Modem
Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines.
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.
The 201A Data-Phone was a synchronous modem using two-bit-per-symbol phase-shift keying (PSK) encoding, achieving 2,000 bit/s half-duplex over normal phone lines.
Increasing modem speed greatly improved the responsiveness of online systems and made file transfer practical.
This led to rapid growth of online services with large file libraries, which in turn gave more reason to own a modem.
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).
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.
[23][24] The ITU-T V.92 standard was approved by ITU in November 2000[25] and utilized digital PCM technology to increase the upload speed to a maximum of 48 kbit/s.
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.
[35] As telephone-based 56k modems began losing popularity, some Internet service providers such as Netzero/Juno, Netscape, and others started using pre-compression to increase apparent throughput.
[36] These accelerated downloads are integrated into the Opera[37] and Amazon Silk[38] web browsers, using their own server-side text and image compression requiring all data to pass through their own servers before reaching the user.
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.
[39] 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.
[44] 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.
[46] 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.
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 DSPs or discrete components.
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.
[50] While traditionally a hardware device, fully software-based modems with the ability to be deployed in a cloud environment (such as Microsoft Azure or AWS) do exist.
[citation needed] 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.
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 term broadband gained widespread adoption in the late 1990s to describe internet access technology exceeding the 56 kilobit/s maximum of dialup.
Their signals are not sent through ordinary phone exchanges, but are instead received by special equipment (a DSLAM) at the telephone company central office.
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.
[57][58] Eventually, ISPs began providing residential gateways which combined the modem and broadband router into a single package that provided routing, 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.
Such systems are an important part of the PSTN, and are also in common use for high-speed computer network links to outlying areas where fiber optic is not economical.
They transmit information that is modulated onto a carrier frequency to allow many wireless communication links to work simultaneously on different frequencies.[relevant?]
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.
Some models are also provided with a microSD memory slot and/or jack for additional external antenna, (Huawei E1762, Sierra Compass 885.
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.
