1. William Stallings Data and Computer Communications 7 th Edition Chapter 8 Multiplexing

3. Multiplexing Categories

4. Frequency Division Multiplexing —Analog signaling is used to transmit the signals. —Broadcast radio and television, cable television, and the AMPS cellular phone systems use frequency division multiplexing. —This technique is the oldest multiplexing technique. —Since it involves analog signaling, it is more susceptible to noise.

5. Frequency Division Multiplexing Diagram

6. Frequency Division Multiplexing Frequency Division Multiplexing (FDM) —Primarily used for Analog data. —Bandwidth of medium equals or exceeds the sum of all channel bandwidths —Each signal is modulated to a different carrier frequency —Carrier frequencies separated so signals do not overlap (guard bands) —Can carry multiple telephone conversations over a single transmission channel. Frequencies in each call are changed so they can be placed side- by-side in a wide-band channel and be transmitted as a group. At the other end, the frequencies in each call are changed back to the original frequencies.

7. Frequency Division Multiplexing Frequency Division Multiplexing (FDM) —More efficient in terms of bandwidth than digital systems. —Downside is that noise is amplified along with the voice. —Has been replaced with Time Division Multiplexing (TDM). —e.g. broadcast radio —Channel allocated even if no data

8. Frequency Division Multiplexing FDM is an analog multiplexing technique that combines signals.

9. Frequency Division Multiplexing Frequency Division Multiplexing (FDM) —Assignment of non-overlapping frequency ranges to each “user” or signal on a medium. —A multiplexor accepts multiple analog inputs and assigns frequencies to each device. Modulation is used to move input signals into the assigned frequency ranges. —The multiplexor is attached to a high-speed communications line. A corresponding demultiplexor on the other end of the line separates the multiplexed signals. —FDM is only used with analog signals.

10. FDM System Figure 8.4

11. FDM of Three Voiceband Signals

12. FDM Process

13. FDM Demultiplexing Process

14. FDM Question #1 Question —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 without the use of guard bands. Solution —Shift (modulate) each of the three voice channels to a different bandwidth, as shown on the next slide.

15. Frequency Division Multiplexing of Three Voice Calls

16. Frequency Division Multiplexing

17. Why stop there? —Group 12 Voice channels Frequency range: 60 – 108 kHz —Super Group 5 Groups 60 Voice channels Frequency range: 312 – 552 kHz —Master Group 10 Super Groups 600 Voice channels Frequency range: 564 – 3084 kHz

18. Frequency Division Multiplexing Why stop there? (cont.) —Jumbo Group 6 Master Groups 3600 Voice channels Frequency range: 564 – 17,548 —Jumbo Group Multiplex 3 Jumbo Groups 10,800 Voice channels Frequency range: 3124 – 60,556 kHz

19. Frequency Division Multiplexing

20. FDM Question #2 Question —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 x 100) + (4 x 10) = 540 KHz (5 x 100) + (4 x 10) = 540 KHz

21. FDM Question #2

22. Time Division Multiplexing —Digital Technology. —Can carry multiple telephone conversations over a single transmission channel. Analog speech signals are sampled and converted to pulses. The samples are then coded by Pulse Code Modulation (PCM) All the samples are transmitted in series over the same channel, one at a time. At the other end, the signals are demodulated and each sample from each channel is routed to the proper channel.

23. Time Division Multiplexing —Sharing of the signal is accomplished by dividing available transmission time on a medium among users. —Digital signaling is used exclusively. —Time division multiplexing comes in two basic forms: —Synchronous time division multiplexing, and —Statistical, or asynchronous time division multiplexing.

24. Time Division Multiplexing

26. TDM System n

27. Wavelength Division Multiplexing Multiple beams of light at different frequency Carried by optical fiber A form of FDM Each color of light (wavelength) carries separate data channel 1997 Bell Labs —100 beams —Each at 10 Gbps —Giving 1 terabit per second (1 Tbps) Commercial systems of 160 channels of 10 Gbps now available Lab systems (Alcatel) 256 channels at 39.8 Gbps each —10.1 Tbps —Over 100km

28. WDM Operation Same general architecture as other FDM Number of sources generating laser beams at different frequencies Multiplexer consolidates sources for transmission over single fiber Optical amplifiers amplify all wavelengths —Typically tens of km apart Demux separates channels at the destination Mostly 1550nm wavelength range Was 200MHz per channel Now 50GHz

29. Dense Wavelength Division Multiplexing DWDM No official or standard definition Implies more channels more closely spaced that WDM 200GHz or less