1. Data Communication and Networking 332 Hardware Components of Data Communications

2. Lecture Overview • Multiplexer • Multiplexing • FDM • TDM • WDM • Front-End Processor • Controllers

3. Multiplexer • A device that combines data from several devices into a single stream • Multiplexers are used in pairs (multiplexer and demultiplexer) • Increases efficiency, reduces cost • Idle time is reduced

4. Multiplexer Network using multiplexers

5. Multiplexer • Used in WANS, LANs, wireless networks • In WANs, used on point-to-point, multipoint lines • Connection multiplexer in LANs • Multiple radio signals combined on wireless networks

6. Multiplexer Corporate Network using multiplexers

7. Cascading Multiplexer • Connect communications lines to another multiplexer • Using several levels of multiplexers at several sites • Reduces costs

8. Cascading Multiplexer

9. Multiplexing • Many types of multiplexing techniques employed: • Frequency Division Multiplexing • Time Division Multiplexing • Synchronous Time Division Multiplexing • Statistical Time Division Multiplexing • Wave Division Multiplexing

10. Frequency Division Multiplexing • FDM is used with analog signals. • Used in television and radio transmission. • Bandwidth divided into narrow bandwidths

11. Frequency Division Multiplexing • How it works? • A multiplexer accepts analog signals from multiple sources, each of which has a specified bandwidth. • Guard bands (unused parts of the frequency range - It acts as a buffer between adjacent channels to avoid one channel’s data from crossing over into another channel) used to separate the signals. • The signals then are combined in to another, more complex signal with a much larger bandwidth. • The resulting signal is transmitted over some medium to its destination, where demultiplexer extracts and separates the individual components

12. Frequency Division Multiplexing Frequency Division Multiplexing

13. Time Division Multiplexing • TDM is used with digital signals. • Many input signals are combined and transmitted together. • The technique interleaves more than one individual digital signal into another channel by giving each original signal time a slot in the multiplexed channel. • TDM has split into two separate technologies; - synchronous time division multiplexing - statistical time division multiplexing

14. Synchronous Time Division Multiplexing • Each incoming source gets a turn to transmit, proceeding through the sources in round-robin fashion • The demultiplexor on the receiver end of the high speed link must disassemble the incoming bit stream and deliver each bit (or byte) to the appropriate destination • A precise order must be maintained so that the demultiplexor can disassemble and deliver the bits to the respective owners • Must maintaining synchronization between the receiver and transmitter • Must transmit empty slot and cannot take advantage of the empty slot.

15. Synchronous Time Division Multiplexing

16. Statistical Time Division Multiplexing • Transmit data only from active users i.e. no empty time slots • Multiplexer scan the buffers and create a variable-size frame depending on how many buffers contain data. • Frame is created that contains data and address of data to identify who sent the data and for whom it is intended • Examples - data entry systems, point of sale systems

17. Statistical Time Division Multiplexing • Advantage : • Does not need a line as high speed as synchronous time division multiplexing for transferring the same amount of data • Good for connecting a number of lower speed devices that do not transmit data on a continuous basis to a remote computer system • Disadvantage: • increased level of complexity.

18. Statistical Time Division Multiplexing

19. Wavelength Division Multiplexing • Used for analog and digital transmission over fiber optic cables • Optical signals from light sources consists of different wavelengths • The simultaneous transmission of these light sources over a single fiber-optic channel • Light sources of different wavelengths are combined by a WDM multiplexor before transmission • A WDM demultiplexor separates them and transmits them to their respective destination receivers

20. Wavelength Division Multiplexing Beneficial from cost and performance • it increases bandwidth without requiring the installation of additional fiber, (cost) • WDM consolidates data from separate channels onto a single line (performance)

21. Multiplexing Techniques

22. Front-End Processsor • FEP is a small-sized computer which interfaces to the host computer a number of networks, such as peripheral devices (terminals, disk units, printers and tape units) • Data is transferred between the host computer and the FEP using a high-speed parallel interface. • The FEP communicates with peripheral devices using slower serial interfaces. • The purpose is to off-load from the host computer the work of managing the peripheral devices, transmitting and receiving messages, packet assembly and disassembly, error detection and error correction

23. Front-End Processsor FEP in communications network

24. Controllers • Scaled-down version of an FEP • Handles up to 64 devices • Cluster controller • Specifically used with IBM servers • Remote controller • Located a distance from the server • Local controller • Located near the server

25. Controllers Controller in data communications network

26. QUESTIONS?