[CS61C FA20] Lecture 31.5 - I/O: Networking — Transcript

Full transcript

1. 0:00[Music]
2. 0:10hello
3. 0:11and welcome back to the wrap-up of the
4. 0:14module
5. 0:14that has been dealing with operating
6. 0:17systems
7. 0:18virtual memory and io devices other
8. 0:21devices
9. 0:22that we have talked about so far
10. 0:25generally deal with the devices that are
11. 0:28within
12. 0:28one machine one computer disks
13. 0:32keyboards mice displays and so on
14. 0:38do we do something different to connect
15. 0:41our computer to our computers
16. 0:43through networking well it's all done on
17. 0:47the same principles
18. 0:48so let's just quickly recap what do we
19. 0:50do
20. 0:51with the networking so
21. 0:54the idea of networking started
22. 0:56originally to share
23. 0:58devices between the computers like
24. 1:00printers in the office
25. 1:03then people started getting
26. 1:08much more interest in moving files
27. 1:11between computers
28. 1:12instead of just copying them on a device
29. 1:14that we used to have that was called the
30. 1:16floppy disk
31. 1:18um you could just send them directly to
32. 1:20another
33. 1:22device by using ftp or file transfer
34. 1:24protocol
35. 1:26then they figured out that it don't
36. 1:29have to be like typed up files about
37. 1:32you know some documents or a
38. 1:34presentation or something like that
39. 1:36people started using email
40. 1:39then we started communicating between
41. 1:44the networks of computers
42. 1:46so we ended up with file sharing
43. 1:49networks world wide web
44. 1:51and many many many other things
45. 1:55that run today's world how did the
46. 1:58internet uh
47. 1:59start about well um it started with
48. 2:02ideas a long time ago around 1962.
49. 2:07um look like they're all also known as
50. 2:10lick while he was at
51. 2:14dod's arpa which is nowadays darpa
52. 2:18wrote a memo describing a desire to
53. 2:20connect computers
54. 2:22and he was targeting actually research
55. 2:24network that would be connecting
56. 2:26computers at stanford berkeley and ucla
57. 2:30in 1969 so-called arpanet
58. 2:35debuted and connected computers at ucla
59. 2:39sri staff research institute
60. 2:42utah and uc santa barbara not berkeley
61. 2:47then robert khan and vincerp invented
62. 2:51the
63. 2:51tcp which is now part of
64. 2:55the internet practical suite this is a
65. 2:58way
66. 2:59how the computers talk to each other
67. 3:04internet from day one this
68. 3:07desire to connect computers was very
69. 3:10appealing
70. 3:11and internet has been growing
71. 3:13exponentially
72. 3:14from then until now and into a for
73. 3:18foreseeable future worldwide web
74. 3:22came around when i was in college
75. 3:2589 and it was clunky early on it was
76. 3:29uh implemented by term tim berners-lee
77. 3:32uh started at cern
78. 3:36and then i think tim moved over to
79. 3:40mit um it
80. 3:44was called the system of inter
81. 3:46interlinked hypertext documents
82. 3:48on the internet um the idea
83. 3:51originates uh early on to whenever bush
84. 3:54um
85. 3:55one of the really big computing pioneers
86. 3:59that called envisioned a system like
87. 4:01that but did not
88. 4:02implement it
89. 4:06well um timber nursery implemented
90. 4:10the http
91. 4:13and server using the internet
92. 4:17it didn't take very long for the whole
93. 4:19world to explode
94. 4:21we witnessed the dot com boom
95. 4:24and the bust after that that followed in
96. 4:272001
97. 4:28but everything recovered and we have
98. 4:30access everywhere
99. 4:33so what is behind the protocol there
100. 4:37generally we send packets of data
101. 4:41these packets of data are produced by
102. 4:44software
103. 4:46the software will
104. 4:49you know the software application will
105. 4:52copy
106. 4:52the data to the os buffer os will
107. 4:55calculate some kind of a checksum such
108. 4:57that if there are errors during
109. 4:58transmission because when
110. 4:59data go on a far you know far or
111. 5:03long trip some bits may get corrupted
112. 5:06uh start a timer and then os sends the
113. 5:09data to a network interface a hardware
114. 5:11network
115. 5:12interface and says start
116. 5:16the data is packaged in a particular way
117. 5:18as it's shown here
118. 5:21that has its address of the destination
119. 5:25of the source the link because some of
120. 5:27these packets may be variable linked
121. 5:29has some acknowledgement info and the
122. 5:32payload which may be
123. 5:34comments addresses or data and finally
124. 5:36there's a
125. 5:37has a trailer in the form of a checksum
126. 5:40india
127. 5:40checksum in the end now
128. 5:43um on the receive side
129. 5:47the data will show up in another network
130. 5:49interface
131. 5:51you know that's a special card um and
132. 5:55will be transferred to the
133. 5:56operating system buffer i think you're
134. 5:58guessing what how would would end up
135. 6:00being
136. 6:01transferred to the uh os buffer or as
137. 6:03we'll
138. 6:04check if the checksum is correct if it
139. 6:06matches
140. 6:07if it is okay it will send the
141. 6:09acknowledgement back
142. 6:10to the sender if
143. 6:14it is not okay then it will delete the
144. 6:16message
145. 6:18and um
146. 6:22the sender is going to send it again
147. 6:24center is also going to send it again
148. 6:26if the if it does not receive an
149. 6:28acknowledgement
150. 6:30after the timer expires
151. 6:33if everything is okay the message has
152. 6:35been received
153. 6:36and the os will copy it to the user
154. 6:39space
155. 6:39and signal supplication to continue and
156. 6:42i think we all know
157. 6:43the mechanism mechanisms how to do that
158. 6:48what do we need in order to implement
159. 6:49all this wonderful thing
160. 6:51well we know everything we traditionally
161. 6:54it is done
162. 6:54using a network interface card um it's a
163. 6:57card
164. 6:58like this one that you will find
165. 6:59nowadays in servers
166. 7:02if it is a laptop it really shrunk to
167. 7:04something
168. 7:05that is just a chip on a board and you
169. 7:08will generally find the wired or
170. 7:09wireless interfaces
171. 7:12how is the data transferred in some
172. 7:13older cards it was done by using
173. 7:16programmed i o in eurocards it's a dma
174. 7:21so the dma is the mechanism
175. 7:24to transfer data that is going to go
176. 7:28on a long wedge over the internet from
177. 7:32the main memory in the same way when it
178. 7:34arrives
179. 7:35to the to the destination its network
180. 7:37interface card
181. 7:38is going to use dma to transfer it back
182. 7:41to the memory and that's it
183. 7:45we have concluded this module we have
184. 7:48actually
185. 7:49done something again another big step
186. 7:52we have figured out how computers work i
187. 7:54mean i know that
188. 7:55we all know how computers work but we
189. 7:58now
190. 7:59really know how they work we also
191. 8:02figured out
192. 8:02how does the os work and how can we
193. 8:06interact with it
194. 8:07we do have to take more classes to
195. 8:09actually write an operating system
196. 8:11but we may not need to do that
197. 8:15we may be happy with just knowing how to
198. 8:18interact it and pick some other classes
199. 8:20the tourist classes are cool
200. 8:23we also in the process built a virtual
201. 8:25memory system and figured out how
202. 8:27various kinds of physical devices work
203. 8:30and why do we have such
204. 8:32huge differences in
205. 8:35speeds and affordability of different
206. 8:37classes of memory
207. 8:39so we get physical reasons why we had to
208. 8:42build this big memory here hierarchy
209. 8:46so that we can build this illusion of
210. 8:50infinitely fast and infinitely big
211. 8:53memory
212. 8:54system and in the end we figured out
213. 8:57how to attach peripherals to perform
214. 9:01input and output and the same mechanism
215. 9:04is used for
216. 9:06connecting disks
217. 9:09and ethernet cards to connect
218. 9:12to the rest of the world
219. 9:15that's it for this whole module
220. 9:19we'll see you in the parallelism module
221. 9:21after a longer break