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1. 0:00EP 1100 data communication and computer
2. 0:04networks some illustration in this
3. 0:06material are collected from the book by
4. 0:08foron data Communications and networking
5. 0:10published by
6. 0:12mcrill in this next part we're going to
7. 0:14talk about transmission and data
8. 0:16communication the overview is the
9. 0:18following first I go through the basics
10. 0:20of data communication then we look at
11. 0:22transmission media both guided and
12. 0:24unguided
13. 0:26media then we look at the transmission
14. 0:29capacity that you get from a
15. 0:30transmission medium the attenuation that
16. 0:33makes the signal weaker as it propagates
17. 0:35the Distortion that the signal is
18. 0:36subjected to and the limitations
19. 0:39ultimately that are placed on the data
20. 0:41rate then we look at actual ways of um
21. 0:44transmitting data over a medium by
22. 0:46modulation and line coding we look at
23. 0:48the framing of data and
24. 0:51synchronization and multiplexing of
25. 0:53multiple data streams and give some
26. 0:55examples of a Time Division multiplexing
27. 0:58and a synchronous digital subscriber
28. 1:00Loops the basics of data communication
29. 1:04relies on propagation of electromagnetic
30. 1:07signals we take the signals and we form
31. 1:10them into well- defined waveforms the
32. 1:12example below shows a sinusoidal wave
33. 1:15that has two amplitudes a lower
34. 1:16amplitude and a higher amplitude we can
35. 1:19let these two amplitudes represent the
36. 1:21bit value so in this case as you see a
37. 1:24low amplitude is a zero and high
38. 1:26amplitude represents bit value one then
39. 1:29we send the dat data by modulating the
40. 1:31waveform by the selected data it doesn't
41. 1:34have to be assigned a Sol we could have
42. 1:36a direct current that we chop by
43. 1:39switching it on and off and here no
44. 1:42signal means zero and Signal means one
45. 1:45this signal propagates through medium or
46. 1:47through vacuum
47. 1:49even the receiver detects the waveform
48. 1:53and Maps the waveform back to data bits
49. 1:55it will also have to handle errors that
50. 1:57might occur in the transmission
51. 2:00transmission media this simple schematic
52. 2:03shows a transmission medium going from a
53. 2:05transmitter to receiver it illustrates a
54. 2:08wave guide so that the electromagnetic
55. 2:10wave is contained into one guide that
56. 2:13leads it forward towards the
57. 2:16receiver here we also illustrate that
58. 2:18there could be intermediary equipment in
59. 2:20the medium for amplifying the signal or
60. 2:23generating the signal to guided media of
61. 2:26a transmission of electrical and
62. 2:27electromagnetic signals we look at TW
63. 2:30Pair cable and Co axle cable and also
64. 2:32for optical single where we look at the
65. 2:34single mode and multi mode fiber then we
66. 2:37have unguided media so free space
67. 2:38communication with electromagnetic waves
68. 2:41that carried in the air or in vacuum
69. 2:43such as radio waves microwaves and
70. 2:46infrared
71. 2:48waves I'm now going to show you some
72. 2:50guided media often when we talk about
73. 2:52wave guides we call them wires or cables
74. 2:55so here we have twisted pair cables
75. 2:57coaxial cables and Optical fibers a
76. 3:00twisted per cable is a very simple cable
77. 3:02it has two conductors that are insulated
78. 3:05and the cables are twisted together to
79. 3:07minimize the external disturbances that
80. 3:09can be generated in in the cable and
81. 3:12disturb the signals that's being
82. 3:16transmitted twisted pair cables often
83. 3:18have several pairs bundled together
84. 3:21often we have a connector such as the HP
85. 3:24HC connector often referred to as
86. 3:27rg45 and it's often installed in
87. 3:29building buildings it's a cable that's
88. 3:32cheap and simple to install and to put
89. 3:34contacts
90. 3:35on there are shielded versions and
91. 3:37unshielded version the unshielded
92. 3:39version is most common and it's called
93. 3:41UTP the shielding protects from external
94. 3:44noise and cross talk but it's bulkier
95. 3:46and more
96. 3:47expensive here's a table of different
97. 3:49categories of unshielded twisted pair
98. 3:51cables the most common today is the 5e
99. 3:54and the six categories which are used
100. 3:57for local area networks and can support
101. 3:59bit rate it's up to a gbit per
102. 4:01second coaxil cable has a different
103. 4:04construction it has an inner conductor
104. 4:07an insulator an outer conductor an
105. 4:10insulator and then a plastic cover and
106. 4:13it has a higher band with a twisted pair
107. 4:16cable optical fiber for light signals
108. 4:20consists of a core of silica glass or
109. 4:22plastic and then it has a clading with
110. 4:25lower index of refraction so that it
111. 4:27mirrors the light signal in the core
112. 4:30this reflection depends on the angle of
113. 4:32incidence into the fiber when the sender
114. 4:34sends light in the core acts like a
115. 4:37cylindrical mirror so the signal can
116. 4:40propagate by Reflections on the
117. 4:43interface between the core and the
118. 4:45cladding the light sources are light
119. 4:47emitting diodes or liys
120. 4:49diodes here I illustrate two forms of
121. 4:52fiber the single mode fiber and the
122. 4:54multim mood fiber we can take the multim
123. 4:56mood fiber first the core is so broad
124. 4:59that that are different angles of the
125. 5:01light that comes in that get reflected
126. 5:04and as I try to illustrate here with the
127. 5:06arrows you can see that the different
128. 5:08angles result in different Paths of
129. 5:11propagation through the fiber light path
130. 5:14that bounces the most goes the longest
131. 5:16distance through the fiber if you send
132. 5:18in a pulse to multimode fiber it will
133. 5:21propagate along all the different paths
134. 5:24once it received on the other side all
135. 5:26the different versions of the pulse will
136. 5:29be super imposed and the pulse will not
137. 5:31be as sharp any longer since the
138. 5:33distances that the pulse copies have
139. 5:35traveled are differently
140. 5:37long in a single mod f the core is so
141. 5:41small that there's only a single angle
142. 5:44that will lead to reflection and
143. 5:46propagates through the fiber the quality
144. 5:48of fiber is very high for transmission
145. 5:51we measure the loss in debels per
146. 5:53kilometer of fiber and typical values
147. 5:55are 0.3 DB per
148. 5:58kilometer they're both advantages and
149. 6:01disadvantages with optical fiber the
150. 6:03advantage is that it's very high
151. 6:05bandwidth has low attenuation as
152. 6:07mentioned there's no cross talk so
153. 6:09because photons don't interfere with one
154. 6:12another they're not sensitive to
155. 6:14electromagnetic noise and the cable has
156. 6:16a low weight per
157. 6:18meter disadvantages relate to the
158. 6:20installation to pull the cable is is not
159. 6:23so simple it's difficult to bend it
160. 6:25sharply because if you bend it too
161. 6:26sharply the light will not Mir get
162. 6:30mirrored inside the the fiber and you
163. 6:32will have a high loss of the
164. 6:34signal connecting cable segments
165. 6:36together requires wielding and adding
166. 6:39connectors is is a complicated
167. 6:41mechanical procedure especially for
168. 6:43single mode fiber maintenance and repair
169. 6:46is also more costly than for a twisted
170. 6:48pair or a quaal
171. 6:52cable signals can also propagate in free
172. 6:57space here I show different ways of
173. 6:59propagation if you take low frequency
174. 7:02radio signals they actually follow the
175. 7:04surface of of the earth so you can reach
176. 7:07long distances Beyond the
177. 7:09Horizon in in Sky propagation you can
178. 7:13bounce radio beans of the ionosphere and
179. 7:15then at higher frequencies above 30 mahz
180. 7:19you have to have a direct path for the
181. 7:22signals to propagate between the cender
182. 7:23and the receiver we talk about radio
183. 7:26waves that are used for a television
184. 7:28broadcast these are signals with
185. 7:30frequencies up to a gahz pass through
186. 7:33most obstacles like walls and vegetation
187. 7:36the transmission is terrestrial or use a
188. 7:39satellite often with omnidirectional
189. 7:41antennas to reach wide areas and often
190. 7:44sent from high towers for line of sight
191. 7:47propagation to the receivers when you go
192. 7:49up in frequency you come to a range
193. 7:51that's called
194. 7:52microwaves often considered being from
195. 7:55about 1 GHz up to 300
196. 7:58GHz now the signal is attenuated more by
197. 8:01obstacles and water and other reasons so
198. 8:05the signals start be more like light
199. 8:07signals this range is used for Celler
200. 8:10phones for WiFi and for satellite
201. 8:12networks it requires a li line of site
202. 8:16propagation you can use unidirectional
203. 8:19antennas to create Point to-point
204. 8:20microwave links or omnidirectional
205. 8:23antennas for mobile and broadcast
206. 8:27communication infrared light signals
207. 8:30have frequencies from 300 GHz to 400
208. 8:33terahz so they belong to the non-visible
209. 8:35part of the light spectrum it's
210. 8:37basically heat
211. 8:39radiation here again we have line of
212. 8:41sight propagation but Reflections can be
213. 8:43used to bypass
214. 8:46obstacles there's interference to this
215. 8:48from um sun rays since it's heat
216. 8:51radiation and this communication often
217. 8:53used for short distances for instance
218. 8:55for remote controls here is an
219. 8:58illustration of the bandw for different
220. 9:00media you see the twisted pair going up
221. 9:03to about 100 mahz coaxil Cable going up
222. 9:06to gigahertz you see the position of the
223. 9:09broadcast services like AM FM radio and
224. 9:14television the microwave range which
225. 9:16used for radar microwave ovens and and
226. 9:20uh microwave communication and then the
227. 9:22infrared and and eventually visible
228. 9:24light where the optical fiber is
229. 9:28used