Page 102 - DCAP406_DCAP_207_Computer Networks

Unit 6: Multiplexing

Quadrature Amplitude Modulation: This technique is based on the amplitude modulation Notes
and phase modulation to improve the performance of the amplitude modulation.
Quadrature Phase Shifted Keying: In the case of 4 different phase shifts possibilities for each
symbol which means that each symbol represents 2 bits the modulation will be called
quadrature PSK (QPSK).

Space Division Switching: Refers to the kind of switch developed for analog environment.
Crossbar switch is the simplest possible space division switch where each packet takes a
different path through the switch depending on its destination. Time division switching is
based on multiplexing for digital transmission.
TDM: Refers to the process to merge data from several sources into a single channel for
communication over transmission media like telephone lines, microwave system or satellite
system.

TDMA: This is a digital transmission technology that allows a number of channels to access a
single radio frequency (RF) channel without interference by allocating unique time slots to
each channel.
Virtual circuit: This is a logical path selected out of many possible physical paths available
between two or more points.

WDM: This is defined as the fiber-optic transmission technique that employs two or more
optical signals having different wavelengths to transmit data simultaneously in the same
direction over one fiber, and later on is separated by wavelength at the distant end.

6.8 Review Questions

1. When a channel is called a circuit?
2. How does multi-channeling help broadband transmission?

3. How can a single transmission be shared among different signals? Describe any two
methods.
4. Why are TDM and FDM methods employed for use in the telephone system, but not for
computing networks?
5. What is the purpose of guard band in FDM?
6. How can a single transmission be shared among different signals? Describe any two
methods.
7. Why are TDM and FDM methods employed for use in the telephone system, but not for
computing networks?

8. Why do we normally use a sinusoidal wave as a carrier wave to transmit information?
9. How is it possible to transmit the output produced by a computer over a computer network
connected via telephone lines?

10. What is modulation? How does modulation help in reducing the size of antenna for
transmission?

Answers: Self Assessment

1. Wireless 2. wavelength-division multiplexing
(WDM).

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