face book

Páginas: 4 (982 palabras) Publicado: 13 de agosto de 2013
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.The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from light emittingdiodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in the voice frequency range of a telephonechannel. These signals can be transmitted 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 theycan send in a given unit of time, usually expressed in bits per second (bit/s, or bps), or bytes per second (B/s). Modems can alternatively be classified by their symbol rate, measured in baud. Thebaud 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 frequenciescorresponding 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 was able to transmit and receive fourdistinct symbols (two bits per symbol), handled 1,200 bit/s by sending 600 symbols per second (600 baud) using phase shift keying.
El término banda ancha comúnmente se refiere al acceso de alta velocidada Internet. Este término puede definirse simplemente como la conexión rápida a Internet que siempre está activa. Permite a un usuario enviar correos electrónicos, navegar en la web, bajar imágenes ymúsica, ver videos, unirse a una conferencia vía web y mucho más. El acceso por banda ancha es más rápido que la conexión de acceso telefónico y es diferente por lo siguiente:
El servicio de banda...
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