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Lecture Data communications and networks: Chapter 6 - Forouzan 

Whether you are collecting numerical statistics from another computer, sending animated pictures from a design workstation, or causing a bell to ring at a distant control center, you are working with the transmission of data across network connections. Chapter 3 discusses the relationship between data, which are created by a device, and electromagnetic signals, which are transmitted over a medium. | Chapter 6 Bandwidth Utilization: Multiplexing and Spreading Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6. Bandwidth utilization is the wise use of available bandwidth to achieve specific goals. Efficiency can be achieved by multiplexing; privacy and anti-jamming can be achieved by spreading. Note 6. 6-1 MULTIPLEXING Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic. Frequency-Division Multiplexing Wavelength-Division Multiplexing Synchronous Time-Division Multiplexing Statistical Time-Division Multiplexing Topics discussed in this section: 6. Figure 6.1 Dividing a link into channels 6. Figure 6.2 Categories of multiplexing 6. Figure 6.3 Frequency-division multiplexing 6. FDM is an analog multiplexing technique that combines analog signals. Note 6. Figure 6.4 FDM process 6. Figure 6.5 FDM demultiplexing example 6. Assume that a voice channel occupies a bandwidth of 4 kHz. We need to combine three voice channels into a link with a bandwidth of 12 kHz, from 20 to 32 kHz. Show the configuration, using the frequency domain. Assume there are no guard bands. Solution We shift (modulate) each of the three voice channels to a different bandwidth, as shown in Figure 6.6. We use the 20- to 24-kHz bandwidth for the first channel, the 24- to 28-kHz bandwidth for the second channel, and the 28- to 32-kHz bandwidth for the third one. Then we combine them as shown in Figure 6.6. Example 6.1 6. Figure 6.6 Example 6.1 6. Five channels, each with a 100-kHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 kHz between the channels to prevent . | Chapter 6 Bandwidth Utilization: Multiplexing and Spreading Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6. Bandwidth utilization is the wise use of available bandwidth to achieve specific goals. Efficiency can be achieved by multiplexing; privacy and anti-jamming can be achieved by spreading. Note 6. 6-1 MULTIPLEXING Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic. Frequency-Division Multiplexing Wavelength-Division Multiplexing Synchronous Time-Division Multiplexing Statistical Time-Division Multiplexing Topics discussed in this section: 6. Figure 6.1 Dividing a link into channels 6. Figure 6.2 Categories of multiplexing 6. Figure 6.3 .