1. Chapter 3 : Data transmission
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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 medium and physical layer
A transmission media defined as anything that carry information between a source to a destination
Located below the sender physical layer and is connected to the other receiver physical layer.

6. Classes of Transmission Media

7. 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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8. Transmission Terminology
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9. Transmission Terminology: Types of connections
The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitter to receiver with no intermediate devices,
1-Point –to-point
it provides a direct link between two devices and those are the only two devices sharing the medium.
2- Multipoint
In which more than two devices share the same medium.
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10. Transmission Terminology: Direction of data flow
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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11. 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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12. Time and Frequency Domain
Figure 4-11
Time and Frequency Domain
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 The McGraw-Hill Companies, Inc., 1998

13. Examples  The McGraw-Hill Companies, Inc., 1998 Figure 4-12
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 The McGraw-Hill Companies, Inc., 1998

14. Signal with DC Component
Figure 4-13
Signal with DC Component
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998

15. Complex Waveform  The McGraw-Hill Companies, Inc., 1998 Figure 4-14
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 The McGraw-Hill Companies, Inc., 1998

16. Bandwidth  The McGraw-Hill Companies, Inc., 1998 Figure 4-15
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 The McGraw-Hill Companies, Inc., 1998

17. Digital Signal  The McGraw-Hill Companies, Inc., 1998 Figure 4-16
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 The McGraw-Hill Companies, Inc., 1998

18. Amplitude, Period, and Phase
Figure 4-17
Amplitude, Period, and Phase
for a Digital Signal
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998

19. Bit Rate and Bit Interval
Figure 4-18
Bit Rate and Bit Interval
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998

20. Harmonics of a Digital Signal
Figure 4-19
Harmonics of a Digital Signal
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998

21. Exact and Significant Spectrums
Figure 4-20
Exact and Significant Spectrums
However, most of the energy in the signal is contained in a relatively narrow band of frequencies. This band is referred to as the effective bandwidth, or just bandwidth.
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998
Lte Capacity Workstream RMEA | Ericsson Internal | Uen, Rev DRAFT | 18-May | Page ‹#›

22. Corruption Due to Insufficient Bandwidth
Figure 4-22
Corruption Due to Insufficient Bandwidth
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998

23. Bandwidth and Data Rate
Figure 4-23
Bandwidth and Data Rate
Increasing the Bit Rate result in increasing the BW
كلما زاد ال bit rate كلما زاد ال لb.w
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998
Lte Capacity Workstream RMEA | Ericsson Internal | Uen, Rev DRAFT | 18-May | Page ‹#›

24. DC component
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25. DC component No DC component. DC component = 1 13-Nov-18
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26. Data rate & Bandwidth
Data rate: is the amount of data that is moved from one place to another in a given time.
It is measured in bps , and can be calculated by:
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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27. 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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28. 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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29. 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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30. 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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31. Effect of bandwidth on a digital signal
greater the bandwidth transmitted, the greater the quality.
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32. Units of period and frequency
TABLE 3.1

33. The end
Any Question ?
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