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Electronics and telecommunicationPurushottam Institute of Engg. And Tech.

Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information.

The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data.

Voice band ModemsSoftmodem (dumb modem)ADSL ModemsDSL ModemsCable ModemsOptical Modems

A voiceband modem that turns the digital 1s and 0s of a personal computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1s and 0s back into a form used by a USB, Ethernet, serial, or network connection.

Winmodem or Softmodem is a stripped-down modem that replaces tasks traditionally handled in hardware with software.

In this case the modem is a simple digital signal processor designed to create sounds, or voltage variations, on the telephone line.

Softmodems are cheaper than traditional modems, since they have fewer hardware components.

Broadband modems should still be classed as modems, since they use complex waveforms to carry digital data.

They are more advanced devices than traditional dial-up modems as they are capable of modulating/demodulating hundreds of channels simultaneously.

Many broadband modems include the functions of a router (with Ethernet and WiFi ports) and other features such as DHCP, NAT and firewall features.

DSL originally stood for digital subscriber loop, although in recent years, the term digital subscriber line has been widely adopted as a more marketing-friendly term for ADSL, which is the most popular version of consumer-ready DSL.

DSL uses high frequency, while regular telephone uses low frequency on the same telephone line.

Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide.

It does this by utilizing frequencies that are not used by a voice telephone call.

A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time.

A cable modem is a type of modem that provides access to a data signal sent over the cable television infrastructure.

Cable modems are primarily used to deliver broadband Internet access in the form of cable internet, taking advantage of the high bandwidth of a cable television network.

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.

Typically, 'up' and 'down' signals are kept separate using frequency division multiple access.

Optical modems transmit data over optical fibers.

Most intercontinental data links now use optical modems transmitting over undersea optical fibers.

Optical modems routinely have data rates in excess of a billion (1x109) bits per second.

Modems are the devices ,those are used in the field of communication to Modulate and Demodulate (As the name itself suggests) signals so as to be transmitted over a communication channel.

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