1. Chapter 3 : Data transmission
Networks and Communication Department
Data and Communication book by William stalling

2. Lecture Contents 3.1 Concepts and Terminology The Physical Layer.
Transmission Terminology.
Spectrum and Bandwidth.
DC component
Data Rate an Bandwidth.
Digital signal and Bandwidth.
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3. 3.1 Concepts and Terminology
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4. The Physical Layer Foundation on which other layers build
Properties of wires, fiber, wireless limit what the network can do
Key problem is to send (digital) bits using only (analog) signals
This is called modulation
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5. Transmission Terminology:
The successful transmission of data depends on two factors:
quality of the signal being transmitted
characteristics of the transmission medium
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6. Transmission Terminology
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7. Transmission Terminology
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8. Transmission Terminology
Simplex :
signals transmitted in one direction
eg : Television
Half duplex:
both stations transmit, but only one at a time
eg : Police radio
Full duplex:
simultaneous transmissions
eg : Telephone
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9. Spectrum & Bandwidth range of frequencies contained in signal spectrum
width of spectrum
Absolute bandwidth
narrow band of frequencies containing most energy
often just bandwidth
Effective bandwidth
component of zero frequency
dc component
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10. DC component
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11. DC component No DC component. DC component = 1 30-Nov-18
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12. Data rate & Bandwidth
Data rate: is the amount of data that is moved from one place to another in a given time.
(bps) , Data rate=2*f
Bandwidth: is the actual speed at which data can be transmitted on a connection.
There is a direct relationship between data rate & bandwidth
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13. Data Rate Calculation
Suppose that we are using a digital transmission system that is capable of transmitting signals with a bandwidth of 12 MHz
From the figures, What data rate can be achieved?
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14. Data Rate Calculation Fig . A : Fig . B : BW = 5f – f
12 MHz = 5f – f  f = 3 MHz
Data rate = 2 * f = 2 * 3 = 6 Mbps
Fig . B :
BW = 7f – f
12 MHz = 7f – f  f = 2 MHz
Data rate = 2 * f = 2 * 2 = 4 Mbps
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15. Data rate & Bandwidth relationship
any transmission system has a limited band of frequencies
this limits the data rate that can be carried on the transmission medium
square waves have infinite components and hence an infinite bandwidth
most energy in first few components
limiting bandwidth creates distortions
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16. Data rate & Bandwidth relationship
In general :
any digital waveform will have infinite bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted.
On one hand, for any medium, the greater the bandwidth transmitted, the greater the cost.
On the other hand limiting the bandwidth creates distortions, and the greater the potential for error by the receiver.
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17. Effect of bandwidth on a digital signal
greater the bandwidth transmitted, the greater the quality.
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18. The end
Any Question ?
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