Computer application in management for third year

Used for mgt

1. UNIT 4 DATA COMMUNICATIONS Computer application in management

2. Unit Outline 4.1 Introduction 4 .2 Basic Elements of a Communication System 4.2.1 Data Transmission Modes 4.2.2 Transmission Basics 4.3 Types of Data Transmission Media 4.3.1 Bounded Media 4.3.2 Unbounded Media 4 .4 Modulation Techniques 4.4.1 Modems 4.4.2 Analog versus Digital Transmission 4.5 Multiplexing 4.5.1 Time Division Multiplexing (TDM) 4.5.2 Frequency Division Multiplexing (FDM)

3. 4.1 Introduction Data Communications concerns the transmission of digital messages to devices external to the message source.

4. 4.2 Basic Elements of a Communication System Communication is the process of transferring messages and data from one point to another.

5. The three basic elements of any communication process are : 1) A sender (source) which creates the message to be transmitted. 2 ) A medium which carries the message. 3 ) A receiver (Sink) which receives the message.

6. For example when we speak to our friend over telephone we are sender , the telephone line through which our voice is transmitted is a medium and our friend is a receiver . This is a simple example of voice communication. The same concept holds for the data communication also.

7. 4 .2.1 Data Transmission Modes Data transmission , whether analog or digital , may also be characterized by the direction in which the signals travel over the media.

8. Simplex : Data is sent from sender to receiver. Signals may travel in only one direction. Simplex is sometimes called one-way , or unidirectional communication.

9. Real-life examples of full communication include : Radio broadcasting Television broadcasting Computer to print Monitor output Mouse / keyboard to computer Loud speaker

10. Advantage of simplex mode simplex mode is the easiest and mos reliable mode of communication Is cost-effective mode No need for coordination b/n the transmitting and receiving devices which simplifies the communication

11. Disadvantage of simplex mode Only one way communication is possible. There is no way to verify if the transmitted data has been received correctly. Simplex mode is not suitable for application that require bidirectional communication

12. 2. Half Duplex Data can transmit both ways, but not simultaneously Signals may travel in both directions over a medium but in only one direction at a time. Half-duplex systems contain only one channel for communication, and that channel must be shared for multiple nodes to exchange information.

13. Real-life examples of full communication include : A two-way radio that has a push-to-talk button Browsing the internet(requests and responses) Universal Serial Bus (USB)

14. Advantage of Half-duplex mode Half-duplex mode allows for bidirectional communication, which is useful in situations where devices need to send and receive data. it is a more efficient mode of communication than simplex mode, the channel can be used for both transmission and reception. Half-duplex mode is less expensive than full-duplex mode, as it only requires one communication channel.

15. Disadvantage of Half-duplex mode Half-duplex mode is less reliable than full-duplex mode, as both devices cannot transmit at the same time. There is delay b/n transmission and reception, which can cause problems in some application. There is need for coordination b/n the transmitting and receiving devices, which can complicate the communication process.

16. 3. Full-Duplex Signals are free to travel in both directions over a medium simultaneously . Data can transmit both ways at the same time. Full duplex may also be called bi-directional transmission or sometimes, simply duplex.

17. Real-life examples of full communication include : Video calls/video conferencing Audio calls Live chats

18. Advantage of Full-duplex mode Full-duplex mode allows for simultaneous bidirectional communication, which is ideal for real-time application such as video conferencing or online gaming. It is the most efficient mode of communication, as both devices can transmit and receive data simultaneously. Full-duplex mode provides a high level of reliability and accuracy, as there is no need for error correction mechanisms .

19. Disadvantage of Full-duplex mode Full-duplex mode is the most expensive mode, as it requires two communication channels. It is more complex than simplex and half-duplex mode, as it requires two physically separate transmission paths or a division of channel capacity. Full-duplex mode may not suitable for all applications, as it requires a high level of bandwidth and may not be necessary for some type of communication.

20. A channel is a distinct communication path between two or more nodes.

21. 4 .2.2 Transmission Basics In data networking, the term transmission has two meanings . First , it can refer to the process of issuing data signals on a medium . Second, it can also refer to the progress of data signals over a medium from one point to another .

22. Analog and Digital Signalling One important characteristic of data transmission is the type of signalling involved . On a data network, information can be transmitted via one of two signalling methods:

23. i . Analog ii . Digital

24. Both types of signals are generated by electrical current, the pressure of which is measured in volts. The strength of an electrical signal is directly proportional to its voltage.

25. The essential difference between analog and digital signals is the way voltage creates and sustains the signal.

26. 1. Analog Signaling In analog signals, voltage varies continuously. In digital signals, voltage turns off and on repeatedly, pulsing from zero voltage to a specific positive voltage. An analog signal’s voltage appears as a continuous wave when graphed over time, because voltage is varied and imprecise in analog signals, Analog transmission is more susceptible/ disposaed to transmission flaws such as noise than digital signals.

27. 2. Digital Signaling Unlike analog signals where there is a smooth curve, digital signals jump directly to the next value. When digital signals can exist in only one of two values, they go directly to the next value, typically changing between 0 and 1.

28. The jump from one value to another is known as a transition . Data rate is measured in bits per second ( bps ).

29. Data rate: This is the rate, in bits per second (bps), at which data can be communicated. Bandwidth : This is the maximum bandwidth of the transmitted signal as constrained by the nature of the transmission medium or transmission channel, expressed in cycles per second, or hertz (Hz).

30. Noise : The average level of noise over the communications path. Error rate : The rate at which errors occur, where an error is the reception of a 1 when a was transmitted or the reception of a when a 1 was transmitted.

31. 4.3 TYPES OF DATA TRANSMISSION MEDIA Data Transmission Media is divided into two types 1 ) Bounded Media 2 ) Unbounded Media

32. 4.3.1 Bounded Media Bounded Media is also known as guided media . Bounded media are great for LANs because they offer high speed, good security, and low cost.

33. Three common types of bounded media are: Coaxial b ) Twisted pair c ) Fiber optic

34. a) Coaxial Cable Coaxial cable consists of a central copper core surrounded by an insulator , a braided metal shielding, called braiding , and an outer cover, and called the sheath or jacket .

35. Because of its insulation and protective braiding, coaxial cable has a high resistance to interference from noise . Coaxial cable is also less desirable than twisted-pair because it supports lower throughput.

36. b) Twisted-Pair Cable The most popular network cabling right now is twisted pair. It is lightweight, easy to install, inexpensive, and supports many different types of networks. It can also supports speeds of up to 100Mbps.

37. Twisted-pair cabling is made up of pairs of solid or stranded copper twisted around each other. The twists are done to reduce the vulnerability to EMI and cross talk. The number of pairs in the cable depends on the type. The copper core of the cable is usually 22-AWG or 24-AWG, as measured on the American Wire Gauge standard.

38. Twisted-pair (TP) cable is similar to telephone wiring and consists of color-coded pairs of insulated copper wires, each with a diameter of 0.4 to 0.8 mm, or 22-24 AWG (American Wire Gauge) standard copper wires.

39. C. Fiber-Optic Cable Fiber-optic cable, or simply fiber , contains one or several glass fibers at its center, or core. Data are transmitted via pulsing light sent from a laser or light-emitting diode (LED) through the central fibers . Surrounding the fibers is a layer of glass called cladding.

40. 4.3.2 Unbounded Media Unbounded, or wireless, media does not use any physical connectors between the two devices communicating. Usually the transmission is sent through the atmosphere, but sometimes it can be just across a room. Wireless media is used when a physical obstruction or distance blocks the use of normal cable media.

41. Following are the types of unbounded media : 1. Radio Waves i . Short-wave ii . Very-high frequency (VHF ) television and radio iii. Ultra-high frequency (UHF) television and radio Micro waves 2 . Microwaves i . Terrestrial Microwaves ii. Satellite Microwaves 3. Infrared i . Point-to-point ii . Broadcast

42. 1. Radio Waves Radio waves have frequencies between 10 KHz and 1GHz .

43. Radio waves include the following types : i . Short-wave ii. Very-high frequency ( VHF) television and radio iii. Ultra-high frequency (UHF) television and radio Micro waves

44. Most radio frequencies in the US and Canada are regulated. To gain permission to use a regulated frequency can take a long time and a large amount of money. The good news is that there are some frequencies that are not regulated and anyone can use.

45. The problem with unregulated frequencies is that they can get saturated. To ease this, there have been limits set on the amount of power that devices can broadcast in these frequencies.

46. 2. Microwaves Microwaves travel at higher frequencies than radio waves and provide better throughput as a wireless network media. Microwave transmissions require the sender to be within sight of the receiver. These systems use licensed frequencies, which makes them more costly than radio wave systems.

47. Microwaves are utilized on the following two types of communication systems : i . Terrestrial Microwaves Terrestrial microwave transmissions are used to transmit wireless signals across a few miles. ii. Satellite Microwaves Satellite microwave transmissions are used to transmit signals throughout the world.

48. 3. Infrared Infrared frequencies are just below visible light. These high frequencies allow high-speed data transmissions.

49. These transmissions fall into the following two categories : i . Point-to-point Infrared Point-to-point infrared transmissions utilize highly focused beams to transfer signals directly between two systems.

50. ii. Broadcast infrared Broadcast infrared transmissions use a spread signal, one broadcast in all directions, instead of a direct beam.