past 20 years.

Dial-up modem use in the US had dropped to 60% by 2003, and stood at 36% in 2006.{{citation needed|date=May 2013}} Voiceband modems were once the most popular means of [[Internet]] access in the US, but with the advent of new ways of accessing the Internet, the traditional 56K modem was losing popularity. The dial-up modem is still widely used by customers in rural areas where DSL, cable, wireless broadband, satellite, or fiber optic service are either not available or they are unwilling to pay what the available broadband companies charge.<ref>{{cite web|author=Suzanne Choney |url=http://www.nbcnews.com/technology/technolog/aol-still-has-3-5-million-dial-subscribers-119355 |archive-url=https://web.archive.org/web/20130101194954/http://www.nbcnews.com/technology/technolog/aol-still-has-3-5-million-dial-subscribers-119355 |url-status=dead |archive-date=2013-01-01 |title=AOL still has 3.5 million dial-up subscribers – Technology on NBCNews.com |website=[[NBC News]] |access-date=2014-02-10}}</ref> In its 2012 annual report, [[AOL]] showed it still collected around $700 million in fees from about three million dial-up users.

=== TTY/TDD ===

[[Telecommunications device for the deaf|TDD]] devices are a subset of the [[teleprinter]] intended for use by the deaf or hard of hearing, essentially a small teletype with a built-in dial-up modem and acoustic coupler. The first models produced in 1964 utilized [[Frequency-shift keying|FSK]] modulation much like early computer modems.

== Leased-line modems ==

A [[leased line]] modem also uses ordinary phone wiring, like dial-up and DSL, but does not use the same network topology. While dial-up uses a normal phone line and connects through the telephone switching system, and DSL uses a normal phone line but connects to equipment at the telco central office, leased lines do not terminate at the telco.

Leased lines are pairs of telephone wire that have been connected together at one or more telco central offices so that they form a continuous circuit between two subscriber locations, such as a business' headquarters and a satellite office. They provide no power or dialtone - they are simply a pair of wires connected at two distant locations.

A dialup modem will not function across this type of line, because it does not provide the power, dialtone and switching that those modems require. However, a modem with leased-line capability can operate over such a line, and in fact can have greater performance because the line is not passing through the telco switching equipment, the signal is not filtered, and therefore greater bandwidth is available.

Leased-line modems can operate in 2-wire or 4-wire mode. The former uses a single pair of wires and can only transmit in one direction at a time, while the latter uses two pairs of wires and can transmit in both directions simultaneously. When two pairs are available, bandwidth can be as high as 1.5&nbsp;Mbit/s, a full data [[T1 line|T1]] circuit.<ref>{{Cite web|title=MODEMS lease line modem|url=https://www.data-connect.com/leased_line_modems_tech.htm|access-date=2020-08-11|website=www.data-connect.com}}</ref>

While the slower leased line modems used, e.g., [[RS-232]], interfaces, the faster wideband modems used, e.g., [[List of ITU-T V-series recommendations#Wideband modems|V.35]].

==Broadband==

[[Image:T-DSL_ModemDSL Modem.jpg|thumb|250pxleft|[[DSL Modemmodem]]]]

[[File:ARRIS CM820B DOCSIS Cable Modem.jpg|thumb|Cable modem]]

[[Asymmetric Digital Subscriber Line|ADSL]] modems, a more recent development, are not limited to the telephone's "voiceband" audio frequencies. Some ADSL modems use [[coded orthogonal frequency division modulation]].

The term ''[[broadband]]'' was previously<ref>{{cite book

[[Cable modem]]s use a range of frequencies originally intended to carry RF television channels. 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 multiplexing]].

| title = Engineering and Operations in the Bell System

| id = 500-478

| edition = Second

| year = 1984

| editor = R. F. Rey

| isbn = 0-932764-04-5

| lccn = 83-72956

| page = [http://bitsavers.org/communications/westernElectric/books/Engineering_and_Operations_in_the_Bell_System_2ed_1984.pdf#page=62 45]

| section = 2.2.3 Data Products

| section-url = http://bitsavers.org/communications/westernElectric/books/Engineering_and_Operations_in_the_Bell_System_2ed_1984.pdf#page=60

| quote = Speeds on broadband private-line channels range from 19.2 to 230.4&nbsp;kbps.

| url = http://bitsavers.org/communications/westernElectric/books/Engineering_and_Operations_in_the_Bell_System_2ed_1984.pdf

| publisher = AT&T Bell Laboratories

| access-date = April 1, 2022

}}

</ref><ref>{{cite book

| title = Engineering and Operations in the Bell System

| id = 500-478

| edition = Second

| year = 1984

| editor = R. F. Rey

| isbn = 0-932764-04-5

| lccn = 83-72956

| page = 199

| section = 6.2.1 Basic Concept

| section-url = http://bitsavers.org/communications/westernElectric/books/Engineering_and_Operations_in_the_Bell_System_2ed_1984.pdf#page=215

| quote = Analog channels can be further characterized by bandwidth: narrowband channels (for example, 100 Hz, 200 Hz); voiceband channels (4 kHz);4 broadband channels (for example, 48 kHz, 240 kHz).

| url = http://bitsavers.org/communications/westernElectric/books/Engineering_and_Operations_in_the_Bell_System_2ed_1984.pdf

| publisher = AT&T Bell Laboratories

| access-date = April 1, 2022

}}

</ref> used to describe communications faster than what was available on voice grade channels.

The term ''[[broadband]]'' gained widespread adoption in the late 1990s to describe internet access technology exceeding the 56 kilobit/s maximum of dialup. There are many broadband technologies, such as various DSL ([[digital subscriber line]]) technologies and cable broadband.

New types of broadband modems are beginning to appear, such as [[doubleway]] [[satellite]] and [[Electric_power_transmission|powerline]] modems.

DSL technologies such as [[Asymmetric digital subscriber line|ADSL]], [[High-bit-rate digital subscriber line|HDSL]], and [[VDSL]] use telephone lines (wires that were installed by a telephone company and originally intended for use by a telephone subscriber) but do not utilize most of the rest of the telephone system. Their signals are not sent through ordinary phone exchanges, but are instead received by special equipment (a [[Digital subscriber line access multiplexer|DSLAM]]) at the telephone company central office.

Broadband modems should still be classed as modems, since they do utilise analog/digital conversion. They are more advanced devices that traditional telephone modems as they are capable of modulating/demodulating hundreds of channels simultaneously.

Because the signal does not pass through the telephone exchange, no "dialing" is required, and the bandwidth constraints of an ordinary voice call are not imposed. This allows much higher frequencies, and therefore much faster speeds. ADSL in particular is designed to permit voice calls and data usage over the same line simultaneously.

Many broadband "modems" include the functions of a router and other features such as DHCP, NAT and firewall features.

Similarly, [[cable modem]]s use infrastructure originally intended to carry television signals, and like DSL, typically permit receiving television signals at the same time as broadband internet service.

When broadband technology was introduced, networking and routers were not very familiar to most people. However, many people knew what a modem was as most internet access was through dialup. Due to this familiarity, companies started selling broadband adapters using the familiar term "modem".

Other broadband modems include [[FTTx]] modems, [[satellite modem]]s, and [[Power line communication|power line]] modems.

==Popularity==

Modems are the most popular means of [[Internet]] access. A [[UCLA]] 2001 study of American Internet users showed that 81.3% of them used a telephone modem and 11.5% used a cable modem though, with the advent of new ways of accessing the internet, the traditional 56K modem is fast losing popularity.

=== Terminology ===

{{Internet Access}}

Different terms are used for broadband modems, because they frequently contain more than just a modulation/demodulation component.

Because high-speed connections are frequently used by multiple computers at once, many broadband modems do not have direct (e.g. USB) PC connections. Rather they connect over a network such as Ethernet or Wi-Fi. Early broadband modems offered [[Ethernet]] handoff allowing the use of one or more public IP addresses, but no other services such as NAT and DHCP that would allow multiple computers to share one connection. This led to many consumers purchasing separate "broadband routers," placed between the modem and their network, to perform these functions.<ref>{{Cite web|title=What's the Difference between a Modem and Router?|url=https://www.lifewire.com/difference-between-modem-and-router-4159854|access-date=2021-11-23|website=Lifewire|language=en}}</ref><ref>{{Cite web|date=2021-04-07|title=Modem vs. router: The differences between the pieces of hardware that connect you to the internet, explained|url=https://www.businessinsider.com/guides/tech/modem-vs-router|access-date=2021-11-23|website=Business Insider Australia|language=en-AU}}</ref>

Eventually, ISPs began providing [[residential gateway]]s which combined the modem and broadband router into a single package that provided routing, [[Network address translation|NAT]], security features, and even [[Wi-Fi]] access in addition to modem functionality, so that subscribers could connect their entire household without purchasing any extra equipment. Even later, these devices were extended to provide "[[Triple play (telecommunications)|triple play]]" features such as telephony and television service. Nonetheless, these devices are still often referred to simply as "modems" by service providers and manufacturers.<ref>hp.com/us-en/shop/tech-takes/modem-vs-router</ref>

Consequently, the terms "modem", "router", and "gateway" are now used interchangeably in casual speech, but in a technical context "modem" may carry a specific connotation of basic functionality with no routing or other features, while the others describe a device with features such as NAT.<ref>{{Cite web|date=2021-02-11|title=Modem vs. Router: What's the Difference?|url=https://www.nytimes.com/wirecutter/blog/modem-vs-router/|access-date=2021-11-23|website=Wirecutter: Reviews for the Real World|language=en-US}}</ref><ref>{{Cite web|title=Modem vs Router: What's the Difference?|url=https://www.xfinity.com/hub/internet/modem-vs-router|access-date=2021-11-23|website=Xfinity|language=en}}</ref>

Broadband modems may also handle authentication such as [[Point-to-Point Protocol over Ethernet|PPPoE]]. While it is often possible to authenticate a broadband connection from a users PC, as was the case with dial-up internet service, moving this task to the broadband modem allows it to establish and maintain the connection itself, which makes sharing access between PCs easier since each one does not have to authenticate separately. Broadband modems typically remain authenticated to the ISP as long as they are powered on.

==Radio==

{{unreferenced section|date=October 2017}}

[[File:Espressif ESP-WROOM-32 Wi-Fi & Bluetooth Module.jpg|left|thumb|A bluetooth radio module with built-in antenna (left)]]

Any communication technology sending digital data wirelessly involves a modem. This includes [[direct broadcast satellite]], [[WiFi]], [[WiMAX|WiMax]], [[mobile phone]]s, [[Global Positioning System|GPS]], [[Bluetooth]] and [[Near-field communication|NFC]].

Modern telecommunications and data networks also make extensive use of [[radio modem]]s where long distance data links are required. Such systems are an important part of the [[PSTN]], and are also in common use for high-speed [[computer networking|computer network]] links to outlying areas where [[Fiber-optic communication|fiber optic]] is not economical.

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 wireless communication links to work simultaneously on different frequencies.{{Relevance inline||date=August 2020|reason=I don't recognize any of this terminology and from a little googling I suspect it is too low-level for this consumer-electronics-oriented article.}}

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. 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 media access controllers 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.

===Mobile broadband===

{{See also|Mobile broadband|Mobile broadband modem}}

[[File:Huawei E173 3G HSPA+ Modem USB Movistar Colombia (6).jpg|thumb|[[Huawei]] [[HSPA+]] ([[Evolution-Data Optimized|EVDO]]) USB wireless modem from [[Movistar]] Colombia|alt=|110x110px]]

[[File:Huawei 4G+ Modem.jpg|thumb|Huawei 4G+ Dual Band Modem|alt=|left|127x127px]]

Modems which use a mobile telephone system ([[GPRS]], [[UMTS]], [[High Speed Packet Access|HSPA]], [[Evolution-Data Optimized|EVDO]], [[WiMAX|WiMax]], [[5G]] etc.), are known as mobile broadband modems (sometimes also called wireless modems). Wireless modems can be embedded inside a [[laptop]], mobile phone or other device, or be connected externally. External wireless modems include [[connect card]]s, USB modems, and [[cellular router]]s.

Most [[GSM]] wireless modems come with an integrated [[SIM card]]holder (i.e. [[Huawei E220]], Sierra 881.) Some models are also provided with a microSD memory slot and/or jack for additional external antenna, (Huawei E1762, Sierra Compass 885.)<ref>{{cite web |url=http://www.3gmodem.com.hk/Huawei/E1762.html |title=HUAWEI E1762, HSPA/UMTS 900/2100 Support 2Mbps (5.76Mbps ready) HSUPA and 7.2Mbps HSDPA services |publisher=3gmodem.com.hk |access-date=2013-04-22 |url-status=live |archive-url=https://web.archive.org/web/20130510031830/http://www.3gmodem.com.hk/Huawei/E1762.html |archive-date=2013-05-10 }}</ref><ref>{{cite web |url=http://www.reghardware.com/2008/07/16/review_sierra_compass_885/ |title=Sierra Wireless Compass 885 HSUPA 3G modem |publisher=The Register |access-date=2014-02-10 |url-status=live |archive-url=https://web.archive.org/web/20130104002944/http://www.reghardware.com/2008/07/16/review_sierra_compass_885/ |archive-date=2013-01-04 }}</ref>

The CDMA (EVDO) versions do not typically use [[Removable User Identity Module|R-UIM]] cards, but use [[Electronic Serial Number]] (ESN) instead.

Until the end of April 2011, worldwide shipments of USB modems surpassed embedded 3G and 4G modules by 3:1 because USB modems can be easily discarded. Embedded modems may overtake separate modems as tablet sales grow and the incremental cost of the modems shrinks, so by 2016, the ratio may change to 1:1.<ref>{{cite web

|url = http://www.pcworld.com/article/226887/article.html

|title = Laptop Users Still Prefer USB Modems

|last1 = Lawson

|first1 = Stephen

|date = May 2, 2011

|website = PCWorld

|publisher = IDG Consumer & SMB

|access-date = 2016-08-13

|url-status = live

|archive-url = https://web.archive.org/web/20160927225258/http://www.pcworld.com/article/226887/article.html

|archive-date = September 27, 2016

}}</ref>

Like mobile phones, mobile broadband modems can be SIM locked to a particular network provider. Unlocking a modem is achieved the same way as unlocking a phone, by using an [[Subsidy Password|'unlock code']].{{citation needed|date=July 2020}}

==Optical modem==

[[File:Tellabs ONT611 inside.jpeg|left|thumb|An ONT providing data, telephone and television service]]

A device that connects to a fiber optic network is known as an [[Network interface device#Optical network terminals|optical network terminal]] (ONT) or optical network unit (ONU). These are commonly used in [[Fiber-to-the home|fiber to the home]] installations, installed inside or outside a house to convert the optical medium to a copper Ethernet interface, after which a router or gateway is often installed to perform authentication, routing, NAT, and other typical consumer internet functions, in addition to "[[Triple play (telecommunications)|triple play]]" features such as telephony and television service. They are not a modem,{{disputed inline|date=April 2024}} although they perform a similar function and are sometimes referred to as a modem.

Fiber optic systems can use quadrature amplitude modulation to maximize throughput. 16QAM uses a 16-point constellation to send four bits per symbol, with speeds on the order of 200 or 400 gigabits per second.<ref>{{cite web

|title = Researchers double throughput of long-distance fiber optics

|url = http://www.techrepublic.com/article/researchers-double-throughput-of-long-distance-fiber-optics/

|date = February 10, 2015

|author1 = Michael Kassner

|website = TechRepublic

|url-status = live

|archive-url = https://web.archive.org/web/20161109152227/http://www.techrepublic.com/article/researchers-double-throughput-of-long-distance-fiber-optics/

|archive-date = November 9, 2016

}}</ref><ref>{{cite journal

|title = 112&nbsp;Gbit/s RF-assisted dual carrier DP-16-QAM transmitter using optical phase modulator

|journal = Optics Express

|volume = 19

|issue = 26

|pages = B784-9

|publisher = Optical Society of America

|author1 = Bengt-Erik Olsson

|author2 = Anders Djupsjöbacka

|author3 = Jonas Mårtensson

|author4 = Arne Alping

|date = 6 Dec 2011

|doi=10.1364/oe.19.00b784

|pmid = 22274103

|bibcode = 2011OExpr..19B.784O

|s2cid = 32757398

|doi-access= free

}}</ref> 64QAM uses a 64-point constellation to send six bits per symbol, with speeds up to 65 terabits per second. Although this technology has been announced, it may not yet be commonly used.<ref>{{cite web|author=Stephen Hardy|date=March 17, 2016|title=ClariPhy targets 400G with new 16-nm DSP silicon|url=http://www.lightwaveonline.com/articles/2016/03/clariphy-targets-400g-with-new-16-nm-dsp-silicon.html|url-status=live|archive-url=https://web.archive.org/web/20161109085339/http://www.lightwaveonline.com/articles/2016/03/clariphy-targets-400g-with-new-16-nm-dsp-silicon.html|archive-date=November 9, 2016|publisher=LIGHTWAVE}}</ref><ref>{{cite web|date=17 Mar 2016|title=ClariPhy Shatters Fiber and System Capacity Barriers with Industry's First 16nm Coherent Optical Networking Platform|url=http://optics.org/press/3152|website=optics.org}}</ref><ref>{{cite web

| url=http://company.nokia.com/en/news/press-releases/2016/10/12/alcatel-lucent-submarine-networks-and-nokia-bell-labs-achieve-65-terabit-per-second-transmission-record-for-transoceanic-cable-systems

| title=Nokia Bell Labs achieve 65 Terabit-per-second transmission record for transoceanic cable systems

| date=12 October 2016

| publisher=Noika

| access-date=8 November 2016

| archive-url=https://web.archive.org/web/20161109090213/http://company.nokia.com/en/news/press-releases/2016/10/12/alcatel-lucent-submarine-networks-and-nokia-bell-labs-achieve-65-terabit-per-second-transmission-record-for-transoceanic-cable-systems

| archive-date=9 November 2016

| url-status=dead

}}</ref>

==Home networking==

{{unreferenced section|date=October 2017}}

Although the name ''modem'' is seldom used, some high-speed home networking applications do use modems, such as [[Powerline Ethernet|powerline ethernet]]. The [[G.hn]] standard for instance, developed by [[ITU-T]], provides a high-speed (up to 1&nbsp;Gbit/s) [[local area network]] using existing home wiring (power lines, phone lines, and [[ethernet over coax|coaxial cables]]). G.hn devices use [[orthogonal frequency-division multiplexing]] (OFDM) to modulate a digital signal for transmission over the wire.

As described above, technologies like Wi-Fi and Bluetooth also use modems to communicate over radio at short distances.

== Null modem ==

[[File:Null modem.jpg|thumb|115x115px|Null modem adapter]]

A [[null modem]] cable is a specially wired cable connected between the [[serial port]]s of two devices, with the transmit and receive lines reversed. It is used to connect two devices directly without a modem. The same software or hardware typically used with modems (such as Procomm or Minicom) could be used with this type of connection.

A null modem adapter is a small device with plugs at both ends which is placed on the termination of a normal "straight-through" serial cable to convert it into a null-modem cable.

== Short-haul modem ==

A "short haul modem" is a device that bridges the gap between leased-line and dial-up modems. Like a leased-line modem, they transmit over "bare" lines with no power or telco switching equipment, but are not intended for the same distances that leased lines can achieve. Ranges up to several miles are possible, but significantly, short-haul modems can be used for ''medium'' distances, greater than the maximum length of a basic serial cable but still relatively short, such as within a single building or campus. This allows a serial connection to be extended for perhaps only several hundred to several thousand feet, a case where obtaining an entire telephone or leased line would be overkill.

While some short-haul modems do in fact use modulation, low-end devices (for reasons of cost or power consumption) are simple "line drivers" that increase the level of the digital signal but do not modulate it. These are not technically modems, but the same terminology is used for them.<ref>{{Cite web|title=Modem|url=http://www.trine2.net.au/Modem-Tutorial(YES!)/modem.htm#Short_Haul|access-date=2020-08-13|website=www.trine2.net.au}}</ref>

==See also==

{{Columns-list|colwidth=31em|

*[[56k line]]

* [[56&nbsp;kbit/s line]]

*[[Digital to analog converter]]

* [[Handshake (computing)|Handshaking]]

*[[Flat rate]]

* [[K56flexRaytheon BBN]]

* [[Command and Data modes (modem)]]

*[[Modulation]] (for a fuller list of modulation techniques)

* [[Fax demodulator]]

*[[Internet protocol suite|TCP/IP]]

* [[List of interface bit rates]]

*[[v.34]]

* [[List of ITU-T V-series recommendations]]

*[[v.90]]

* [[v.92Modulation]]

* [[X2 (Chipset)RJ-11]]

* [[Time Independent Escape Sequence]]

*[[Broadband]]: [[satellite modem]], [[ADSL]], [[cablemodem]], [[Power line communication|PLC]].

* [[Wake-on-ring]]

*Chapter [[b:Serial_Programming:Modems_and_AT_Commands|Hayes-compatible Modems and AT Commands]] of the [[b:Programming:Serial Data Communications|Serial Data Communications Programming]] ''[[Wikibook]]''

}}

== Further reading ==

* {{cite web|title=Modems: Market Overview|url=https://bitsavers.trailing-edge.com/pdf/datapro/Datapro_Reports_on_PC_and_LAN_Communications_1992/Vol1_570.pdf|date=September 1990|publisher=[[McGraw Hill]]|website=[[Datapro Research]]|series=Datapro Reports on PC & LAN Communications}}

==References==

{{Reflist|33em}}

==External links==

{{Wikibooks|Transferring Data between Standard Dial-Up Modems |Modems=}}

*[http://www.pcnineoneone.com/howto/modem1.html Installing, testing, troubleshooting & tweaking modems]

{{Commons category|Modems}}

*[http://www.56k.com 56k]

* [[b:Serial Programming/Modems and AT Commands|Hayes-compatible Modems and AT Commands]] from the [[b:Serial Programming|Serial Data Communications Programming]] ''[[Wikibook]]''

*[http://www.v92.com v.92]

* [http://www.itu.int/rec/recommendation.asp?type=products&lang=e&parent=T-REC-V International Telecommunication Union ITU]: Data communication over the telephone network

*[http://www.agere.com/ Agere Systems]

* [http://www.3amsystems.com/wireline/hmo.htm Basic handshakes & modulations] – V.22, V.22bis, V.32 and V.34 handshakes

*[http://www.broadxent.com/ Broadxent]

* [http://www.techradar.com/news/internet/getting-connected-a-history-of-modems-657479 Getting connected: a history of modems] – techradar

*[http://www.cc.columbia.edu/acis/networks/protocols.html Columbia University - Protocols Explained]

* [https://www.bugswave.com/difference-between-modems-and-routers/ Difference between Modems and Routers] – Bugswave

*[http://www.conexant.com/ Conexant Systems]

* [http://bitsavers.org/communications/westernElectric/books/Telecommunications_Transmission_Engineering_Vol_2_Facilities_1ed_1977.pdf Telecommunications Transmission_Engineering Volume 2 Facilities] - AT&T

*[http://modems.rosenet.net/ Costmo Modem Site]

*[http://www.creativelabs.com/ Creative Labs]

*[http://www.digicomsystems.com/ Digicom Systems]

*[http://computer.howstuffworks.com/modem.htm How Stuff Works - Modems]

*[http://www.itu.int/rec/recommendation.asp?type=products&lang=e&parent=T-REC-V International Telecommunications Union ITU]

*[http://www.modemhelp.org ModemHelp.org]

*[http://www.modem-help.co.uk/ Modem-Help.co.uk]

*[http://www.modems.com Modems.com]

*[http://www.modemsite.com/ ModemSite.com]

{{Modem standards}}

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