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Chapter 6. Multiplexing

Chapter 6. Multiplexing. FDM WDM TDM. Multiplexing: Dividing a Link into Channels. Categories of Multiplexing. Frequency Division Multiplexing. Signals modulate different carrier frequencies Modulated signals are combined into a composite signal

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Chapter 6. Multiplexing

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  1. Chapter 6. Multiplexing FDM WDM TDM Data Communications, Kwangwoon University

  2. Multiplexing: Dividing a Link into Channels Data Communications, Kwangwoon University

  3. Categories of Multiplexing Data Communications, Kwangwoon University

  4. Frequency Division Multiplexing • Signals modulate different carrier frequencies • Modulated signals are combined into a composite signal • Channel - Bandwidth range to accommodate a modulated signal • Channels must be separated by strips of unused bandwidth (guard band) to prevent overlapping Data Communications, Kwangwoon University

  5. FDM Process Data Communications, Kwangwoon University

  6. FDM Demultiplexing Example Data Communications, Kwangwoon University

  7. FDM: Example 1 Data Communications, Kwangwoon University

  8. FDM: Example 2 Data Communications, Kwangwoon University

  9. FDM: Example 3 Data Communications, Kwangwoon University

  10. Analog Hierarchy Data Communications, Kwangwoon University

  11. Wave Division Multiplexing • Conceptually the same as FDM • Light signals transmitted through fiber optic channels • Combining different signals of different frequencies (wavelengths) Data Communications, Kwangwoon University

  12. Prisms in WDM • Combining and splitting of light sources are easily handled by a prism • Prism bends a light beam based on the incidence angle and the frequency Data Communications, Kwangwoon University

  13. Time Division Multiplexing • Portions of signals occupy the link sequentially Data Communications, Kwangwoon University

  14. TDM Data Communications, Kwangwoon University

  15. TDM: Example 1 • Four 1-Kbps connections are multiplexed together. A unit is 1 bit. Find (1) the duration of 1 bit before multiplexing, (2) the transmission rate of the link, (3) the duration of a time slot, and (4) the duration of a frame? 1. The duration of 1 bit is 1/1 Kbps, or 0.001 s (1 ms). 2. The rate of the link is 4 Kbps. 3. The duration of each time slot 1/4 ms or 250 ms. 4. The duration of a frame 1 ms. Data Communications, Kwangwoon University

  16. Interleaving • Interleaving can be done by bit, by byte, or by any other data unit • The interleaved unit is of the same size in a given system Data Communications, Kwangwoon University

  17. TDM: Example 2 Data Communications, Kwangwoon University

  18. TDM: Example 3 Data Communications, Kwangwoon University

  19. Framing Bits Data Communications, Kwangwoon University

  20. TDM: Example 4 • We have four sources, each creating 250 characters per second. If the interleaved unit is a character and 1 synchronizing bit is added to each frame, find (1) the data rate of each source, (2) the duration of each character in each source, (3) the frame rate, (4) the duration of each frame, (5) the number of bits in each frame, and (6) the data rate of the link. 1. The data rate of each source is 2000 bps = 2 Kbps. 2. The duration of a character is 1/250 s, or 4 ms. 3. The link needs to send 250 frames per second. 4. The duration of each frame is 1/250 s, or 4 ms. 5. Each frame is 4 x 8 + 1 = 33 bits. 6. The data rate of the link is 250 x 33, or 8250 bps Data Communications, Kwangwoon University

  21. Bit Padding • The time slot length is fixed • Different data rates must be integer multiples each other • When the speeds are not integer multiples of each other, bit padding is used • In bit padding, the multiplexer adds extra bits to a device’s source stream Data Communications, Kwangwoon University

  22. DS Hierarchy Data Communications, Kwangwoon University

  23. DS and T Line Rates Data Communications, Kwangwoon University

  24. T-1 Line for Multiplexing Telephone Lines Data Communications, Kwangwoon University

  25. T-1 Frame Structure Data Communications, Kwangwoon University

  26. E Line Rates Data Communications, Kwangwoon University

  27. Inverse TDM • Breaks one high-speed line into several lower-speed lines • High-rate data (video, for example) can be inversely multiplexed over multiple lines Data Communications, Kwangwoon University

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