Page 100 - DCAP406_DCAP_207_Computer Networks

Unit 6: Multiplexing

Self Assessment Notes

State whether the following statements are true or false:
6. The modulation is the act of translating some high-frequency (base band signal) such as
voice, data, etc. to a lower frequency.

7. Amplitude Modulation (AM) involves the modulation of the amplitude of the carrier as
analog sine wave.
8. FM considered a linear process whereas AM as a nonlinear process.

9. In PM the phase of the carrier is made proportional to the instantaneous amplitude of the
modulating signal.
10. Analog to analog signal conversion involves amplitude modulation and frequency
modulation techniques only.

6.6 Summary

A circuit is a path between two or more points along which signals is carried. The circuit
may be a physical path consisting of wires or it may be wireless. A network, which is
wired or wireless involves a number of circuits consisting of a number of intermediate
switches.
A virtual circuit is a logical path selected out of many possible physical paths available
between two or more points.
Multiplexing is the process in which multiple channels are combined for transmission
over a common transmission path.

In FDM multiple channels are combined together for transmission over a single channel.
TDM is a process to merge data from several sources into a single channel for
communication over transmission media like telephone lines, microwave system or
satellite system. Asynchronous TDM is known as Statistical TDM (STDM). The synchronous
TDM technique divides a single channel into time slots and each transmitting device is
assigned at least one of the time slots for its transmission.
CDM is defined as a form of multiplexing where the transmitter encodes the signal using
a pseudo random sequence.
WDM 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.
SDMA is most popular access technology for satellite communication where dish antennas
are frequently and widely employed.
FDMA divides the frequency band into various channels based on the FDM techniques.
Each of these can carry a voice conversation or, with digital service, carry digital data.

TDMA is 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.

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