About Modems
With the evolution of technology, world has contracted in to a small village. One single click on your computer
can connect you to any part of the globe. All of this has been possible due to a small electronic device called
Modem. In this information guide we will discuss in detail about modem, its types, history, working and
other important things.
What is a Modem?
Modem is an electronic device that converts computer's digital information into
analog carrier signals and vice versa. Computers use modems to communicate with
each other over a network. The word modem is derived from "
modulator-
demodulator"
that defines the functions it performs.
How Modem Works?
Modems are
computer hardware typically used to transmit digital data over a phone line.
The working of modems can be easily understood from this. Modems always work in pair.
The sending modem converts computer’s digital information into specific frequencies
compatible with the phone line, the process is called modulation. The receiving modem
decodes the signal back into the digital information, the process is known as demodulation.
In wireless modems, digital data is converted into radio signals and vice versa.
Origin Of Modems
The requirement of communication between distant computers led to the usage of
phone line for data transmission. Since the phone lines were designed to carry
analog information (voices) only and computers and its related
network devices
work in digital form, a interface was needed to bridge this gap, which could act
as a converter between the two systems. The result came in the form of Modems.
Initially modems were primarily used to communicate data between terminals
and a host computer. Later their use was extended to communicate between
end computers. It was around 1960 when modems came into existence. 1960s
were the age of time-shared computers. A business would often buy computer
time from a time-share facility and connect to it via a 300-bit-per-second
(bps) modem. Now modems are used for different functions. Their applications
include textual and voice mail systems, facsimiles, and they are integrated
into cellular phones,
pdas, and notebook computers enabling them to send data
from anywhere. All these needs have increased the modem speed up to 28.8 kbps.
Types of Modem
The classification of modems can be done on the basis of a number of criteria
that includes line type, operation mode, synchronization, modulation, and range.
Keeping aside all these types of modems, in this section we will discuss some
of the most common and popularly used types of modems worldwide.
DSL (Digital Subscriber Line) Modem
DSL modems are the type of modems used to connect a PC to the Internet. These modems
provide fast Internet access as they work on high-speed DSL connections that are
considered much faster than dial-up Internet connections. The foremost advantage
of DSL is its ability to use the phone line to make or receive calls while connected
to the Internet. The traditional dial-up service can't provide this service without
the use of a second phone line. DSL achieves this by adding a filter on the phone
jacks in a location that will have telephones connected to them. A DSL modem provides
similar service to that provided by a dial-up modem, the only exception is the high
speed. But the setup and technological make up of DSL modems differs from the dial
up. Other major difference is that DSL modems are external modems and connects to a
computer via a USB or Ethernet port, while the dial-up modems are usually installed
inside computer terminals.
ADSL (Asymmetric Digital Subscriber Line) Modem
ADSL modem provides faster downloading (getting data) than uploading (sending data).
These modems have significant advantages over the dial-up modems. Like dial up modem it
also uses a standard telephone line but it does not tie up the line. Thus the telephone
line can be used while accessing the Internet. ADSL service is like an "always on"
connection that cannot be left connected indefinitely. ADSL modem is faster than a
dial-up modem. Due to available bandwidth on the dedicated copper wire, ADSL modem
can accommodate a telephone conversation. An ADSL modem needs ADSL service through
an Internet Service Provider (ISP). It can't work with a dial-up account.
SDSL (Symmetric Digital Subscriber Line) Modem
SDSL modems works on SDSL lines that provide equal bandwidth in both directions.
Such types of modems are useful for those businesses which need to upload as well as
download large files or programs to or from the Internet. These modems use voice
traffic lanes to expand bandwidth, and therefore aborting the possibility of a
conversation when the SDSL modem is connected. For this purpose a dedicated phone
line is required.
Cable Modem
Cable modems are the types of modems that uses cable TV wiring
instead of the phone line to provide Internet connectivity. They
provides bi-directional data communication via radio frequency
channels on a cable television infrastructure. Cable modems mainly
deliver broadband Internet access in the form of cable Internet
taking the benefit of the high bandwidth of a cable television network.
Cable modems work on the same principle as the DSL modem. One needs to
have service from a cable TV provider for Internet connectivity and also
some
network cables. The frequencies used for data traffic and TV traffic
do not interfere each other. Cable modems are commonly deployed in Europe,
North and South America, and Australia.
SatModem (Satellite Modem)
One of the least common types of cable modem is a satellite modem, or satmodem.
It is a wireless modem converting digital data into radio waves to communicate
with a satellite dish. This particular type of service is more expensive than
other conventional types of Internet connectivity. Satellite modems can be of
great help for businesses or people in rural areas that do not yet have DSL
or cable service offerings.
Internal Modem
Internal modems are installed inside desktops or
laptop computers,
enabling the computer to communicate with other connected computers
over a network. Internal modems are of two types, dial-up and WiFi.
Dial up modem operates over a telephone line and needs a network access
phone number and log-on credentials to do the connection. A wi-fi modem
can connect wirelessly and without credentials in certain cases.
External Modem
All the modems initially used were external modems. They were in
proprietary use for decades prior to 1981, which marks the release
of the first affordable and practical modem for public use. External
modems are useful in situations when no internal slots are available,
or if the modem needs to be shared between computers that are not networked.
An external modem connected to a desktop system can easily be disconnected
and connected to different
desktop or laptop. External modems for dial-up
service are easy to setup and come with instructions. They are inexpensive
and available at all places where computers are sold. These modems also
include
fax capability at the software level.
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