Chapter 1 Homework 1. What is a circuit? Describe the two-wire and four-wire cir

Question

Chapter 1       Homework     

1.      What is a circuit?  Describe the two-wire and four-wire circuits.  What device boosts a weak signal (analog/digital)?

2.      What is a channel?  Distinguish between a CPE switch and a Network switch.

3.      Define virtual circuits (VCs) and PVCs.

4.      Define frequency, wavelength, amplitude, phase, and bandwidth.

5.      Discuss the characteristics of analog and digital networks.

6.      Describe how digital signals are transmitted over an analog circuit and analog signals over digital circuit.

7.      Differentiate between the following multiplexing techniques in terms of mechanics, technology, and applications.

(a)  FDM;              (b)  TDM;        (c)  STDM

What are the key shortcomings of TDM and how does STDM seek to overcome these?

8.      Describe WDM/DWDM.

Explanation / Answer

1) Circuit: A circuit can be defined as a closed path made of different wires, conductors and/or many other components.

Two wire circuit: It is transmission model which uses a pair of wires leading for the bi-directional traffic of signals. Example for this is a telephone line where people can talk simultaneously. In order to prevent problems occurred by echoes, impedance of components on either sides should be matched with eachother carefully.

Four wire circuit: It is a transmission model which uses two pairs of communication wires for the signal transmission in bi-directional format at the same time. An Ethernet connection is an example for a four-wire circuit.

An amplifier boosts a weak signal.

2)Channel: A particular wide range of frequency used for transmission is called a channel.

3)Virtual circuit: A connection between devices in a network in computer networks and as well as telecommunications.A VC switches back and forth between various circuits for creation of different paths.

PVC: A permanent virtual circuit is a connection between two points which is software defined.

4)Frequency: It is counted as the number of events/occurrences happening in a fixed/limited time span. Units for frequency is Hertz(HZ).

Wavelength: The distance between two consecutive nodes or antinodes of a wave. It is mentioned as lamda. wavelength is inversely proportional to frequency.

Amplitude: It is defined as the maximum point of displacement of a particle from it's position of rest.

Phase: It denotes a specific point in the cycle of a waveform. It is measured as an angle. This is represent using theta.

Bandwidth:Bandwidth is the measurement of received signal in terms of bits per second.

5)Analog transmission: An analog wave is a continuously variable in both amplitude and freqyency. It supports a limited bandwidth which leads to non-support situation for a high speed data. As the distance of the transmission increases, the power of the signal decreases and becomes impaired due to moisture in cables, dirt and etc., Attenuation of the signal is done very easily. This can be solved using an amplifier but an amplifier includes some noise too. Because of this you can end up with a very high error rate.

Digital transmission: A digital transmission is a series of discrete pulses representing binary bits. They can support high spped data and transfer of multimedia stuff. Multiplexers are enable for multiple conversations to share a channel and this leads for a better transmission efficiency.

6) Transcoding: it's a technique of converting analog to digital signals and vice versa. Using this technique, the analog signals can be carried over digital circuits and vice versa.

7)FDM:Frequency-division multiplexing is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel. A typical analog Internet connection via a twisted pair telephone line requires approximately 3kHz of bandwidth for a better data transfer. Twisted-pair lines are common in households and small businesses. But major telephone cables, operating between large businesses, government agencies are capable of much larger bandwidths.

TDM:Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration. Each individual data stream is reassembled at the receiving end based on the timing.The circuit that combines signals at the source end of a communications link is known as a multiplexer. It accepts the input from each individual end user, breaks each signal into segments, and assigns the segments to the composite signal in a rotating, repeating sequence. The composite signal thus contains data from multiple senders. At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users. A two-way communications circuit requires a multiplexer/demultiplexer at each end of the long-distance, high-bandwidth cable.

STDM: --work on it--

8) WDM:It's a technology which multiplexes a number of sinals in to a single transmission fiber. This is done suing different wavelengths so they don't overlap with eachother. This technique even supports the transmission in both directions. It increases the capacity with out losing it's efficiency. DWDM is based on the same concept.

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