Codec and demodulator

1. The coder part of the codec and demodulator part of the codec are way too different from each other. Write on some aspects of the difference between both of them.

Answer: Computer data sent over a modem are analog. The analog signals are digitized by a device called a codec . it decoder producing a series of 8-bit numbers. The code makes 8000 codec is for compressing and decompressing data. codec /decoder a device that encodes or decodes a signal. Ex, telephone companies use codec computer data sent over a modem are analog. This type of codec combines analog-to-digital conversion and digital-to-analog conversion functions in a single software, hardware, or a combination

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.

Answer: 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 rationwhich concept is given by Shannon'sin case of noisy channels.
Also it is not applicable to fibre optic cable: In fiber optic cable we transmit the pulse of light and the light is produceddue 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 nyquiest.

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.

Answer: Noise can easily change the amplitude of the signalrather than frequancy . So, Noise affects more AM than FM.

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

a) 1111

b) 0101

c) 0000

d) 1100


0 1 0 1

b) Manchester encoding

Differential Manchester encoding

c) Manchester encoding

Differential Manchester encoding

0 0 0 0

1 1 0 0

d)Manchester encoding

Differential Manchester encoding

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.

Answer: dc component plays an important role in encoding designing. Most long-distance communication channels cannot transport a dc component. The DC component is also called the disparity, the bias, or the dc coefficient. The simplest possible line code, called unipolar because it has an unbounded DC component, gives too many errors on such systems. Most line codes eliminate the DC component— such codes are called DC balanced, zero-DC, zero-bias or DC equalized etc.

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

Answer: Factors:

1: signal to noise ratio: S/N:

S/N = (signal power)/(baseband noise power)

2: Bit error rate: BER:

BER = (number of improperly detected bits during time t) /(total number of bits detected during time t )

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?

Answer: most suitable multiplexing technique is Wavelength-division multiplexing (WDM). Because it capable of multiplying the available capacity of an optical fiber by adding new channels. Each channel on a new wavelength of light. It requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer.

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.

Answer: it is that implementing security at the physical layer is not because a logical connection between two devices may be carried across more than one physical link. Providing host to host security of a connection is more desirable It functions independently of the underlying data transport. These type of security is best implemented at layer 3. The IP layer, since an IP datagram is the smallest addressable unit of data that is carried on an IPnetwork.VPN provides securely transmit data between two network devices over an unsecure data transport medium. It is used to link remote computers or networks to a corporate server via the Internet. It is also the ideal solution for protecting data on a wireless network.

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