The Codec And Demodulator Computer Science Essay

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Computer data sent over a modem are analog. The analog signals are digitized in the end office by a device called a codec coder - decoder producing a series of 8-bit numbers. The code makes 8000 codec is any technology for compressing and decompressing data.In telecommunications, short for coder/decoder a device that encodes or decodes a signal. For example, telephone companies use codecs. This type of codec combines analog-to-digital conversion and digital-to-analog conversion functions in a single chip. In personal and business computing applications, the most common use for such a device.

An endec (encoder/decoder) is a similar yet different concept mainly used for hardware. In the mid 20th century, a "codec" was hardware that coded analog signals into Pulse-code modulation (PCM) and decoded them back. Late in the century the name came to be applied to a class of software for converting among digital signal formats, and including compander functions.

A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Codecs are used in videoconferencing and streaming media applications. A video camera's analog-to-digital converter (ADC) converts its analog signals into digital signals, which are then passed through a video compressor for digital transmission or storage. A receiving device then runs the signal through a video decompressor, then a digital-to-analog converter (DAC) for analog display. The term codec is also used as a generic name for a video conferencing unit.

An audio compressor converts analog audio signals into digital signals for transmission or storage. A receiving device then converts the digital signals back to analog using an audio decompressor, for playback. An example of this are the codecs used in the sound cards of personal computers.

2. The Nyquist theorem is one of the deciding factor in data communication. The fibre optics as well as the copper wires are communication mediums. Do you think the theorem is valid for the fiber optics or for the copper wires.

ANS: The Nyquist theorem is not applicable to copper wire.  Because it is applicable to noiseless channel. The bandwidth of a copper wire depends on the cable quality, length, and signal to noise ratio of data transmitted. As we see copper bandwidth is directly depends upon the signal to noise ration  which concept is given by Shannon's  in case of noisy channels.

Also it is not applicable to fiber optical cable: In fiber optic cable we transmit the pulse of light and the light is produced  due to the motion of molecules throughout the system that creates much noise. To calculate the noise created per signal we uses the concept of signal to noise ratio that is given by shanon;s not by nyquist.

3. Noise affects all the signals which are there in air. There are some communicating modulation techniques. Noise affects which of the modulation technique the most.

Ans= Amplitude Modulation is the most prone to noises. It is the high bandwidth of FM that allows the effects of noise to be minimized.

4. Convert the following bit stream using Manchester and differential modulation techniques.

a) 1111

b) 0101

c) 0000

d) 1100

5. The DC component plays a role in designing encoding scheme. Can we relate the DC component's effect on all the encoding schemes? Justify your answer by giving an example.

ANS: there is important role of dc signal when we creating the coding schemes. but when the voltage level in the digital signal is constant for a while the spectrum creates a very low frequency .these frequencies around zero called dc components, present problems for a system that can not pass low frequency or a sstem that uses electrical coupling .for example, a telephone line can not pass the low frequency below 200Hz. also a long distance link may use one or more transformer to isolate different parts of the line electrically. for these system we need a scheme with no dc components.

6. Multiplexing technique is used for combining the multiple channels into one channel. Write the factors on which the combination is happening.

ANS: Multiplexing is the set of techniques that allows the transmission of multiple signal across a single data link. there are many basic multiplexing techniques ; frequency-division multiplexing, wavelength -division multiplexing and the time division multiplexing. The first two technique designed for analog signal and the third, for digital signals.

Frequency-division multiplexing: it is an analog technique that can be applied when the bandwidth of a link is greater than the the combined bandwidths of the signals to be transmitted .guard band is used to save signal from overlapping .

Its application is AM and FM broadcasting .its also uses in cellular phone.

Wavelenth-division multiplexing : it is designed to use the high -data rate capability of fiber optic cable. the optical data rate is higher than the copper cables.its uses in the SONET network in which multiple optical fiber lines are multiplexed and demultiplexed.

Time -division multiplexing: it is a digital multiplexing technique for combining several low rate channels into one high rate one. in this time is shared b\w the all the sources.

7. There are numerous multiplexing techniques available. What in your opinion is the most appropriate multiplexing technique for the fiber optics as well as copper wires?

ANS: Wave or Wavelength Division Multiplexing (WDM) is used with fibre optic cables. WDM is a technology that closely resembles frequency division multiplexing, but is specifically used to combine lots of Optical Carrier signals into a single optical fibre.

The WDM technique relies on a laser that is designed to emit single colours of light. Each of the signals that is to be transmitted is then attached to a laser that will emit a different coloured light beam. All these individual light beams are then sent at the same time. At the receiving end, a device splits the combined colours back into the original individual colours again.

Frequency division multiplexing is used in the copper wires due to their changing band width. Frequency Division Multiplexing (FDM) works by transmitting all of the signals along the same high speed link simultaneously with each signal set at a different frequency. For FDM to work properly frequency overlap must be avoided. Therefore, the link must have sufficient bandwidth to be able to carry the wide range of frequencies required. The demultiplexor at the receiving end works by dividing the signals by tuning into the appropriate frequency.

FDM operates in a similar way to radio broadcasting where a number of different stations will broadcast simultaneously but on different frequencies. Listeners can then "tune" their radio so that it captures the frequency or station they want.

FDM gives a total bandwidth greater than the combined bandwidth of the signals to be transmitted. In order to prevent signal overlap there are strips of frequency that separate the signals. These are called guard bands.

8. While transferring the data from the transmission medium there are various aspects of your data getting tempered by other users. What in your opinion is the most secure and insecure transmission medium? Justify your answer with an example.

ANS: we know that the data is transfer from guided or unguided medium .but we know that data which is transfer through the the cables in form of analog or digital signal.

But the data which is transfer through the cables is more secure because there is a direct connection between the server and the host .the other host can not access the data because there is some security key or physical address which is send by the server to client .the data transfer rate is also high.

The data which is transfer through the unguided medium by the radio or micro waves is not safe for the host .if we want to secure the data then we have to send the data in form of encrypted form. This is security way to send the data.

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