Introduction
The 20th century is characterized by a rapid development of science and technologies, particularly in well-developed countries. One of the most significant areas where human knowledge and experience is particularly important is computer technologies, informational technologies, Internet and modern means of communication. In fact the technological achievements in this sphere have changed the contemporary world since nowadays due to the development of high technologies, particularly IT and Internet made geographical borders less significant than ever before.


This technological leap could hardly be possible without such a simple and in the same time sophisticated device as a modem. A modem was absolutely essential for the work of Internet and it still remains quite important for international and interpersonal communication as an effective mean of transition of data.
The role of such an important device needs to be researched and properly evaluated. In order to fulfill this task it is necessary to discuss the history of a modem and its development since the moment of its creation as well as it is necessary to understand the technology applied in a modem and the entity of its functioning and work. All this information is very helpful in understanding perspectives of a modem in the context of recent achievements in technologies and its future.
This is exactly what will be done in terms of this paper and it is supposed that the role of a modem will be clearly understood and its development will continue since even nowadays it is obvious that without a modem it is quite difficult to imagine the contemporary world.
The definition of a modem, its types and principles of work
Obviously, it is necessary to start with the understanding of the notion of a modem since in order to understand the role and place of something in history it is necessary to clearly define what it is. In fact, a modem is defined quite precisely and there are practically no discussions as for its definitions. As a rule a modem is defined as “a device for transmitting usually data over telephone wires by modulating the data into an audio signal to send it and demodulating an audio signal into data to receive it” .
However, such a definition may be viewed as too specific and in some situations it cannot be used consequently there should be a more universal definition. The following one may be considered as such: “a modem is a device that modulates a carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information” .
In fact the entity of the notion of a modem may be understood from the name of the device since an acronym for MOdulator-DEModulator and these two words are key words in the definition of the device.
The principle goal of the functioning of a modem is to produce a signal in a coded form, which eventually may be transmitted and decoded to produce the original message. As a rule modems are used in computing, with the help of modems connecting computers, which may be situated even in different parts of the world, occurs. Traditionally, information that is stored in computers is in a digital form, while information transmitted with the help of modems via telephone lines is transmitted in the form of analog waves. What modem function is, is to convert between these two forms.
To put it more precisely and more understandable form the example with ordinary personal computers may be used, when “a modem turns digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone System (POTS), and once received on the other side, converts those sounds back into 1s and 0s” .
In fact there are different types of modems that are currently used. For instance, practically everybody nowadays may use a modem while surfing Internet. In telecommunications, for instance, a ‘radio modem’ is used, which transmits repeating frames of data at every high data rates over microwave radio links.
Or else, optic modems become more and more popular nowadays and in such type of modems data are transmitted over optic fibers. Currently such modems are used in intercontinental links since they are more effective than traditional ones. Optic modems usually use “interferometric filters called etalons to separate different colors of light, and then individually turns the pulses of each color of light into electronic digital data streams” . These modems are considered to be very fast since their data rates excess of a billion bits per second . However, their bandwidths are limited by the thermal expansion of etalons that leads to the change of their size and consequently frequency.
Anyway nowadays modems are widely spread and are used practically everywhere where they can possibly be used in any means of transmitting analog signals, from driven diodes to radio.
History of a modem
Naturally it is necessary to analyze thoroughly the history of a modem in order to better understand its entity, current use and future perspectives.
At first glance it may be a bit strange that modems were initially used in air industry in 1950s, where they were used to connect terminals located in different airbases, radar sites and command-and-control centers to director centers. First countries, which have started to use modems since 1950s, were the US and Canada. Later, the cooperation between American airlines and IBM led to the development of an automated airline ticketing system . In this system the terminals “were located at ticketing offices, tied to a central computer managed availability and scheduling” . So, 1950s were the period of the first implementation of modems.
The following decade, 1960s was marked by an unparalleled development of computing and IT. At this period the commercial use of computers has become particularly important as never before. Such a ‘computer boom’ resulted in implementation of modem technologies earlier used in air industry into computing industry, where modems have become very popular and useful. In 1962 the first commercial modem was released, it was called the Bell 103. This modem used frequency-shift keying, where two tones were used to encode and decode 1s and 0s of digital data. It is quite noteworthy that the Bell 103 had a transmission rate of 300 bits per second that seems to be quite amusing nowadays.
Soon after the implementation of the first commercial modem its modification have appeared, which were better and faster. In such a way within 1960s modems evaluated from Bell 103, with data rate to 300 bits per second, to the Bell 212, with data rate to 1200 bits per second, and finally the Bell 202, which used both sets of signal on 4-wire leased lines for 2400 bits per seconds.
The next step in the development of modems was the invention in 1977, to a certain extent revolutionary modem for personal computers, developed by Dennis C. Hayes and which symbolized “the emergence of the online and Internet era” . In 1981, the Hayes Smartmodem was introduced. It was a simple 300 bit/s modem using the Bell 103 signaling standards, but attached to a small controller that let the computer to send commands to it to operate the phone line.
The principal difference between the Smartmodem and its predecessors was that in the Smartmodem, instead of manual dial the remote number on a standard phone handset, then plugging the handset into a modem-attached acoustic coupler, “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” . Another very significant advantage of modems that started to appear in 1980s, was their compatibility with previous models and they could support practically all existing standards and by the late 1980s, 2400 bit/s was becoming common. At the same time other standards were amply introduced, for instance it has become common that a high-speed channel was used for receiving while low-speed channel was used for sending .
In such a situation when data rate was permanently growing, American companies have achieved particularly remarkable results and their high-speed lines reached 9600 bit/s.
However, such a dramatic growth of speed resulted in the problems in phone lines. In fact these speeds “pushed the limits of the phone lines, and would have been generally very error-prone” . Naturally the need in the development of error correction system became obvious. In response to this problem a number of error correction systems were developed, among which the most impressive results achieved 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” , while MNP5 was even more revolutionizing since with this product compression was added to the system and in such a way the data rate increased .
In the same time, in 1980s optic fiber manufacturing was significantly improved that provided modem producers to implement these technologies in modems. At first such systems simply used light emitting diodes and PIN diodes. The development of optic fiber and their implementation in modem production led to the possibility to introduce multispectral optic modems.
Recent developments and perspectives of a modem
1990s may be called the ‘Golden Age’ of modems since within only a decade they were perfected on the basis of achievements of late 1980s and they are the basis for further development of modems.
Probably one of the most significant achievements of the late 1980s that was developed in the next decade was the invention of echo cancellation. Despite all innovations that have been done before there still remained a problem since the modem system sends a small amount of the outgoing signal, called sidetone, back to the earphone, in order to provide the user with feedback that their voice is really being sent. Unfortunately such a system confused a modem since the devices could not clearly define whether it was ‘hearing’ from a remote modem, or its own signal being sent back to itself. In such a situation, echo cancellation turn to be a really effective way out since due to it “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 a result, modems could send at full speed in both directions in the same time that eventually lead to the increase of speed from 9600 bit/s to 56kbit/s that is currently used.
However, one of the most perspective trends in modem development is considered to be a wireless modem that is supposed to replace in future currently functioning modems. Recently there have been developed wireless modems of different types, speed and bandwidths. Traditionally wireless modems are referred to as smart or transparent modems. In fact they “transmit information that is modulated onto a carrier frequency to allow many simultaneous wireless communication links to work simultaneous on different frequencies” .
Finally, one of the most recent developments are ADSL modems. One of the most significant advantages of ADSL modems is the fact they are not bound to the telephone’s voice band audio frequencies. Moreover, “some ADSL modems use coded orthogonal frequency division modulation” . In fact ASDL modems use technologies which were supposed to use in television. To put it more precisely, cable modems use a range of frequencies originally intended to carry RF television channels. Furthermore, 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. In order to keep up and down signals separate frequency division multiplexing is used.
In the nearest perspective new types of modems are beginning to appear, such as double way satellite and power line modems that would definitely improve the effectiveness of modems in the future.

Bibliography:
1. Atkinson, J. Modem in the Modern World. New York: McGraw Hill, 2001.
2. Gilbert, L. The Development of IT in the 20th Century. LA: Touchstone, 1999.
3. Fowler, G. The History of a Modem. New York: New Publishers, 2003.
4. Lawrence, P. Computers and IT. New York: New Publishers, 2001.
5. Stuart, W. The Future of a Modem. LA: Touchstone, 2000.

Quotes:
“a device for transmitting usually data over telephone wires by modulating the data into an audio signal to send it and demodulating an audio signal into data to receive it”
“a modem is a device that modulates a carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information”
“a modem turns digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone System (POTS), and once received on the other side, converts those sounds back into 1s and 0s”
“interferometric filters called etalons to separate different colors of light, and then individually turns the pulses of each color of light into electronic digital data streams”
“were located at ticketing offices, tied to a central computer managed availability and scheduling”
“the emergence of the online and Internet era”
“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”
“pushed the limits of the phone lines, and would have been generally very error-prone”
“each slowing the effective data rate by a smaller amount each time, from about 25% in MNP1, to 5% in MNP4”
“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”
“transmit information that is modulated onto a carrier frequency to allow many simultaneous wireless communication links to work simultaneous on different frequencies”
“some ADSL modems use coded orthogonal frequency division modulation”

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