Free CCNA | OSI Model & TCP/IP Suite | Day 3 | CCNA 200-301 Complete Course — Transcript

Full transcript

1. 0:01Welcome to my complete CCNA, Cisco Certified Network Associate course.
2. 0:06This is Jeremy’s IT Lab.
3. 0:09This course aims to be a complete course for the CCNA, including everything you need to
4. 0:14pass the exam, all 100% free.
5. 0:18Stay tuned till the end of the video for the quiz to test your knowledge of the material
6. 0:22in this video.
7. 0:23Also, remember to download and use the Anki flashcards with the link in the description.
8. 0:28Let’s get started.
9. 0:32This third lesson is about two networking models.
10. 0:35The first is the OSI Model, and the second is the TCP/IP suite.
11. 0:43Note that the TCP/IP suite is a networking model, too, but it’s usually referred to
12. 0:48as the TCP/IP suite, or just TCP/IP.
13. 0:53Unless you’re familiar with networking, you probably haven’t heard of the OSI model.
14. 0:58However, you probably have heard of TCP/IP, or at least the second part of that name,
15. 1:04IP, the Internet Protocol, for example you’ve probably heard of an IP address before.
16. 1:10So, what is a networking model?
17. 1:14Well, networking models categorize and provide a structure for networking protocols and standards.
18. 1:21Do you remember what a networking protocol is?
19. 1:24I talked a bit about Ethernet, and various standards for copper and fiber-optic cables
20. 1:29in the Day 2 video.
21. 1:31That’s an example of a protocol.
22. 1:34A networking protocol is a set of rules defining how network devices and software should work,
23. 1:41including how they should work together.
24. 1:43By the way, protocols refer to logical rules about how devices should communicate, not
25. 1:48physical standards.
26. 1:50So, you could visualize it like this.
27. 1:53This is a networking model, and it categorizes and provides a structure for various networking
28. 1:58protocols
29. 1:59like these.
30. 2:01The different colors represent different categories of protocols and standards.
31. 2:06These protocols and standards could define something like the structure and usage of
32. 2:10IP addresses, or maybe physical details like electrical voltage used on copper cables when
33. 2:16transmitting data.
34. 2:17Let’s talk about the OSI model first, and then we’ll look at the TCP/IP suite after.
35. 2:24So, what if there were no standard networking models and protocols?
36. 2:29Here’s a few Dell PCs and a few iMacs.
37. 2:35If Dell and Apple each made their own networking model, each with their own set of networking
38. 2:40protocols, these Dells would be able to communicate with each other, and these iMacs would be able
39. 2:45to communicate with each other, but because the Dells and iMacs would speak a different language
40. 2:50than each other, with a different set of rules about how to communicate, the Dells wouldn’t
41. 2:55be able to communicate with the imacs.
42. 2:58This is obviously a problem in modern networks, such as the Internet, where we expect devices
43. 3:03from various makers in various countries to be able to communicate with each other.
44. 3:09The OSI model is one attempt at standardizing network communications.
45. 3:14Although it isn’t actually in use today, it has had a big impact on how network engineers
46. 3:18think about networking, and we still refer to it today.
47. 3:23OSI stands for ‘open systems interconnection’ model.
48. 3:28Open, means that it is an open standard, not a proprietary model developed and used by
49. 3:33an individual company.
50. 3:36It is a conceptual model that categorizes and standardizes the different functions in
51. 3:40a network.
52. 3:42It was created by the international organization for standardization, the ISO, in the late
53. 3:481970s and early 1980s.
54. 3:52Network functions are divided into 7 layers.
55. 3:55For example, look at the bottom Layer, layer 1.
56. 3:58It is the physical layer.
57. 4:00The standards for cables and interfaces we learned about in the Day 2 video all fit into
58. 4:05the physical layer of the OSI model, but there are 6 more layers on top of that to make the
59. 4:11network operate properly.
60. 4:13Let’s examine each layer one by one, starting at Layer 7, the application layer.
61. 4:21The application layer is the layer that is closest to the end user.
62. 4:26The application layer interacts with software applications that have some communication
63. 4:30component, such as your web browser, whether that’s Brave, Firefox, Chrome, or whatever.
64. 4:37For example HTTP and HTTPS are Layer 7 protocols.
65. 4:43Notice https before cisco.com, indicating that https is being used to get this website
66. 4:50and view it in the browser.
67. 4:53Keep in mind that Layer 7 doesn’t include the application itself, like Chrome or Firefox,
68. 4:58but rather the protocols that interact with the application, like HTTP or HTTPs.
69. 5:06A couple functions of Layer 7 are: identifying communication partners and synchronizing communication.
70. 5:14Let me explain how it does this.
71. 5:18Here I have two OSI model stacks, representing two computers that will communicate with eachother.
72. 5:25The software application, maybe a web browser, interacts with Layer 7, the application layer,
73. 5:30and wants to send some data to the system on the right.
74. 5:34This data is processed through the OSI stack, each layer adding something to the original
75. 5:39data.
76. 5:41This is called ‘ENCAPSULATION’, because the original data is encapsulated inside this
77. 5:46additional information which is added on.
78. 5:50By the time it reaches the physical layer, it is electrical signals on a wire, and is
79. 5:55sent to the neighboring system.
80. 5:57Then, the neighboring system performs the opposite process, the additions of each layer
81. 6:03are stripped off until the data reaches the application layer of the neighboring system.
82. 6:09This process is called ‘de-encapsulation’, as the additional information is removed as
83. 6:14the data is processed up the stack.
84. 6:18Both the encapsulation and de-encapsulation processes are examples of ‘Adjacent-layer
85. 6:23interaction’, interaction between the different layers of the OSI model.
86. 6:27However, the communication between the application layers of the two different systems, is called
87. 6:32same-layer interaction.
88. 6:35This same-layer interaction between application Layers is what allows the application layer
89. 6:40to perform its functions of identifying communication partners, synchronizing communications, etc.
90. 6:47Layer 6 of the OSI is the presentation layer.
91. 6:53Data in the application is in an ‘application format’, a format that applications understand.
92. 6:58It needs to be translated to a different format to be sent over the network.
93. 7:04the presentation layer’s job is to translate between application and network formats.
94. 7:10One example of a function of the presentation layer is encryption of data as it is sent,
95. 7:14so that only the intended recipient can read it, and of course decryption as it is received.
96. 7:21The presentation layer also translates between different application-layer formats, to ensure
97. 7:26that the data is in a format the receiving host can understand.
98. 7:31To summarize, the presentation layer translates data to the appropriate format.
99. 7:35That’s all you really need to know about the presentation layer.
100. 7:40Layer 5 of the OSI model is the session layer.
101. 7:44The session layer controls dialogues, also known as sessions, between communicating hosts.
102. 7:50It establishes, manages, and terminates connections between the local application (for example
103. 7:55your web browser) and the remote application, for example, YouTube.
104. 8:00YouTube’s servers are being used by countless people at every moment, and there has to be
105. 8:05a way to manage all of these sessions.
106. 8:08That’s the purpose of the session layer of the OSI model.
107. 8:11So, we’ve looked at the top 3 layers of the OSI model.
108. 8:17From Top to bottom, application, presentation, and session.
109. 8:22It’s important to know what the functions of these layers are, but actually network
110. 8:27engineers don’t really work with these layers of the OSI model.
111. 8:31That is the job of application developers.
112. 8:35Application developers work with the top layers of the OSI model to connect their applications
113. 8:40over networks.
114. 8:42Let’s return to this diagram.
115. 8:44Remember what I said about encapsulation?
116. 8:47Well, data prepared at the top 3 layers is then sent over to the bottom 4 layers, which
117. 8:54actually do the work of sending it over the network.
118. 8:57After the top 3 layers hand data over to the bottom 4 layers, The next step before sending
119. 9:03data is that Layer 4, the transport layer, adds a header in front of the data, like this.
120. 9:10So, let’s look into the Transport layer a little bit.
121. 9:16Layer 4 of the OSI model is the transport layer.
122. 9:20It segments and reassembles data for communications between end hosts.
123. 9:25To reword that, it breaks large pieces of data into smaller segments which can be easily
124. 9:31sent over the network and are less likely to cause transmission problems if errors occur.
125. 9:37For example, if data wasn’t segmented and you were trying to watch a video, if an error
126. 9:42occurred that prevented the video from reaching your computer, you wouldn’t be able to watch
127. 9:47the video at all.
128. 9:49However, if the data is segmented into many small units, and only one fails to reach the
129. 9:54destination, that’s not a big problem.
130. 9:57The video might skip for a second, but then will continue on just fine.
131. 10:02Also, the Transport layer provides host-to-host communication, also known as end-to-end communication.
132. 10:11This also provides process-to-process communications for applications.
133. 10:16Now let’s review.
134. 10:18Data is prepared by the top 3 layers.
135. 10:21a Layer 4 header is added on.
136. 10:24Note that at this point in the process, this unit of data plus Layer 4 header is called
137. 10:30a segment.
138. 10:32Remember, if the data being sent is large enough, it will actually be segmented into
139. 10:37smaller parts, and a Layer 4 header will be added on to each segment.
140. 10:42Next, that segment is passed on to Layer 3.
141. 10:46And another header is added on to the end, like this.
142. 10:51Layer 3 of the OSI model is the Network Layer.
143. 10:55The network layer provides connectivity between end hosts on different networks, for example
144. 11:00outside of the local area network, or LAN, which we mentioned briefly in the Day 1 video.
145. 11:07Layer 3 provides logical addressing, in the form of IP addresses, something you’ve probably
146. 11:13heard of before.
147. 11:15Layer 3 also provides path selection between source and destination.
148. 11:21Often there are many possible paths which data can take to reach its destination, especially
149. 11:26over a huge network like the Internet.
150. 11:30Layer 3 provides the means of selecting the best path.
151. 11:34Routers operate at Layer 3.
152. 11:36Remember in Day 1’s video I said that routers are used when end hosts need to reach a destination
153. 11:41outside of their LAN?
154. 11:43That’s because routers are Layer 3 devices.
155. 11:47Let’s review the encapsulation process again.
156. 11:51Data is prepared by the upper layers, the transport layer adds a layer 4 header, and
157. 11:57this combination of data plus layer 4 header is called a segment.
158. 12:02next the network layer adds a layer 3 header, including information like the source and
159. 12:08destination IP address, to the segment.
160. 12:11This combination of data, layer 4 header, and layer 3 header, is called a packet.
161. 12:18Next, the packet is further encapsulated at Layer 2, , this time with both a Layer 2 header
162. 12:25AND a Layer 2 trailer.
163. 12:28Layer 2 of the OSI model is the Data Link Layer.
164. 12:32The data link layer provides node-to-node connectivity and data transfer.
165. 12:38For example, direct connections between a PC and a switch, or a switch and a router,
166. 12:44or a router and a router. because Layer 2 is adjacent to Layer 1, the physical layer,
167. 12:50it also defines how data is formatted for transmission over a physical medium, like
168. 12:55copper UTP cables.
169. 12:58Layer 2 also detects, and possibly corrects, errors that occur on the physical layer.
170. 13:05Like layer 3, layer 2 also uses an addressing system, however it is separate and different
171. 13:11from layer 3 addressing.
172. 13:14Finally, switches operate at Layer 2.
173. 13:18Switches look at the destination Layer 2 address to determine where to send the data,
174. 13:24Let’s look at the encapsulation process once more.
175. 13:28Data is prepared by the application layer.
176. 13:32A layer 4 header is added to the data to make a segment.
177. 13:36A Layer 3 header is added to the segment to make a packet.
178. 13:40Remember, the IP address is included in this Layer 3 header.
179. 13:44Then, a layer 2 header and layer 2 trailer are added to the packet.
180. 13:51At this point, the combination of data, layer 4 header, layer 3 header, layer 2 header and
181. 13:58layer 2 trailer is called a frame.
182. 14:01Now, the data is not further encapsulated at Layer 1.
183. 14:05This frame is then sent over the connection, whether it’s electrical signals over a wire
184. 14:11or wireless signals in the case of wifi, to the neighboring system.
185. 14:15Let’s look at layer 1 of the OSI model a bit before moving on.
186. 14:21Layer 1 of the OSI model is the physical layer.
187. 14:25The physical layer defines physical characteristics of the medium used to transfer data between
188. 14:30devices.
189. 14:32For example, voltage levels, maximum transmission distances, like the maximum cable lengths
190. 14:38mentioned in Day 2’s video, physical connectors, cable specifications, etc.
191. 14:46Digital bits are converted into electrical signals, for wired connections, or radio signals,
192. 14:52for wireless connections, like Wi-Fi. as I mentioned before, all of the information in
193. 14:58Day 2’s video, such as cables and pin layouts, is related to the physical layer of the OSI
194. 15:04model.
195. 15:05Okay, now we’ve got a complete frame, and that frame will be sent from the local device
196. 15:12over this cable, let’s say its an ethernet cable.
197. 15:17Once it reaches the remote device, the reverse process of encapsulation, de-encapsualtion,
198. 15:22takes place.
199. 15:25the data link layer translates the raw physical data into a complete frame once again.
200. 15:31Then the layer 2 header and trailer are removed, leaving the Layer 3 packet.
201. 15:36The layer 3 header is removed, leaving the Layer 4 segment.
202. 15:41Finally, the layer 4 header is removed and we are left with the original data prepared
203. 15:46by the upper layers of the original device.
204. 15:49That’s the process of de-encapsulation.
205. 15:53Before moving on, I want to review some terms.
206. 15:56So, when an application wants to send data to another system, it interacts with the application
207. 16:03layer of the OSI stack and the data is prepared to be sent.
208. 16:08When the layer 4 header is added at the transport layer, what is this combination of data plus
209. 16:13Layer 4 header called?
210. 16:15It’s called a Segment.
211. 16:17Then, the Layer 3 header is added on at the Network layer, remember that includes the
212. 16:23IP address.
213. 16:24What’s this now called?
214. 16:26It’s called a packet.
215. 16:29Finally, a Layer 2 header and trailer are added at the Data Link layer.
216. 16:33What’s this complete unit called? It’s called a frame.
217. 16:38Now, there is one new term that is used to refer to all of these.
218. 16:43These are all called Protocol Data Units, or PDUs.
219. 16:48For example, segment is the term for a Layer 4 PDU, Packet is the term for a Layer 3 PDU,
220. 16:56etc.
221. 16:57By the way, at Layer 1, the physical layer, the name for the PDU is bit, referring to
222. 17:02the bits being transferred on the wire.
223. 17:05So, that’s a lot of information.
224. 17:09If you need help remembering the order of the OSI model layers, the flashcards included
225. 17:14in the description should be a big help, but here are a couple acronyms too.
226. 17:18I don’t use acronyms to remember things myself, but many people like them, so here
227. 17:24are a few examples to help you remember.
228. 17:28The first one goes from layer 7 to layer 1, ALL PEOPLE SEEM TO NEED DATA PROCESSING.
229. 17:36Here’s another one, from Layer 1 to Layer 7 this time.
230. 17:42PLEASE DO NOT TEACH STUDENTS POINTLESS ACRONYMS.
231. 17:47If you know any other good ones post them in the comment section!
232. 17:52Now let’s move on from the OSI model, to the TCP/IP suite.
233. 17:58Like the OSI model, it is a conceptual model and set of communications protocols, and in
234. 18:04TCP/IPs case it is used in the Internet and other networks.
235. 18:08It is known as TCP/IP because those are two of the foundational protocols in the suite.
236. 18:15It was developed by the United States Department of Defense through DARPA, which is the Defense
237. 18:21Advanced Research Projects Agency.
238. 18:24It has a similar structure to the OSI model, but with fewer layers.
239. 18:29And, it is the model actually in use in modern networks, NOT OSI.
240. 18:34Note, however, that the OSI model still influences how network engineers think and talk about
241. 18:40networks today, which is why it's important to learn.
242. 18:44Now let’s compare the two.
243. 18:47On the left is the OSI model you’re familiar with by now, and on the right is the TCP/IP
244. 18:53Suite’s networking model.
245. 18:56The Application, Presentation, and Session layers of the OSI model are essentially equivalent
246. 19:02to the Application Layer of the TCP/IP model.
247. 19:07Combining them into one actually represents how network engineers tend to think about
248. 19:10networks, since we don’t work much with anything above the Transport Layer, however,
249. 19:17when TALKING about networks, we use the OSI numbering.
250. 19:22For example, i f you say ‘there is a Layer 4 problem in the network’, network engineers will think
251. 19:27of OSI’s Layer 4, the transport layer, not TCP/IP’s Layer 4, the Application Layer.
252. 19:35Moving on, the OSI model and the TCP/IP model both share the transport layer.
253. 19:41The network layer of the OSI model maps to the Internet layer of the TCP/IP model.
254. 19:48Finally, the data link and Physical layers of the OSI model are equivalent to the Link
255. 19:54layer of the TPC/IP model.
256. 19:57Once again, though, if people say, for example, there is a Layer 2 problem in the network,
257. 20:02they are referring to the OSI Model’s Layer 2, the Data Link Layer, not TCP/IP’s layer
258. 20:082, the Internet layer.
259. 20:10Keep that in mind.
260. 20:13Although TCP/IP is the model actually in use in modern day networks, we still talk about
261. 20:19networks using the OSI model language.
262. 20:22Now, you might hear different names used for these layers.
263. 20:27This is a chart off of Wikipedia showing different naming systems used.
264. 20:31Don’t worry about memorizing all of these, but just keep in mind you might here different
265. 20:37names than the ones I taught you.
266. 20:40For example, the Link layer might be called the network interface, or network access layer.
267. 20:46I actually like this 5 layer model, because it combines the top 3 layers that we, network
268. 20:52engineers, don’t really think about into one, but it keeps the data link and physical
269. 20:57layers separate, and I think its good to think of them as two separate layers.
270. 21:03Before finishing up this lesson and moving on to the quiz, I want to show you this excellent
271. 21:07diagram which I found on Wikipedia.
272. 21:11It demonstrates the process of a host, Host A, sending data to Host B, with two routers
273. 21:16in between.
274. 21:19Here you see the four devices, Host A, connected to a router, connected to another router,
275. 21:26connected to Host B. Here is the TCP/IP stack on each device.
276. 21:33Note that, for forwarding data from host to host, these routers don’t need to be aware
277. 21:38of the higher layers, so only the Internet and Link layers are present here.
278. 21:43So, let’s walk through the process.
279. 21:47An application on Host A wants to communicate with an application on Host B. Let’s say
280. 21:53it’s a Skype conversation, so Host A is sending a little bit of video and audio data
281. 21:59to Host B. Skype interacts with the application Layer, and the data is encapsulated via the
282. 22:06Transport, Internet, and Link Layers.
283. 22:10Then, it is forwarded over to the Router, probably via Ethernet UTP copper cabling.
284. 22:17Remember, Routers are Layer 3 devices, so they want to know the Layer 3 IP address to
285. 22:23know where to forward the data next.
286. 22:25So, de-encapsulation occurs at the Link layer, and then at the Internet layer the router
287. 22:31looks at the destination IP address to know where to send the packet.
288. 22:36Then, the packet is once again encapsulated to make a Frame.
289. 22:41From here it is sent to another router, perhaps over long-distance fiber cabling.
290. 22:47At the Link Layer of this second router, de-encapsulation occurs again, and this router also checks
291. 22:53the destination IP address.
292. 22:56Once it knows where to send the packet, it is once again encapsulated, and sent over
293. 23:01some medium, Ethernet cabling in this case, to Host B. Now de-encapsulation takes place
294. 23:08once more.
295. 23:10Here at the link layer it is a frame.
296. 23:13The header and trailer are removed, and it becomes a packet.
297. 23:18The header is removed, and it becomes a segment.
298. 23:22Finally, the transport layer header is removed, and the application layer on Host B receives
299. 23:28the data and interacts with the application on Host B. So, this has achieved process-to-process
300. 23:35communication, between Skype on Host A and Skype on Host B. Of course, this process will
301. 23:42happen many many times in both directions during the duration of a skype call.
302. 23:48As I mentioned before, this is known as same-layer interaction.
303. 23:52Also, I mentioned the transport layer providers host-to-host communications before.
304. 23:59This diagram indicates that as well.
305. 24:02This Transport layer segment was never changed during this whole process, it is as if it's
306. 24:07direct communication between the two hosts.
307. 24:11Finally, remember that, because the TCP/IP protocols are all industry standard protocols
308. 24:17used by all makers, it doesn’t matter what kind of PCs or router you’re using.
309. 24:23An Apple iMac can communicate with a Cisco router, which can communicate with a Juniper router,
310. 24:29which can communicate with a Dell PC.
311. 24:31That’s the importance of having industry standards.
312. 24:36Okay, that was another lesson with a lot of information.
313. 24:41Once again, there will be supplementary materials to help you remember everything.
314. 24:45There will, of course, be an end-of-video quiz, coming up from the next slide.
315. 24:52There will also be pre-made flash cards to help you memorize what you need to remember,
316. 24:56check the link in the description.
317. 24:58Finally, for this video I will again include a Packet Tracer practice lab, which will use
318. 25:03an interesting feature of packet tracer called ‘simulation mode’ to analyze network traffic.
319. 25:08Now let’s go to the quiz.
320. 25:12HTTP data sent from a YouTube web server is displayed via your web browser.
321. 25:19This is an example of what?
322. 25:22A, adjacent-layer interaction.
323. 25:25B, same-layer interaction.
324. 25:28C, encapsulation.
325. 25:32Or D, de-encapsulation.
326. 25:35Pause the video to think about your answer...
327. 25:40the answer is B, same-layer interaction.
328. 25:45Let’s check the options.
329. 25:49Adjacent-layer interaction refers to interaction between different layers of the OSI model.
330. 25:55In this case, both YouTube’s web server and your web browser are operating at Layer
331. 26:017 using HTTP.
332. 26:03So A, adjacent-layer interaction, is incorrect.
333. 26:08Although encapsulation and de-encapsulation of data surely happened many times as the
334. 26:13data was sent from YouTube’s web server to your web browser, they are not descriptions
335. 26:18of the interaction between YouTube and your browser.
336. 26:21So c, encapsulation, and d, de-encapsulation, are incorrect.
337. 26:29Same-layer interaction refers to interaction between the same layer on different hosts,
338. 26:34in this case the application layer of YouTube’s web server and the browser on your PC.
339. 26:40The concept of same-layer interaction allows you to ‘ignore’ the other layers involved
340. 26:45and focus on interactions between a single layer on different devices.
341. 26:50So b, same-layer interaction, is the correct answer.
342. 26:54let’s go to question 2.
343. 26:57HTTP data has been encapsulated with three separate headers and one trailer.
344. 27:03What is the appropriate name for this PDU?
345. 27:06A, packet.
346. 27:08B, segment.
347. 27:11C, frame.
348. 27:14Or D, data.
349. 27:16Pause the video to think about your answer...
350. 27:23The answer is C, Frame.
351. 27:26Let’s check.
352. 27:28Packet refers to the OSI Layer 3 PDU.
353. 27:32It would have two headers (the Layer 4 header, and the Layer 3 header) and no trailer.
354. 27:38So a, packet, is incorrect.
355. 27:42Segment refers to the OSI Layer 4 PDU.
356. 27:46It would have one header (the Layer 4 header), and no trailer.
357. 27:51So b, segment, is incorrect.
358. 27:55Data refers to the upper-layer data before being encapsulated.
359. 27:59It would have no headers or trailer.
360. 28:02So d, data, is incorrect.
361. 28:06Frame refers to the OSI Layer 2 PDU.
362. 28:10It has three headers (Layer 4, Layer 3, and Layer 2 headers) and one trailer (the Layer 2
363. 28:17trailer).
364. 28:18So c, frame, is the correct answer.
365. 28:21Let’s go to question 3.
366. 28:25Which layers of the OSI model are most relevant to the role of a network engineer?
367. 28:30A, transport, network, data link, and physical.
368. 28:36B, transport, network, and data link.
369. 28:40C, network only, or D, applicaton, presentation, and session.
370. 28:48Pause the video to think about your answer...
371. 28:54the answer is A, transport, network, data-link, and physical.
372. 29:00Let’s check.
373. 29:02Although these layers are very relevant to the duties of a network engineer, the physical
374. 29:07layer is missing.
375. 29:08So b, transport, network, and data link, is incorrect.
376. 29:14Although the Network layer is very relevant to network engineers of course , it is not the only one.
377. 29:20So c, network only, is incorrect.
378. 29:25These layers of the OSI model are not generally relevant to the role of a network engineer.
379. 29:30They are relevant to application developers.
380. 29:33So D, application, presentation, and session, is incorrect.
381. 29:40These four lower layers of the OSI models are all very relevant to the role of a network
382. 29:45engineer.
383. 29:46So a, transport, network, data link, and physical, is the correct answer.
384. 29:53Lets go to the next question.
385. 29:57The Link layer of the TCP/IP Model is equivalent to what layer, or layers, of the OSI Model?
386. 30:04A, transport and network.
387. 30:08B, network and data link.
388. 30:11C, data link.
389. 30:13Or D, data link and physical.
390. 30:16Pause the video to think about your answer...
391. 30:22the correct answer is D, data link and physical.
392. 30:26Let’s check.
393. 30:29The OSI Transport layer is equivalent to the TCP/IP Transport layer, and the OSI Network
394. 30:34layer is equivalent to the TCP/IP Internet layer.
395. 30:38So a, transport and network layers, is incorrect.
396. 30:45The OSI Network layer is equivalent to the TCP/IP Internet layer.
397. 30:50The OSI Data Link layer is equivalent to part of the TCP/IP Link layer, but it is not totally
398. 30:56equivalent.
399. 30:57So b, network and data link layers, and c, data link layer, are incorrect.
400. 31:05The combined functions of the OSI Data Link and Physical layers are equivalent to the
401. 31:09TCP/IP Link layer.
402. 31:12So d, data link and physical layers, is the correct answer.
403. 31:16Let’s go to the last quiz question for this video.
404. 31:21Which layer of the OSI model provides host-to-host communications?
405. 31:25A, application, b, network, c, transport, or d, data link.
406. 31:33Pause the video to think about your answer...
407. 31:40the answer is c, transport.
408. 31:43Let’s check.
409. 31:45The Application layer provides process-to-process communications, not host-to-host.
410. 31:51So a, application layer, is incorrect.
411. 31:54The Network and Data Link layers do not provide end-to-end, host-to-host communications.
412. 32:02So b, network, and d, data link, are incorrect.
413. 32:08The Transport layer provides host-to-host communications, as shown in this diagram.
414. 32:12So c, Transport, is the correct answer.
415. 32:16Thank you for watching.
416. 32:20That's all for this video.
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