1. 6/10/2015 Unit-1 : Data Communications 1 CS 1302 Computer Networks — Unit - 1 — — Data Communications — Text Book Behrouz.A. Forouzan, “Data communication and Networking”, Tata McGrawHill, 2004

2. Overview of Data Communications and Networking 6/10/20152Unit-1 : Data Communications

3. Overview 6/10/20153Unit-1 : Data Communications

4. Introduction 6/10/20154Unit-1 : Data Communications

5. 1.1 Data Communication Components Data Representation Direction of Data Flow 6/10/20155Unit-1 : Data Communications

6. Figure 1.1 Five components of data communication 6/10/20156Unit-1 : Data Communications

7. Figure 1.2 Simplex 6/10/20157Unit-1 : Data Communications

8. Figure 1.3 Half-duplex 6/10/20158Unit-1 : Data Communications

9. Figure 1.4 Full-duplex 6/10/20159Unit-1 : Data Communications

10. 1.2 Networks Distributed Processing Network Criteria Physical Structures Categories of Networks 6/10/201510Unit-1 : Data Communications

11. Figure 1.5 Point-to-point connection 6/10/201511Unit-1 : Data Communications

12. Figure 1.6 Multipoint connection 6/10/201512Unit-1 : Data Communications

13. Figure 1.7 Categories of topology 6/10/201513Unit-1 : Data Communications

14. Figure 1.8 Fully connected mesh topology (for five devices) 6/10/201514Unit-1 : Data Communications

15. Figure 1.9 Star topology 6/10/201515Unit-1 : Data Communications

16. Figure 1.10 Bus topology 6/10/201516Unit-1 : Data Communications

17. Figure 1.11 Ring topology 6/10/201517Unit-1 : Data Communications

18. Figure 1.12 Categories of networks 6/10/201518Unit-1 : Data Communications

19. Figure 1.13 LAN 6/10/201519Unit-1 : Data Communications

20. Figure 1.13 LAN (Continued) 6/10/201520Unit-1 : Data Communications

21. Figure 1.14 MAN 6/10/201521Unit-1 : Data Communications

22. Figure 1.15 WAN 6/10/201522Unit-1 : Data Communications

23. 1.3 The Internet A Brief History The Internet Today 6/10/201523Unit-1 : Data Communications

24. Figure 1.16 Internet today 6/10/201524Unit-1 : Data Communications

25. 1.4 Protocols and Standards Protocols Standards Standards Organizations Internet Standards 6/10/201525Unit-1 : Data Communications

26. Network Models 6/10/201526Unit-1 : Data Communications

27. 2.1 Layered Tasks Sender, Receiver, and Carrier Hierarchy Services 6/10/201527Unit-1 : Data Communications

28. Figure 2.1 Sending a letter 6/10/201528Unit-1 : Data Communications

29. 2.2 Internet Model Peer-to-Peer Processes Functions of Layers Summary of Layers 6/10/201529Unit-1 : Data Communications

30. Figure 2.2 Internet layers 6/10/201530Unit-1 : Data Communications

31. Figure 2.3 Peer-to-peer processes 6/10/201531Unit-1 : Data Communications

32. Figure 2.4 An exchange using the Internet model 6/10/201532Unit-1 : Data Communications

33. Figure 2.5 Physical layer 6/10/201533Unit-1 : Data Communications

34. The physical layer is responsible for transmitting individual bits from one node to the next. Note: 6/10/201534Unit-1 : Data Communications

35. Figure 2.6 Data link layer 6/10/201535Unit-1 : Data Communications

36. The data link layer is responsible for transmitting frames from one node to the next. Note: 6/10/201536Unit-1 : Data Communications

37. Figure 2.7 Node-to-node delivery 6/10/201537Unit-1 : Data Communications

38. Example 1 In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection 6/10/201538Unit-1 : Data Communications

39. Figure 2.8 Example 1 6/10/201539Unit-1 : Data Communications

40. Figure 2.9 Network layer 6/10/201540Unit-1 : Data Communications

41. The network layer is responsible for the delivery of packets from the original source to the final destination. Note: 6/10/201541Unit-1 : Data Communications

42. Figure 2.10 Source-to-destination delivery 6/10/201542Unit-1 : Data Communications

43. Example 2 In Figure 2.11 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic. 6/10/201543Unit-1 : Data Communications

44. Figure 2.11 Example 2 6/10/201544Unit-1 : Data Communications

45. Figure 2.12 Transport layer 6/10/201545Unit-1 : Data Communications

46. The transport layer is responsible for delivery of a message from one process to another. Note: 6/10/201546Unit-1 : Data Communications

47. Figure 2.12 Reliable process-to-process delivery of a message 6/10/201547Unit-1 : Data Communications

48. Example 3 Figure 2.14 shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet. 6/10/201548Unit-1 : Data Communications

49. Figure 2.14 Example 3 6/10/201549Unit-1 : Data Communications

50. Figure 2.15 Application layer 6/10/201550Unit-1 : Data Communications

51. The application layer is responsible for providing services to the user. Note: 6/10/201551Unit-1 : Data Communications

52. Figure 2.16 Summary of duties 6/10/201552Unit-1 : Data Communications

53. 2.3 OSI Model A comparison 6/10/201553Unit-1 : Data Communications

54. Figure 2.17 OSI model 6/10/201554Unit-1 : Data Communications

55. Digital Transmission 6/10/201555Unit-1 : Data Communications

56. 4.1 Line Coding Some Characteristics Line Coding Schemes Some Other Schemes 6/10/201556Unit-1 : Data Communications

57. Figure 4.1 Line coding 6/10/201557Unit-1 : Data Communications

58. Figure 4.2 Signal level versus data level 6/10/201558Unit-1 : Data Communications

59. Figure 4.3 DC component 6/10/201559Unit-1 : Data Communications

60. Example 1 A signal has two data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ 10 -3 = 1000 pulses/s Bit Rate = Pulse Rate x log 2 L = 1000 x log 2 2 = 1000 bps 6/10/201560Unit-1 : Data Communications

61. Example 2 A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = = 1000 pulses/s Bit Rate = PulseRate x log 2 L = 1000 x log 2 4 = 2000 bps 6/10/201561Unit-1 : Data Communications

62. Figure 4.4 Lack of synchronization 6/10/201562Unit-1 : Data Communications

63. Example 3 In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent  1001 bits received  1 extra bps At 1 Mbps: 1,000,000 bits sent  1,001,000 bits received  1000 extra bps 6/10/201563Unit-1 : Data Communications

64. Figure 4.5 Line coding schemes 6/10/201564Unit-1 : Data Communications

65. Unipolar encoding uses only one voltage level. Note: 6/10/201565Unit-1 : Data Communications

66. Figure 4.6 Unipolar encoding 6/10/201566Unit-1 : Data Communications

67. Polar encoding uses two voltage levels (positive and negative). Note: 6/10/201567Unit-1 : Data Communications

68. Figure 4.7 Types of polar encoding 6/10/201568Unit-1 : Data Communications

69. In NRZ-L the level of the signal is dependent upon the state of the bit. Note: 6/10/201569Unit-1 : Data Communications

70. In NRZ-I the signal is inverted if a 1 is encountered. Note: 6/10/201570Unit-1 : Data Communications

71. Figure 4.8 NRZ-L and NRZ-I encoding 6/10/201571Unit-1 : Data Communications

72. Figure 4.9 RZ encoding 6/10/201572Unit-1 : Data Communications

73. A good encoded digital signal must contain a provision for synchronization. Note: 6/10/201573Unit-1 : Data Communications

74. Figure 4.10 Manchester encoding 6/10/201574Unit-1 : Data Communications

75. In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation. Note: 6/10/201575Unit-1 : Data Communications

76. Figure 4.11 Differential Manchester encoding 6/10/201576Unit-1 : Data Communications

77. In differential Manchester encoding, the transition at the middle of the bit is used only for synchronization. The bit representation is defined by the inversion or noninversion at the beginning of the bit. Note: 6/10/201577Unit-1 : Data Communications

78. In bipolar encoding, we use three levels: positive, zero, and negative. Note: 6/10/201578Unit-1 : Data Communications

79. Figure 4.12 Bipolar AMI encoding 6/10/201579Unit-1 : Data Communications

80. Figure 4.13 2B1Q 6/10/201580Unit-1 : Data Communications

81. Figure 4.14 MLT-3 signal 6/10/201581Unit-1 : Data Communications

82. 4.2 Block Coding Steps in Transformation Some Common Block Codes 6/10/201582Unit-1 : Data Communications

83. Figure 4.15 Block coding 6/10/201583Unit-1 : Data Communications

84. Figure 4.16 Substitution in block coding 6/10/201584Unit-1 : Data Communications

85. Table 4.1 4B/5B encoding DataCodeDataCode 000011110100010010 000101001100110011 001010100101010110 001110101101110111 010001010110011010 010101011110111011 011001110111011100 011101111111111101 6/10/201585Unit-1 : Data Communications

86. Table 4.1 4B/5B encoding (Continued) DataCode Q (Quiet)00000 I (Idle)11111 H (Halt)00100 J (start delimiter)11000 K (start delimiter)10001 T (end delimiter)01101 S (Set)11001 R (Reset)00111 6/10/201586Unit-1 : Data Communications

87. Figure 4.17 Example of 8B/6T encoding 6/10/201587Unit-1 : Data Communications

88. 4.3 Sampling Pulse Amplitude Modulation Pulse Code Modulation Sampling Rate: Nyquist Theorem How Many Bits per Sample? Bit Rate 6/10/201588Unit-1 : Data Communications

89. Figure 4.18 PAM 6/10/201589Unit-1 : Data Communications

90. Pulse amplitude modulation has some applications, but it is not used by itself in data communication. However, it is the first step in another very popular conversion method called pulse code modulation. Note: 6/10/201590Unit-1 : Data Communications

91. Figure 4.19 Quantized PAM signal 6/10/201591Unit-1 : Data Communications

92. Figure 4.20 Quantizing by using sign and magnitude 6/10/201592Unit-1 : Data Communications

93. Figure 4.21 PCM 6/10/201593Unit-1 : Data Communications

94. Figure 4.22 From analog signal to PCM digital code 6/10/201594Unit-1 : Data Communications

95. According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency. Note: 6/10/201595Unit-1 : Data Communications

96. Figure 4.23 Nyquist theorem 6/10/201596Unit-1 : Data Communications

97. Example 4 What sampling rate is needed for a signal with a bandwidth of 10,000 Hz (1000 to 11,000 Hz)? Solution The sampling rate must be twice the highest frequency in the signal: Sampling rate = 2 x (11,000) = 22,000 samples/s 6/10/201597Unit-1 : Data Communications

98. Example 5 A signal is sampled. Each sample requires at least 12 levels of precision (+0 to +5 and -0 to -5). How many bits should be sent for each sample? Solution We need 4 bits; 1 bit for the sign and 3 bits for the value. A 3-bit value can represent 2 3 = 8 levels (000 to 111), which is more than what we need. A 2-bit value is not enough since 2 2 = 4. A 4-bit value is too much because 2 4 = 16. 6/10/201598Unit-1 : Data Communications

99. Example 6 We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample? Solution The human voice normally contains frequencies from 0 to 4000 Hz. Sampling rate = 4000 x 2 = 8000 samples/s Bit rate = sampling rate x number of bits per sample = 8000 x 8 = 64,000 bps = 64 Kbps 6/10/201599Unit-1 : Data Communications

100. Note that we can always change a band-pass signal to a low-pass signal before sampling. In this case, the sampling rate is twice the bandwidth. Note: 6/10/2015100Unit-1 : Data Communications

101. 4.4 Transmission Mode Parallel Transmission Serial Transmission 6/10/2015101Unit-1 : Data Communications

102. Figure 4.24 Data transmission 6/10/2015102Unit-1 : Data Communications

103. Figure 4.25 Parallel transmission 6/10/2015103Unit-1 : Data Communications

104. Figure 4.26 Serial transmission 6/10/2015104Unit-1 : Data Communications

105. In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte. Note: 6/10/2015105Unit-1 : Data Communications

106. Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same. Note: 6/10/2015106Unit-1 : Data Communications

107. Figure 4.27 Asynchronous transmission 6/10/2015107Unit-1 : Data Communications

108. In synchronous transmission, we send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits. Note: 6/10/2015108Unit-1 : Data Communications

109. Figure 4.28 Synchronous transmission 6/10/2015109Unit-1 : Data Communications

110. 5.2 Telephone Modems Modem Standards 6/10/2015110Unit-1 : Data Communications

111. A telephone line has a bandwidth of almost 2400 Hz for data transmission. Note: 6/10/2015111Unit-1 : Data Communications

112. Figure 5.18 Telephone line bandwidth 6/10/2015112Unit-1 : Data Communications

113. Modem stands for modulator/demodulator. Note: 6/10/2015113Unit-1 : Data Communications

114. Figure 5.19 Modulation/demodulation 6/10/2015114Unit-1 : Data Communications

115. Figure 5.20 The V.32 constellation and bandwidth 6/10/2015115Unit-1 : Data Communications

116. Figure 5.21 The V.32bis constellation and bandwidth 6/10/2015116Unit-1 : Data Communications

117. Figure 5.22 Traditional modems 6/10/2015117Unit-1 : Data Communications

118. Figure 5.23 56K modems 6/10/2015118Unit-1 : Data Communications

119. Transmission Media 6/10/2015119Unit-1 : Data Communications

120. Figure 7.1 Transmission medium and physical layer 6/10/2015120Unit-1 : Data Communications

121. Figure 7.2 Classes of transmission media 6/10/2015121Unit-1 : Data Communications

122. 7.1 Guided Media Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable 6/10/2015122Unit-1 : Data Communications

123. Figure 7.3 Twisted-pair cable 6/10/2015123Unit-1 : Data Communications

124. Figure 7.4 UTP and STP 6/10/2015124Unit-1 : Data Communications

125. Table 7.1 Categories of unshielded twisted-pair cables CategoryBandwidthData RateDigital/AnalogUse 1very low< 100 kbpsAnalogTelephone 2 < 2 MHz2 MbpsAnalog/digitalT-1 lines 3 16 MHz 10 MbpsDigitalLANs 4 20 MHz 20 MbpsDigitalLANs 5 100 MHz 100 MbpsDigitalLANs 6 (draft) 200 MHz 200 MbpsDigitalLANs 7 (draft) 600 MHz 600 MbpsDigitalLANs 6/10/2015125Unit-1 : Data Communications

126. Figure 7.5 UTP connector 6/10/2015126Unit-1 : Data Communications

127. Figure 7.6 UTP performance 6/10/2015127Unit-1 : Data Communications

128. Figure 7.7 Coaxial cable 6/10/2015128Unit-1 : Data Communications

129. Table 7.2 Categories of coaxial cables CategoryImpedanceUse RG-59 75  Cable TV RG-58 50  Thin Ethernet RG-11 50  Thick Ethernet 6/10/2015129Unit-1 : Data Communications

130. Figure 7.8 BNC connectors 6/10/2015130Unit-1 : Data Communications

131. Figure 7.9 Coaxial cable performance 6/10/2015131Unit-1 : Data Communications

132. Figure 7.10 Bending of light ray 6/10/2015132Unit-1 : Data Communications

133. Figure 7.11 Optical fiber 6/10/2015133Unit-1 : Data Communications

134. Figure 7.12 Propagation modes 6/10/2015134Unit-1 : Data Communications

135. Figure 7.13 Modes 6/10/2015135Unit-1 : Data Communications

136. Table 7.3 Fiber types TypeCoreCladdingMode 50/125 50125Multimode, graded-index 62.5/125 62.5125Multimode, graded-index 100/125100125Multimode, graded-index 7/125 7125Single-mode 6/10/2015136Unit-1 : Data Communications

137. Figure 7.14 Fiber construction 6/10/2015137Unit-1 : Data Communications

138. Figure 7.15 Fiber-optic cable connectors 6/10/2015138Unit-1 : Data Communications

139. Figure 7.16 Optical fiber performance 6/10/2015139Unit-1 : Data Communications

140. 7.2 Unguided Media: Wireless Radio Waves Microwaves Infrared 6/10/2015140Unit-1 : Data Communications

141. Figure 7.17 Electromagnetic spectrum for wireless communication 6/10/2015141Unit-1 : Data Communications

142. Figure 7.18 Propagation methods 6/10/2015142Unit-1 : Data Communications

143. Table 7.4 Bands BandRangePropagationApplication VLF3–30 KHzGroundLong-range radio navigation LF30–300 KHzGround Radio beacons and navigational locators MF300 KHz–3 MHzSkyAM radio HF3–30 MHzSky Citizens band (CB), ship/aircraft communication VHF30–300 MHz Sky and line-of-sight VHF TV, FM radio UHF300 MHz–3 GHzLine-of-sight UHF TV, cellular phones, paging, satellite SHF3–30 GHzLine-of-sightSatellite communication EHF30–300 GHzLine-of-sightLong-range radio navigation 6/10/2015143Unit-1 : Data Communications

144. Figure 7.19 Wireless transmission waves 6/10/2015144Unit-1 : Data Communications

145. Figure 7.20 Omnidirectional antennas 6/10/2015145Unit-1 : Data Communications

146. Radio waves are used for multicast communications, such as radio and television, and paging systems. Note: 6/10/2015146Unit-1 : Data Communications

147. Figure 7.21 Unidirectional antennas 6/10/2015147Unit-1 : Data Communications

148. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Note: 6/10/2015148Unit-1 : Data Communications

149. Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation. Note: 6/10/2015149Unit-1 : Data Communications