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04 Feb 15
batuj973A modem (modulator-demodulator) is a device that modulates signals to encode digital information and demodulates signals 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. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (symbol bit/s, sometimes abbreviated "bps"), or bytes per second (symbol B/s). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two possible frequencies, corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols (two bits per symbol), transmitted 1,200 bits by sending 600 symbols per second (600 baud) using phase shift keying.-
A modem (modulator-demodulator) is a device that modulates signals to encode digital information and demodulates signals 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. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (symbol bit/s, sometimes abbreviated "bps"), or bytes per second (symbol B/s). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two possible frequencies, corresponding to two distinct symbols (or one bit per symbol), to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols (two bits per symbol), transmitted 1,200 bits by sending 600 symbols per second (600 baud) using phase shift keying.
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26 Mar 14
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to encode digital information
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demodulates the signal to decode the transmitted information.
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can be used with any means of transmitting analog signals
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signals can be transmitted over telephone lines and demodulated by another modem at the receiver side
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28 Jul 13
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Broadband
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DSL modems utilize a property that standard twisted-pair telephone cable can be used for short distances to carry much higher frequency signals than what the cable is actually rated to handle
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DSL modems have a distance limitation.
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DSL's maximum performance gradually declines as the cable length increases.
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29 Dec 12
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09 Oct 12
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A modem (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.
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03 Sep 12
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hat modul
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30 Oct 11
Mark WoodDetail about Modems and different signal conversions
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Broadband
ADSL modems, a more recent development, are not limited to the telephone's voiceband audio frequencies. Some ADSL modems use coded orthogonal frequency division modulation (DMT, for Discrete MultiTone; also called COFDM, for digital TV in much of the world).
Cable modems use a range of frequencies originally intended to carry RF television channels. 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.
New types of broadband modems are beginning to appear, such as doubleway satellite and power line modems.
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.
When broadband technology was introduced, networking and routers were unfamiliar to consumers. However, many people knew what a modem was as most internet access was through dial-up. Due to this familiarity, companies started selling broadband modems using the familiar term modem rather than vaguer ones like adapter or transceiver, or even "bridge".
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30 Sep 11
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handset interfaced with the modem
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26 Sep 11
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A modem (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.
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17 Sep 11
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22 Sep 10
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A modem (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.
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01 Mar 10
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Connection Bitrate (kbit/s) 110 baud Bell 101 modem 0.1 300 baud (Bell 103 or V.21) 0.3 1200 Modem (600 baud) (Bell 212A or V.22) 1.2 2400 Modem (600 baud) (V.22bis) 2.4 2400 Modem (1200 baud) (V.26bis) 2.4 4800 Modem (1600 baud) (V.27ter) 4.8 9600 Modem (2400 baud) (V.32) 9.6 14.4k Modem (2400 baud) (V.32bis) 14.4 28.8k Modem (3200 baud) (V.34) 28.8 33.6k Modem (3429 baud) (V.34) 33.6 56k Modem (8000/3429 baud) (V.90) 56.0/33.6 56k Modem (8000/8000 baud) (V.92) 56.0/48.0 Bonding modem (two 56k modems)) (V.92)[6] 112.0/96.0 Hardware compression (variable) (V.90/V.42bis) 56.0-220.0 Hardware compression (variable) (V.92/V.44) 56.0-320.0 Server-side web compression (variable) (Netscape ISP) 100.0-1,000.0
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Some microwave modems transmit more than a hundred million bits per second
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01 May 08
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09 Feb 08
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23 Nov 07
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