1 Multiplexing Multiplexing process allows several transmission sources to share a larger transmission capacity multiple links on 1 physical line Most common use of multiplexing is in longhaul communication using coaxial cable microwave and optical ID: 1030645
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1. MultiplexingChapter 8Networks and Communication Department1
2. MultiplexingMultiplexing process allows several transmission sources to share a larger transmission capacity.multiple links on 1 physical lineMost common use of multiplexing is in long-haul communication using coaxial cable, microwave and optical fibre
3. MultiplexingThe multiplexer combines (multiplexes) data from the n input lines and transmits over a single data link(medium). The demultiplexer separates (demultiplexes) the data according to channel, and delivers data to the appropriate output lines.
4. Multiplexing Types14-Nov-17Networks and Communication Department4Multiplexing :The set of techniques that allows the simultaneous transmission of multiple signals across a single data link. It has the following types:1. Frequency-Division Multiplexing (FDM)2. Wavelength-Division Multiplexing (WDM)3. Time-Division Multiplexing (TDM)4. Code-Division Multiplexing (CDM)
5. Frequency Division Multiplexing5Networks and Communication Department14-Nov-17
6. Frequency Division MultiplexingFDM can be used with analog signalsPut different signals on different frequency bands using modulations.each signal is modulated onto a different carrier.All the modulated signals are combined to form a composite signal for transmission.signals are carried simultaneously on the same mediumTo prevent interference, the channels are separated by guard bands, which are unused portions of the spectrum.
7. Frequency Division MultiplexingA general case in Figure 8.2a. Six signal sources are fed into a multiplexer, which modulates each signal onto a different frequency (f1, …, f6).
8. FDMSystem Overview
9. Frequency Division MultiplexingTelevision and radio uses FDM to broadcast many channels over the same media.
10. Frequency Division Multiplexing14-Nov-17Networks and Communication Department10
11. Wavelength Division MultiplexingTheoretically identical to Frequency Division Multiplexing.Used in optical systems while FDM is usedin electrical systems.Requires more spacing between channelsalso have Dense Wavelength Division Multiplexing (DWDM)
12. Wavelength Division Multiplexing
13. Time-Division Multiplexing (TDM)14-Nov-17Networks and Communication Department13multiple transmissions can occupy a single link by subdividing them and interleaving the portions. TDM can be implemented in two ways:1. Synchronous TDM2. Asynchronous TDM
14. Synchronous Time Division Multiplexing14Networks and Communication Department14-Nov-17
15. Synchronous Time Division Multiplexingcan be used with digital signals or analog signals carrying digital data. In this form of multiplexing, data from various sources are carried in repetitive frames. Each frame consists of a set of time slots, and each source is assigned one or more time slots per frame.Synchronous TDM is called synchronous not because synchronous transmission is used, but because the time slots are preassigned to sources and fixed.
16. Synchronous Time Division Multiplexing14-Nov-17Networks and Communication Department16The multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.A frame consists of one complete cycle of time slots.Thus the number of slots in frame is equal to the number of inputs.
17. Synchronous Time Division MultiplexingFor example, the multiplexer in Stallings DCC8e Figure 8.2b has six inputs that might each be, say, 9.6 kbps. A single line with a capacity of at least 57.6 kbps (plus overhead capacity) could accommodate all six sources.
18. How Synchronous TDM Works14-Nov-17Networks and Communication Department18
19. Statistical Time Division Multiplexing19Networks and Communication Department14-Nov-17
20. Asynchronous TDM(or statistical time-division multiplexing14-Nov-17Networks and Communication Department20Each slot in a frame is not dedicated to the fix deviceThe number of slots in a frame is not necessary to be equal to the number of input devices.More than one slots in a frame can be allocated for an input device.Asynchronous TDM (or statistical time-division multiplexing) Allows maximum utilization of the link.It allows a number of lower speed input lines to be multiplexed to a single higher speed line
21. Statistical TDMin Synch TDM many slots are wastedStatistical TDM allocates time slots dynamically based on demandmultiplexer scans input lines and collects data until frame fullline data rate lower than aggregate input line rates may have problems during peak periodsmust buffer inputs
22. Statistical TDM Frame Format
23. How Asynchronous TDM Works?14-Nov-17Networks and Communication Department23In asynchronous TDM, a frame contains a fix number of time slots. Each slot has an index of which device to receive.
24. Synchronous vs. Statistical TDM
25. Multiplexing Real Examples14-Nov-1725Networks and Communication Department
26. Asymmetrical Digital Subscriber Line (ADSL)Digital Subscriber Line is the link between subscriber and networkIt uses currently installed twisted pair cableThe term asymmetric refers to the fact that ADSL provides more capacity downstream (from the carrier’s central office to the customer’s site) than upstream (from customer to carrier), being a good fit to Internet requirements.is Asymmetric - bigger downstream than upuses Frequency division multiplexinghas a range of up to 5.5km
27. Code Division Multiplexing14-Nov-1727Networks and Communication Department
28. Code Division Multiplexing14-Nov-17Networks and Communication Department28Sends many signals or “chips” per bit.Each sender uses a unique pattern of chips.May use multiple frequencies for spread spectrum communication.Common with wireless systems.
29. Any Question ?14-Nov-1729Networks and Communication Department