Editing Softmodem

{{Short description|Modem that uses software to minimize the need for hardware}}
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[[File:WinmodemAndRegularModem.jpg|thumb|A [[Conventional PCI|PCI]] softmodem (left) next to a conventional [[Industry Standard Architecture|ISA]] hardware modem (right)]]

A '''software modem''', commonly referred to as a '''softmodem''', is a [[modem]] with minimal hardware that uses [[software]] running on the host computer, and the computer's resources (especially the [[central processing unit]], [[random access memory]], and sometimes [[Sound card|audio processing]]), in place of the hardware in a conventional modem.

Softmodems are also sometimes called '''winmodems''' due to limited support for platforms other than [[Microsoft Windows|Windows]]. By analogy, a '''linmodem''' is a softmodem that can run on [[Linux]].<ref>{{cite web |last=Walbran |first=Sean |date=2001-02-24 | url=https://www.tldp.org/HOWTO/Linmodem-HOWTO.html | title=Linmodem-HOWTO |work=[[Linux Documentation Project]] | access-date=2020-06-22}}</ref><ref>{{cite web | url=http://www.linmodems.org/ | archive-url=https://web.archive.org/web/20050103085641/http://www.linmodems.org/ | title=Linux Winmodem Support | archive-date=2005-01-03 | url-status=live }}</ref>

Softmodems are sometimes used as an example of a [[Real-time computing#Hard|hard real-time]] system. The audio signals to be transmitted must be computed on a tight interval (on the order of every 5 or 10 milliseconds); they cannot be computed in advance, and they cannot be late or the receiving modem will lose synchronization.

== History ==
The first generations of hardware modems (including [[acoustic coupler]]s) and their protocols used relatively simple modulation techniques such as [[Frequency Shift Keying|FSK]] or [[Amplitude Shift Keying|ASK]] at low speeds. Under these conditions, modems could be built with the analog [[discrete component]] technology used during the late 70s and early 80s.

As more sophisticated transmission schemes were devised, the circuits grew in complexity substantially. New modulation required mixing analog and digital components, and eventually incorporating multiple [[integrated circuit]]s (ICs) such as logical gates, [[Phase-locked loop|PLL]]s and [[microcontroller]]s. Later techniques used in modern [[ITU-T V.34|V.34]], [[ITU-T V.90|V.90]] and [[ITU-T V.92|V.92]] protocols (such as a 1664-point [[Quadrature amplitude modulation|QAM]] constellation) are so complex that implementing them with discrete components or general purpose ICs became impractical.

Furthermore, improved compression and error correction schemes were introduced in the newest protocols, requiring extra processing power in the modem itself. This made the construction of a mainly analog/discrete component modem impossible. Finally, compatibility with older protocols using completely different modulation schemes would have required a modem made with discrete electronics to contain multiple complete implementations.

Initially the solution was to use [[Large-Scale Integration|LSI]] [[Application-specific integrated circuit|ASICs]] which shrank the various implementations into a small number of components, but since standards continued to change, there was a desire to create modems that could be upgraded.

In 1993, Digicom marketed the ''Connection 96 Plus'', a modem based around a [[Digital signal processor|DSP]] which was programmed by an application on startup. Because the program was replaceable, the modem could be upgraded as standards improved. Digicom branded this technology ''SoftModem'', perhaps originating the term.<ref name=":0" />

Likewise, the term "Winmodem" originated by Prof. Parvaiz Akhtar in 1996 with hardware being developed by [[USRobotics|USRobotics']] ''Sportster Winmodem'', a similarly upgradable DSP-based design.<ref>{{Cite magazine |title=U.S. Robotics modem users to get soft upgrade to 33.6Kbps |last=Lee |first=Yvonne L. |work=InfoWorld |publisher=InfoWorld Media Group, Inc. |date=1996-06-10 |page=58 |volume=18 |issue=24 |url=https://archive.org/details/bub_gb_tD0EAAAAMBAJ|access-date=2020-08-14 |via=Internet Archive }}</ref>

In 1996, two types of modem began to reach the market: ''host-based'' modems, which offloaded some work onto the host CPU, and ''software-only'' modems which transferred all work onto the host system's CPU.<ref name=":1" /> In 1997, the [[AC'97]] standard for computer audio would introduce channels for modem use, making software modem technology common in PCs.

Since then, some softmodems have been created as standalone software projects utilizing standard sound card interfaces, such as an experimental open-source 96&nbsp;kbit/s leased-line softmodem called AuDSL from 1999,<ref>{{cite web |title=AuDSL - a software leased line modem |url=https://www.araneus.fi/audsl/ |website=www.araneus.fi |quote=AuDSL is an experimental software modem for low-speed Internet connectivity over leased copper lines using PC sound cards as the line interface. The acronym AuDSL stands for Audio Digital Subscriber Line.}}</ref> and the Minimodem project which implements several FSK modem standards.<ref>{{cite web |title=minimodem - general-purpose software audio FSK modem |url=http://www.whence.com/minimodem/ |website=www.whence.com |quote=It acts a general-purpose software FSK modem, and includes support for various standard FSK protocols such as Bell103, Bell202, RTTY, TTY/TDD, NOAA SAME, and Caller-ID.}}</ref>

== Types ==
Softmodems can be separated into two classes: ''controllerless'' modems and ''pure software'' modems.

Controllerless modems utilize a DSP on the modem itself to perform [[modulation]], [[demodulation]] and other tasks.<ref name=":0">{{Cite magazine|work=[[PC/Computing]] |date=July 1993 |last=Sandlund |first=Chris |title=Digicom's Connection 96 Plus: Is It Really the Last Modem You'll Ever Need? |page=74 |volume=6 |number=7 |publisher=[[Ziff-Davis]] |url=https://archive.org/details/pc-computing-magazine-v6i7|access-date=2020-08-14 |via=Internet Archive }}</ref> Some, known as "host-based" modems, may still use some amount of the host's CPU power for some tasks.<ref name=":1">{{Cite magazine |last1=Levin |first1=Carol |last2=Rupley |first2=Sebastian |title=Modem Makeovers |volume=15 |number=20 |page=34 |url=https://books.google.com/books?id=yeegNRKq1h0C&q=host+based+modem&pg=PA34|work=[[PC Magazine]] |date=1996-11-19|publisher=[[Ziff Davis]] }}</ref>

Pure software modems perform all modem tasks on the host PC's [[Central processing unit|CPU]], while the hardware provides only analog-digital conversion and connection to the telephone network.<ref name=":1" />

== Advantages and disadvantages ==
The original stated purpose of the [[Digital signal processor|DSP]]-based softmodem was to provide for upgradeability, a concern in an era when modem standards were changing rapidly. Both DSP and pure software modems offer this feature.

Softmodems provide cost and efficiency advantages over traditional hardware [[Modem|modems]]. Their minimal [[hardware design]] reduces [[manufacturing]] costs and [[power consumption]].

A downside of either type of softmodem is that drivers must be provided, and the terms "softmodem" and "winmodem" have gained negative connotations, particularly within the open-source community, due to drivers for Linux often being omitted or provided only as unmaintainable binaries.<ref>{{Cite web |last=Lawyer |first=David S. |date=2007 |title=Modem-HOWTO |url=https://tldp.org/HOWTO/Modem-HOWTO-2.html |work=[[Linux Documentation Project]] |access-date=2020-08-14}}</ref>

While DSP-based softmodems usually only require host attention during startup, pure software modems consume some [[Central processing unit|CPU]] cycles on the host, which can conceivably slow down [[application software]] on older computers. This was a major issue in the 1990s, when [[Central processing unit|CPU]]s were not nearly as powerful as today's typical hardware.

== DSL softmodems ==
Although "softmodem" typically applies to [[PSTN]] modems, there are some software-based [[Digital subscriber line|DSL]] modems or even [[Router (computing)|routers]], which work on the same principles but at higher bandwidth and with more complex encoding schemes. One of the first software based DSL modem chipsets was [[Motorola]]'s SoftDSL chipset.<ref>{{Cite web |archive-url=https://web.archive.org/web/20070518032851/http://www.motorola.com/softmodem/softDSL.htm |archive-date=2007-05-18 |url-status=dead |title=SoftDSL Solutions |publisher=Motorola |url=http://www.motorola.com/softmodem/softDSL.htm}}</ref>

The term [[WinDSL]] has been coined to describe this kind of technology.<ref>{{cite web | url = https://tech.slashdot.org/story/00/04/20/091202/windsl-coming | title = WinDSL Coming? |work=[[Slashdot]] |date=2000-04-20 }}</ref> DSL softmodems generally require the same interfaces as PSTN softmodems, such as [[Universal Serial Bus|USB]] or [[Peripheral Component Interconnect|PCI]].

==See also==
* [[Baseband processor]]
* [[Geoport]]
* [[Software-defined radio]] (SDR)
* [[Winprinter]]

==References==
{{Reflist|2}}

== External links ==
* [http://www.56k.com/reports/winmodem.shtml A review of the differences between software-based modems and hardware-based modems]
* [http://www.xmodem.org/ Modems and their chipsets lists ]

[[Category:Modems]]