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Data Communication

Data Communication. Lecture # 08 Course Instructor: Engr. Sana Ziafat. MULTIPLEXING. Multiplexing. Bandwidth utilization is the wise use of available bandwidth to achieve specific goals. Efficiency can be achieved by multiplexing.

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Data Communication

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  1. Data Communication Lecture # 08 Course Instructor: Engr. Sana Ziafat

  2. MULTIPLEXING

  3. Multiplexing • Bandwidth utilization is the wise use of available bandwidth to achieve specific goals. • Efficiency can be achieved by multiplexing. • Multiplexing is the set of techniques that allows simultaneous transmission of multiple signals across a single link. (Many to one or one to many).

  4. Multiplexing vs. No Multiplexing

  5. Note • Link refers to the physical path . • Channel refers to the portion of a link that carries a transmission between a given pair of lines . • One link may have many channels .

  6. How FDM is implemented • Divide the available bandwidth of a single physical medium into a number of smaller , independent frequency channel. • Using modulation , independent message signals are translated into different frequency bands. • All the modulated signals are combined in a linear summing circuit to form a composite signal for transmission. • The carriers used to modulate the individual message signals are called sub-carriers. • Guard bands. -Channels must be separated by strips of unused bandwidth to prevent inter-channel cross-talk.

  7. Figure Frequency-division multiplexing

  8. FDM, Time Domain

  9. Multiplexing, Frequency Domain

  10. Demultiplexing, Time Domain

  11. Demultiplexing, Frequency Domain

  12. Example 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

  13. Figure Example

  14. Example 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 interference? Solution For five channels, we need at least four guard bands. This means that the required bandwidth is at least 5 × 100 + 4 × 10 = 540 kHz,

  15. FDM Application • Transmission of FM (530~1700kHz) • AM radio broadcasting(88~108MHz) • TV broadcasting(6MHz) • Cable television • Advance mobile phone systems(AMPS)

  16. Figure Analog hierarchy

  17. WDM • WDM is designed to use the high data rate capability of fiber optic cable. • WDM is conceptually the same as FDM, except the multiplexing and demultiplexing involves optic signals transmitted through fiber optic channels.

  18. Figure Wavelength-division multiplexing

  19. Figure Prisms in wavelength-division multiplexing and demultiplexing

  20. Time division multiplexing • Time division multiplexing: is a digital process that allows several connections to share the high bandwidth of a link .Each connection occupies a portion of time in the link • TDM is a digital multiplexing technique for combining several low-rate channels into one high-rate one.

  21. Time division multiplexing • The incoming data from each source are briefly buffered. -Each buffer is typically one bit or one character in length -The buffers are scanned sequentially to form a composite data stream. -The scan operation is sufficiently rapid so that each buffer is emptied before more data can arrive.

  22. Figure TDM

  23. Time slots and frames • The data flow of each connection is divided into units , and the link combines one unit of each connection to make a frame. • The size of the unit can be 1 bit or several bits. • For n input connections , a frame is organized into a minimum of n time slots

  24. Time division multiplexing Note • In TDM , the data rate of the link that carries data from n connections must be n times the data rate of a connection to guarantee the flow of data.

  25. Synchronous time-division multiplexing

  26. Note In synchronous TDM, the data rate of the link is n times faster, and the unit duration is n times shorter.

  27. Figure Interleaving

  28. Data Rate Management • Multilevel Multiplexing • Multi-Slot Allocation • Pulse stuffing

  29. Figure Multilevel multiplexing

  30. Figure Multiple-slot multiplexing

  31. Figure Pulse stuffing

  32. Readings Chapter 6 (B. A Forouzan) Section 6.1

  33. Q & A

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