Tuesday, 28 August 2018

4. The Physical Layer

Q. 1. List the responsibilities of Physical layer.
Ans. Bit-signal transformation
         Bit-rate control
         Bit synchronisation
         Mutiplexing

3 comments:

  1. Pratiksha Zambare4 September 2018 at 07:18

    3955,3934,3935,3936,3926,3932,3931,3950,3953
    Q1)Which type of analog & digital signal we use in data communication?
    ->1)Periodic analog signal
    2)Non-periodic signal.

    Q2)How many bits are needed if signal has "1" levels?
    ->logL(to the base 2).

    Q3)What is bit rate?
    ->The bit rate is the number of bits sent in 1 second.

    Q4)What is bit lenght?
    ->The bit length is the distance one bit occupied on the transmission medium.

    Q5)Based on Fourier analysis,a digital signal is______________analog signal?
    1)Opposite 2)parallel to 3)composite 4)perpendicular to
    ->3)composite.

    Q6)List the way to transmit digital signal?
    ->1)Broadband Transmission
    2)Baseband Transmission.

    Q7)What is baseband transmission?
    ->Baseband transmission means sending a digital signal over without changing digital signal to analog signal.

    Q8What is low pass channel?
    ->A channel with a broadband that starts from zero is called low pass.

    Q9)What are signal impairment?
    ->The siganl at the beginning of the medium is not the same as the signal at the end of the medium.

    Q10)What are the causes of impairment?
    ->1)Attenuation 2)Distortion 3)Noise

    Q11)What is attenuation?
    ->Loss of energy is called as attenuation.

    Q12)What is distortion?
    ->Signal changes its form or shape is called as distortion.

    Q13)Whta is value of SNR if the channnel is noiseless?
    ->infinity

    Q14)List the factors on which data rate depends?
    ->1)bandwidth 2)levels of signals 3)quality of channel.

    Q15)Whta is Nyquist bit rate formula for noiseless channel?
    ->bitrate=2 X Bandwidth X logL(to the base 2).

    Q16)What is Shannon capacity formula for noisy channel?
    ->capacity=bandwidth X log(1+SNR)(to the base 2).

    Q17)What is bandwidth in hertz?
    ->Range of frequencies that a channel can pass is called bandwidth in hertz.

    Q18)What is bandwidth bit per second?
    ->Speed of bits transmission in channel or link is called bandwidth in bits per second.

    Q19)What is line coding?
    ->Line coding is the process of converting digital data to digital signal.

    Q20)What is baseline wandering?
    ->The average of recieved signal power is called baseline.A long string of 0's or 1's that cause a drift in the baseline is called as baseline wandering.

    Q21)List the type of line coding scheme?
    ->1)Unipolar 2)Polar 3)Bipolar 4)Multilevel 5)Multitransition.

    Q22)List the data transmission modes?
    ->1)Parallel 2)serial.

    Q23)What is Isochronous serial data transmission?
    ->Tha data arrives at fixed rate without delays between frames is called as Isochronous serial data transmission.

    Q24)List the devices used in physical layer?
    ->1)Repeater 2)Passive hub 3)Active hub.

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  2. Roll no.3903

    Q1.What is NRZ?
    Ans.
    The most straight forward form of digital modulation is to use a positive voltage to represent a 1 and a negative voltage to represent a 0. For an optical fiber,the presence of light might represent a 1 and the absence of light might represent a 0. This scheme is called NRZ (Non-Return-to-Zero).

    Q2- Define
    1) Baseband signal
    2) Passband signal
    Ans.
    1)Signals
    that run from 0 up to a maximum frequen cy are called baseband signals.

    2)Signals
    that are shifted to occupy a higher range of frequencies, as is the case for all wireless transmissions, are called passband signals.

    Q3.List characteristics of Line Coding.
    Ans.
    1- Signal element vs data element.
    2- Signal rate vs data rate.
    3- Bandwidth.
    4- Baseline wandering.
    5- DC components.
    6- Self synchronization.
    7- Built-in error detection.
    8- Immunity to noise & interference.
    9- Complexity.

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  3. Roll no.3928
    Q1.Write 2 advantages of circuit switching?
    Ans.
    1)Onces the circuit has been set up, communication is fast and without error.

    Q2.Define types of Hub?
    Ans.
    Two types of Hubs:-
    1) Passive Hub
    2) Active Hub

    Q3.Define passive hub?
    Ans.
    A passive hub is just a connector. It simply connects all the inputs Data received on any line is sent out across all lines.

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