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DCN386-Questions - 1(6 marks Contrast Analog Transmission...

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1. (6 marks) Contrast Analog Transmission with Digital Transmission. Analog transmission is a method of conveying voice, data, image, signal, or video information through waves. It uses a continuous signal varying in amplitude, phase , and frequency. Analog transmission could mean that the transmission is a transfer of an analog source signal which uses an analog modulation method (or a variance of one or more properties of high frequency periodic waveform, also known as a carrier signal). FM and AM are examples of such a modulation. The transmission could also use no modulation at all. It is most notably an information signal that is constantly varying. Digital transmission is quite different from analog transmission. For one thing, the signal is much simpler. Rather than being a continuously variable wave form, it is a series of discrete pulses, representing one bits and zero bits and they use square wave. Each computer uses a coding scheme that defines what combinations of ones and zeros constitute all the characters in a character set . Digital Transmission Digital transmission has several advantages over analog transmission: 1. Analog circuits require ampli_ers, and each ampli_er adds distortion and noise to the signal. 2. In contrast, digital ampli_ers regenerate an exact signal, eliminating cumulative errors.An incoming (analog) signal is sampled, its value is determined, and the node then generates a new signal from the bit value; the incoming signal is discarded. With analog circuits, intermediate nodes amplify the incomiing signal, noise and all. 3. Voice, data, video, etc. can all by carried by digital circuits. What about carrying digital signals over analog circuit? The modem example shows the di_culties in carrying digital over analog. C Analog vs. Digital Transmission Compare at two levels: 1. Data|continuous (audio) vs. discrete (text) 2. Signaling|continuously varying electromagnetic wave vs. sequence of voltage pulses. Also Transmission|transmit without regard to signal content vs. being concerned with signal content. Di_erence in how attenuation is handled, but not focus on this. Look at Table 2.3 and Fig 2.13 in Stallings. Seeing a shift towards digital transmission despite large analog base. Why? _ improving digital technology _ data integrity. Repeaters take out cumulative problems in transmission. Can thus transmit longer distances. _ easier to multiplex large channel capacities with digital _ easy to apply encryption to digital data _ better integration if all signals are in one form. Can integrate voice, video and digital data.
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CS 513 1 week2-physcont.tex Analog Transmission Phone System Because of the role played by phone companies in data transmission, analog transmission has dominated communications for quite some time. Today, everyone agrees that _ber is the way to go. As much as we prefer _ber, analog communications will be with us for a long time. Consider the phone system. It is characterized by: 1. Low bandwidth: It carries a bandwidth of about 3 kHz. That is, the system only
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DCN386-Questions - 1(6 marks Contrast Analog Transmission...

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