
A software modem, commonly referred to as a softmodem, is a
modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...
with minimal hardware that uses
software
Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications.
The history of software is closely tied to the development of digital comput ...
running on the host computer, and the computer's resources (especially the
central processing unit
A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
,
random access memory
Random-access memory (RAM; ) is a form of electronic computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written ...
, and sometimes
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
Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
. By analogy, a linmodem is a softmodem that can run on
Linux
Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
.
Softmodems are sometimes used as an example of a
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 couplers) and their protocols used relatively simple modulation techniques such as
FSK or
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
An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
s (ICs) such as logical gates,
PLLs and
microcontroller
A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...
s. Later techniques used in modern
V.34,
V.90 and
V.92 protocols (such as a 1664-point
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
LSI 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
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.
Likewise, the term "Winmodem" originated by Prof. Parvaiz Akhtar in 1996 with hardware being developed by
USRobotics' ''Sportster Winmodem'', a similarly upgradable DSP-based design.
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.
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 kbit/s leased-line softmodem called AuDSL from 1999, and the Minimodem project which implements several FSK modem standards.
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
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
,
demodulation and other tasks.
Some, known as "host-based" modems, may still use some amount of the host's CPU power for some tasks.
Pure software modems perform all modem tasks on the host PC's
CPU, while the hardware provides only analog-digital conversion and connection to the telephone network.
Advantages and disadvantages
The original stated purpose of the
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
modems. Their minimal
hardware design reduces
manufacturing
Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the
secondary sector of the economy. The term may refer ...
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.
While DSP-based softmodems usually only require host attention during startup, pure software modems consume some
CPU cycles on the host, which can conceivably slow down
application software
Application software is any computer program that is intended for end-user use not operating, administering or programming the computer. An application (app, application program, software application) is any program that can be categorized as ...
on older computers. This was a major issue in the 1990s, when
CPUs were not nearly as powerful as today's typical hardware.
DSL softmodems
Although "softmodem" typically applies to
PSTN
The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists ...
modems, there are some software-based
DSL modems or even
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
Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois. It was founded by brothers Paul and Joseph Galvin in 1928 and had been named Motorola since 1947. Many of Motorola's products had been ...
's SoftDSL chipset.
The term
WinDSL has been coined to describe this kind of technology.
DSL softmodems generally require the same interfaces as PSTN softmodems, such as
USB
Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...
or
PCI.
See also
*
Baseband processor
*
Geoport
*
Software-defined radio (SDR)
*
Winprinter
References
{{Reflist, 2
External links
A review of the differences between software-based modems and hardware-based modemsModems and their chipsets lists
Modems