WEBVTT - Dip Into the 7 Layers of the OSI Model 0:00:04.160 --> 0:00:07.160 Get in text with technology with tech Stuff from how 0:00:07.240 --> 0:00:13.280 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:13.320 --> 0:00:15.920 I am your host, Jonathan Strickland. I'm an executive producer 0:00:15.960 --> 0:00:20.680 at how stuff Works and I love technology. You guys, 0:00:21.200 --> 0:00:23.640 you may or may not be aware that I live 0:00:23.760 --> 0:00:27.160 stream text stuff whenever it's just me and I don't 0:00:27.160 --> 0:00:30.240 have a guest or or a co host. I live 0:00:30.280 --> 0:00:34.040 stream out on twitch dot tv slash tech stuff, and 0:00:34.159 --> 0:00:36.800 one of the features that Twitch has is a chat room, 0:00:36.880 --> 0:00:41.000 so I often engage in chat in said chat room, 0:00:41.040 --> 0:00:44.000 and occasionally I asked people, Hey, is there anything you 0:00:44.040 --> 0:00:46.240 would like me to talk about in a future episode 0:00:46.280 --> 0:00:49.640 of tech Stuff And Nick k a k A dirt 0:00:49.640 --> 0:00:53.519 burr over at the Twitch chat room suggested the os 0:00:53.600 --> 0:00:56.720 I model, the seven layers of the O S I model, 0:00:57.160 --> 0:00:59.400 and I thought, you know what, I have never actually 0:00:59.520 --> 0:01:04.120 done an episode about the O SI model, and challenge 0:01:04.160 --> 0:01:07.040 has been accepted. The gauntlet was thrown picked up, and 0:01:07.120 --> 0:01:10.920 here we go. The seven layer O SI model is 0:01:10.959 --> 0:01:15.600 an interesting topic. It's typically one that's taught in computer 0:01:15.680 --> 0:01:19.920 science and telecommunications classes. It's it's a networking thing. It's 0:01:20.040 --> 0:01:22.880 not necessarily internet. You would usually talk about t c 0:01:23.000 --> 0:01:26.440 P i P protocols for Internet models of networking, but 0:01:26.480 --> 0:01:31.240 it is for computer networks in general. And before I 0:01:31.319 --> 0:01:34.800 get into this too far with this whole concept of 0:01:34.840 --> 0:01:37.520 the seven layers of the O SI model, I gotta 0:01:37.560 --> 0:01:41.720 make something very very clear. The seven layers are not 0:01:41.880 --> 0:01:46.280 actual physical layers. Even though there is one layer called 0:01:46.319 --> 0:01:49.320 the physical layer, they are not physical layers to any 0:01:49.320 --> 0:01:51.920 sort of system. This is not some sort of seven 0:01:52.040 --> 0:01:54.880 layer DIP situation, which is too bad because that stuff 0:01:54.960 --> 0:01:59.840 is of course delicious. This is a conceptual model, and 0:02:00.320 --> 0:02:03.920 it's a way to imagine the interactions, the rules, the 0:02:03.960 --> 0:02:09.359 protocols between various elements within a telecommunications network to make 0:02:09.400 --> 0:02:13.000 it easier to comprehend what is actually going on. Or, 0:02:14.200 --> 0:02:17.960 as Eli the Computer Guy said in an incredibly useful 0:02:18.040 --> 0:02:20.440 video on YouTube, you can actually search for Eli the 0:02:20.440 --> 0:02:22.680 Computer Guy and look for the us I model. You 0:02:22.680 --> 0:02:26.080 can actually watch this video. Uh. The model breaks down 0:02:26.440 --> 0:02:30.680 the components of network communication into layers to make it 0:02:30.720 --> 0:02:33.000 easier to understand what is actually going on. So, in 0:02:33.000 --> 0:02:36.480 a way, the seven layer O SI model is sort 0:02:36.520 --> 0:02:39.160 of like the analogies I tend to use on this 0:02:39.280 --> 0:02:42.920 show in order to explain various concepts. It's meant to 0:02:42.960 --> 0:02:47.280 clarify the purposes of various design elements and different protocols 0:02:47.400 --> 0:02:50.280 and and tasks. By the way, there will be many 0:02:50.320 --> 0:02:53.840 analogies in this episode because I love them. I was 0:02:53.880 --> 0:02:56.160 an English major, so that's kind of my go too. 0:02:56.560 --> 0:02:58.880 There are also other models, Like I said, there's the 0:02:58.919 --> 0:03:02.680 Internet Protocol Suite. That's the other standard model of computer networking. 0:03:02.960 --> 0:03:05.200 But we're going to focus on the O SI model 0:03:05.240 --> 0:03:08.079 for this episode. Maybe someday I'll do an episode about 0:03:08.120 --> 0:03:10.119 the t C P I P model, but that will 0:03:10.160 --> 0:03:13.360 not be this episode. They are similar in many ways, 0:03:13.400 --> 0:03:16.080 but there are distinctions between the two. But it's really 0:03:16.120 --> 0:03:20.200 just a way of thinking about how these communication networks 0:03:20.280 --> 0:03:23.440 handle tasks. The OSI model, by the way, did not 0:03:23.600 --> 0:03:26.320 just spring up out of whole cloth either. It's the 0:03:26.320 --> 0:03:31.200 product of an organization called the International Standards Organization or ISO, 0:03:31.400 --> 0:03:35.880 not I S o IO. So let's learn about that 0:03:36.000 --> 0:03:38.880 group first before we talk about the model. Is SO 0:03:39.120 --> 0:03:43.840 is a non governmental international organization that is completely independent 0:03:43.880 --> 0:03:46.920 of any state authority, so it doesn't fall under the 0:03:46.920 --> 0:03:51.240 purview of any one nation's government. Uh. The membership of 0:03:51.280 --> 0:03:55.800 the of ISO includes a hundred sixty two national standards bodies, 0:03:56.360 --> 0:04:00.320 there's only one is a member per country, so you 0:04:00.400 --> 0:04:05.360 can't have multiple standards organizations from one country in ISO's roster. 0:04:05.880 --> 0:04:10.240 It has to be the foremost standards organization of that country. 0:04:10.600 --> 0:04:15.440 The United States, for example, has a member. Or there's 0:04:15.440 --> 0:04:19.000 an organization that is in ISO is the American National 0:04:19.120 --> 0:04:23.640 Standards Institute or and C. And C actually predates ISO. 0:04:23.760 --> 0:04:27.480 Has and C was founded in nineteen eighteen. IO began 0:04:27.520 --> 0:04:30.680 in nineteen More on the founding of ISO in just 0:04:30.760 --> 0:04:34.880 a second. And c's purpose is to accredit standards that 0:04:34.920 --> 0:04:38.440 are created by quote qualified groups in the quote. So, 0:04:38.480 --> 0:04:41.599 in other words, this organization the United States does not 0:04:41.800 --> 0:04:45.280 create standards. It's not the one that says, this is 0:04:45.400 --> 0:04:50.520 what the standard X is from now on, you all 0:04:50.560 --> 0:04:52.919 have to follow it. This is the X by which 0:04:52.960 --> 0:04:56.159 all other x is must be measured. They don't do that. 0:04:56.400 --> 0:04:58.480 What they do is they look at the work of 0:04:58.960 --> 0:05:03.200 qualified groups and say, yes, this example of whatever that 0:05:03.279 --> 0:05:07.719 thing is is the standard against which all others shall 0:05:07.760 --> 0:05:12.320 be judged. So mote it be at this point it 0:05:12.400 --> 0:05:14.720 might even be good for us to just consider what 0:05:14.760 --> 0:05:17.360 the heck a standard is in the first place, because 0:05:17.360 --> 0:05:20.760 otherwise this just becomes a jumble of words, and I 0:05:20.760 --> 0:05:24.680 start using phrases that don't really mean anything to you, 0:05:24.680 --> 0:05:27.520 You're gonna totally tune out. So the definition of standard 0:05:27.600 --> 0:05:32.359 is according to the Miriam Webster Dictionary. Your definitions may 0:05:32.480 --> 0:05:35.680 vary depending on the dictionary of use. It includes the 0:05:35.880 --> 0:05:40.480 definition of something established by authority, custom or general consent 0:05:40.640 --> 0:05:44.480 as a model or example, or something set up and 0:05:44.640 --> 0:05:50.080 established by authority as a rule for the measure of quantity, weight, extent, value, 0:05:50.279 --> 0:05:54.080 or quality. It could also be a giant flag that 0:05:54.120 --> 0:05:57.919 you carry into battle. But that definition probably doesn't really 0:05:57.960 --> 0:06:00.279 apply when it comes to the O S. I'm also 0:06:00.279 --> 0:06:03.560 we're not gonna think about it right now. Standards are 0:06:03.640 --> 0:06:07.520 an agreed upon model upon which all other instances of 0:06:07.560 --> 0:06:12.320 that concept or physical object should be measured. Uh So, 0:06:12.760 --> 0:06:16.760 units of measurements are standards that are easy to understand. Right. 0:06:16.800 --> 0:06:18.840 An inch is an inch no matter where you go. 0:06:20.040 --> 0:06:22.640 A kilogram is a kilogram no matter where you go. 0:06:23.400 --> 0:06:26.400 That sort of thing. So organizations like ants and is 0:06:26.600 --> 0:06:29.880 so help establish these standards. They don't necessarily come up 0:06:29.880 --> 0:06:32.760 with them, but they might accredit them, they might endorse them, 0:06:32.760 --> 0:06:37.120 and thus get widespread acceptance of that as a standard, 0:06:37.720 --> 0:06:40.640 this becomes sort of a generally agreed upon common concept 0:06:40.680 --> 0:06:44.680 across multiple nations. The need for standards was apparent from 0:06:44.680 --> 0:06:47.680 the early days of trade, because merchants had to create 0:06:47.760 --> 0:06:50.880 standards so that trade systems could actually work across different 0:06:50.880 --> 0:06:54.880 currencies and regions, not to mention, create standards of measurements 0:06:54.960 --> 0:06:56.880 so they could make sure they were talking about the 0:06:56.880 --> 0:07:00.000 same amount of stuff they were selling from place to play. 0:07:00.560 --> 0:07:03.360 If you're a if you're a spice merchant, you want 0:07:03.400 --> 0:07:06.479 to make sure the people you're selling to understand the 0:07:06.560 --> 0:07:08.960 quantities you're talking about. So you had to set up 0:07:08.960 --> 0:07:12.400 these standards that people would generally agree to in order 0:07:12.440 --> 0:07:14.920 to actually make trade work. It was necessary for that 0:07:15.000 --> 0:07:17.560 sort of thing. Well, the same thing is true in 0:07:17.720 --> 0:07:20.760 technology in general, not just with units of measurement things 0:07:20.760 --> 0:07:24.720 that are more kind of ultimately tangible, but with general 0:07:24.760 --> 0:07:27.360 concepts where you're gonna have lots of different people from 0:07:27.400 --> 0:07:30.440 all over the world working within those sort of concepts, 0:07:30.680 --> 0:07:33.760 and you want there to be interoperability between all of 0:07:33.760 --> 0:07:37.160 those people. You have to create these standards so that 0:07:37.600 --> 0:07:40.120 everyone is kind of working from the same basic set 0:07:40.120 --> 0:07:42.920 of rules, and by working from the same basic, basic 0:07:42.960 --> 0:07:50.040 set of rules. You you reduce the possibility of incompatibilities. 0:07:51.080 --> 0:07:55.160 There will always be incompatibilities just because technology doesn't always 0:07:55.160 --> 0:07:57.160 work the way we intended it to. But you can 0:07:57.200 --> 0:07:59.560 at least remove some of those barriers early on in 0:07:59.600 --> 0:08:02.640 the des line process by agreeing upon a basic set 0:08:02.640 --> 0:08:05.880 of rules from the start. That's the whole purpose of 0:08:06.040 --> 0:08:12.360 organizations like ISO SO. This extends to telecommunication and networking layers. 0:08:13.000 --> 0:08:16.720 As ISSO states on its web page, international standards make 0:08:17.000 --> 0:08:22.080 things work. They give world class specifications for products, services, 0:08:22.120 --> 0:08:26.800 and systems to ensure quality, safety, and efficiency. Now, i 0:08:26.920 --> 0:08:29.400 SO got its start back in nineteen forty six during 0:08:29.400 --> 0:08:32.920 a meeting of the Institute of Civil Engineers in London, England, 0:08:32.960 --> 0:08:35.840 and there were representatives from twenty five different countries that 0:08:35.880 --> 0:08:39.200 attended that meeting, and they concluded that they needed an 0:08:39.240 --> 0:08:44.520 official but independent organization to help coordinate and unify industrial standards. 0:08:44.520 --> 0:08:48.960 I would become an official entity on February twenty third, 0:08:49.080 --> 0:08:52.719 nineteen forty seven, and according to ISO, the organization has 0:08:52.720 --> 0:08:58.280 published nearly twenty two thousand international standards since it was founded. 0:08:58.840 --> 0:09:01.720 Oh and uh ice SO is not an acronym. It 0:09:01.840 --> 0:09:04.319 is not I s O. It is ISO. It is 0:09:04.360 --> 0:09:08.559 all capitalized, but still it's ISO. And it's because if 0:09:08.559 --> 0:09:11.040 you translate the name of the organization into the different 0:09:11.120 --> 0:09:14.559 languages of all the different countries that have a an 0:09:14.679 --> 0:09:18.000 organization that's a member of ISO, you don't end up 0:09:18.080 --> 0:09:21.960 with words that start with I, S and O with 0:09:22.080 --> 0:09:25.800 every translation. Right. That's just the English version. So the 0:09:25.800 --> 0:09:30.160 English version is International Standards Organization. But other languages have 0:09:30.360 --> 0:09:33.600 it in different orders or even different words. So you 0:09:33.640 --> 0:09:36.600 can't just call it an acronym because not every country 0:09:37.559 --> 0:09:42.160 uses the same the same language, right, So they decided 0:09:42.200 --> 0:09:44.480 instead they would take their name from a Greek word 0:09:44.559 --> 0:09:49.559 ISOs i S O s which means equal so is 0:09:49.800 --> 0:09:52.400 so is always is so no matter what language you 0:09:52.440 --> 0:09:55.719 are speaking. As for the O S I model, now, 0:09:55.760 --> 0:09:58.720 that actually emerged from a couple of different projects that 0:09:58.800 --> 0:10:02.840 we're trying to ablish a framework for network systems. This 0:10:02.880 --> 0:10:06.160 would be in the seventies when networks were really starting 0:10:06.200 --> 0:10:10.640 to become a possibility. You may remember that ARPA net 0:10:10.720 --> 0:10:13.960 had been in the development stages in the sixties and seventies, 0:10:14.400 --> 0:10:17.480 and that was a precursor to the Internet. It was 0:10:17.520 --> 0:10:22.320 also those early early days of networking different devices together 0:10:22.440 --> 0:10:25.120 so that they could communicate directly to one another instead 0:10:25.120 --> 0:10:29.439 of having to work on one machine, save your work 0:10:29.559 --> 0:10:33.599 on some form of physical media, maybe it's a magnetic 0:10:33.679 --> 0:10:36.640 disc or real to real tape or whatever, taking that 0:10:36.760 --> 0:10:40.160 physical media over to another and I guess I should 0:10:40.200 --> 0:10:44.000 say medium over to another device and then loading it 0:10:44.080 --> 0:10:46.040 up there. Instead of doing that, you can have them 0:10:46.120 --> 0:10:49.200 communicate directly to one another using a network solution. But 0:10:49.240 --> 0:10:54.040 you had to establish those standards, particularly since there were 0:10:54.080 --> 0:10:57.600 lots of different computers that were being produced and lots 0:10:57.600 --> 0:11:00.160 of other devices that you also would want to net 0:11:00.200 --> 0:11:03.840 computers too, and they didn't all use the same sort 0:11:03.880 --> 0:11:07.240 of operating systems, they didn't communicate in the same way, 0:11:07.800 --> 0:11:10.680 So you had to create a set of standards that 0:11:10.720 --> 0:11:16.320 would work across multiple instances of networked machines so that 0:11:16.400 --> 0:11:21.640 you didn't just end up with different specific network protocols 0:11:21.800 --> 0:11:25.439 for very specific instances. Let's say that one place has 0:11:25.559 --> 0:11:28.719 all the same sort of mainframe style computers, so they 0:11:28.760 --> 0:11:31.800 design a network that only works with those. That's not 0:11:31.840 --> 0:11:34.880 any use to somebody who's trying to create a network 0:11:34.960 --> 0:11:37.400 for a totally different type of machines. So they wanted 0:11:37.400 --> 0:11:39.880 to create this basic set standards. In the seventies, you 0:11:39.880 --> 0:11:42.800 had two different groups doing that, and eventually those two 0:11:42.840 --> 0:11:46.240 groups they got their work kind of merged together, and 0:11:46.360 --> 0:11:49.880 in nineteen eighty three they published this, or at least 0:11:49.880 --> 0:11:53.320 they they submitted this to ISO. UH. It was called 0:11:53.360 --> 0:11:57.599 the Basic Reference Model for Open Systems Interconnection, and i 0:11:57.720 --> 0:11:59.920 SO would publish that model the following year, in nineteen 0:12:00.000 --> 0:12:04.280 eight four. This would be the UH the ISO publication 0:12:04.360 --> 0:12:09.280 number seven thousand. So next time you're at pub trivia 0:12:09.559 --> 0:12:13.200 and someone says, what's the ISO publication number of the 0:12:13.200 --> 0:12:16.400 os I model, you can just pipe up seven and 0:12:16.480 --> 0:12:21.319 you will win great acclaim. I don't know why you're 0:12:21.360 --> 0:12:25.600 going to I T professional pub trivia, but that's you know, 0:12:25.840 --> 0:12:29.840 I'm not judging. So I SO created the O s 0:12:29.880 --> 0:12:32.920 I seven layers model. This again was to create a 0:12:32.960 --> 0:12:36.079 sort of common lexicon across the world for the purposes 0:12:36.120 --> 0:12:40.960 of discussing telecommunication systems. And let's take a high level 0:12:40.960 --> 0:12:46.359 look at what this means. Those seven layers to this model, AH, 0:12:46.800 --> 0:12:51.040 they represent different tasks sort of or or different layers 0:12:51.160 --> 0:12:55.000 of responsibility within a communications network. The bottom most layer, 0:12:55.200 --> 0:12:59.080 layer one is what we call the physical layer, the 0:12:59.120 --> 0:13:03.320 top layer. Lay year seven is the application layer, and 0:13:03.480 --> 0:13:05.480 if you'd like to visualize this in a practical way, 0:13:05.600 --> 0:13:08.520 layer seven is the one that the end user comes 0:13:08.559 --> 0:13:12.840 into contact with. Layer seven is the part of an 0:13:12.840 --> 0:13:17.400 application or program that that you can see. Now it's 0:13:17.440 --> 0:13:21.120 not Layer seven is not an application in of itself, 0:13:21.160 --> 0:13:25.880 although some applications can exist entirely in layer seven. Layer 0:13:25.920 --> 0:13:30.280 seven is the group of services within a communications network 0:13:31.040 --> 0:13:33.800 that interact directly with whatever is going on with the 0:13:33.840 --> 0:13:38.839 application and send that further down the stack. So while 0:13:38.880 --> 0:13:42.880 a web browser is not in itself a layer seven, 0:13:43.760 --> 0:13:49.760 it uses elements that do tie into layer seven. In 0:13:49.760 --> 0:13:52.760 other words, uh, it's it's kind of like the the 0:13:54.200 --> 0:13:58.920 just under the surface layer for whatever application you have 0:13:58.960 --> 0:14:03.760 opened that has this network communication aspect to it, whether 0:14:03.840 --> 0:14:07.320 that's with a phone or a computer or a printer, 0:14:07.559 --> 0:14:11.120 really any device that's connected to a network. This is 0:14:11.160 --> 0:14:13.720 the one that's closest to you. So it's the one 0:14:13.800 --> 0:14:16.360 that's easiest for us to kind of understand because it's 0:14:16.360 --> 0:14:19.840 the stuff that we interact with. You interact with this interface, 0:14:20.000 --> 0:14:23.680 you send commands. Those commands get pushed down the stack 0:14:24.000 --> 0:14:26.440 and depending it depends on what the command is about 0:14:26.480 --> 0:14:29.480 where that ends up going on the other end of 0:14:29.480 --> 0:14:31.840 the model, and we'll go through all the layers in 0:14:31.840 --> 0:14:33.920 this episode, but right now I'm just looking at the top. 0:14:33.960 --> 0:14:36.120 In the very bottom on the other end, the bottom 0:14:36.160 --> 0:14:40.200 of the stack is layer one. That's the physical layer 0:14:40.240 --> 0:14:44.120 of the networking process. This is the basic bit stream. 0:14:44.200 --> 0:14:46.840 This is the zeros and ones that are being carried 0:14:47.080 --> 0:14:51.320 by some means. You could even argue that it's not 0:14:51.360 --> 0:14:54.840 even zeros and ones, it's the stuff that represents those 0:14:54.920 --> 0:14:58.800 zeros and ones. It's the actual electrical impulses or rays 0:14:58.840 --> 0:15:03.800 of light or radio signals that are carrying information. So 0:15:03.880 --> 0:15:08.720 this is the conveyance of data. So that depends upon 0:15:08.840 --> 0:15:14.080 actual physical properties like physical components like cables or Wi 0:15:14.240 --> 0:15:18.200 Fi cards or things of that nature. That is why 0:15:18.240 --> 0:15:21.240 it's called the physical layer. It is completely dependent upon that. 0:15:21.360 --> 0:15:25.120 It does not care about protocols. None of that stuff matters. 0:15:25.160 --> 0:15:32.000 This is just carrying the signal. Uh So, between layers seven, 0:15:32.440 --> 0:15:35.000 the one that we interact with directly, and layer one, 0:15:35.120 --> 0:15:38.920 that physical layer, are all the intervening levels that handle 0:15:39.000 --> 0:15:42.520 protocols for network communication. Again, this these are not physical, 0:15:42.720 --> 0:15:45.680 literal layers, but rather a way to divide up those 0:15:45.720 --> 0:15:49.200 protocols for the purposes of understanding which layers hand tasks 0:15:49.240 --> 0:15:53.360 off to other layers or accept tasks from other layers. 0:15:53.920 --> 0:15:56.440 So I'm gonna explain this conceptual model with an analogy. 0:15:56.760 --> 0:15:58.920 So we're gonna get even more abstract because that's what 0:15:58.960 --> 0:16:00.880 I do, and you can't stop me. It's my show. 0:16:01.440 --> 0:16:03.680 The O S I seven layer model is like a 0:16:03.680 --> 0:16:08.320 metaphorical bucket brigade fighting a fire. So let's say that 0:16:08.440 --> 0:16:11.600 layer one, that physical layer, that's the person in the 0:16:11.640 --> 0:16:14.800 bucket brigade who is closest to the water spigot. Water 0:16:14.960 --> 0:16:18.800 is pouring out of the water spigot. Now, the person 0:16:18.840 --> 0:16:23.240 who's representing layer one can do a couple of different things. 0:16:23.240 --> 0:16:25.920 They can fill up a bucket with water. They can 0:16:25.960 --> 0:16:29.080 hand a full bucket of water over to the person 0:16:29.120 --> 0:16:32.280 who is representing layer two, or they can accept an 0:16:32.280 --> 0:16:34.960 empty bucket from layer two so that they can then 0:16:35.000 --> 0:16:37.560 fill up the bucket of to make it a bucket 0:16:37.560 --> 0:16:41.200 of water. Again, Layer two can really only do a 0:16:41.240 --> 0:16:44.040 couple of things in this particular analogy. They can accept 0:16:44.080 --> 0:16:47.280 an empty bucket from layer three, or they can accept 0:16:47.360 --> 0:16:50.760 a full bucket from layer one and they pass it 0:16:50.840 --> 0:16:53.760 on in continuing in the direction that it was traveling. 0:16:54.120 --> 0:16:55.880 When you get all the way down to layer seven, 0:16:56.320 --> 0:16:59.480 they can accept a full bucket of water from layer six, 0:17:00.160 --> 0:17:03.520 can splash that water onto a fire, and they can 0:17:03.720 --> 0:17:08.359 send a empty bucket down to layer six. That's kind 0:17:08.400 --> 0:17:11.000 of what's going on here from a conceptual level with 0:17:11.160 --> 0:17:18.119 network communication, it's instead of water communication tasks and different 0:17:18.200 --> 0:17:20.560 layers are responsible for different parts of the task. So 0:17:20.600 --> 0:17:22.600 it gets a little more complicated because it's not just 0:17:23.240 --> 0:17:26.280 accept something and pass it on. That's it's not as 0:17:26.280 --> 0:17:28.040 simple as that. There's a little bit more to it. 0:17:28.080 --> 0:17:29.960 But I wanted to start big so you can kind 0:17:29.960 --> 0:17:34.240 of understand that these layers are all dependent upon one another. 0:17:36.040 --> 0:17:40.119 So I hope that analogy makes some sense to you. 0:17:40.240 --> 0:17:42.520 I really liked it because while I was trying to 0:17:42.600 --> 0:17:45.119 kind of digest the OSI model, that's kind of how 0:17:45.160 --> 0:17:48.639 I imagined it was this process of passing down a 0:17:48.760 --> 0:17:52.639 task so that it goes down the chain until it 0:17:52.680 --> 0:17:54.399 hits where it needs to go, comes back up the 0:17:54.480 --> 0:17:57.720 chain with whatever the response is. Now, the reason the 0:17:57.800 --> 0:18:00.240 whole model is important. Why are we even talking about 0:18:00.240 --> 0:18:02.680 the OSI model in the first place, beyond just giving 0:18:02.760 --> 0:18:04.879 us an idea of what's going on behind the scenes 0:18:04.960 --> 0:18:09.880 when you are using devices on a networked system. It's 0:18:09.920 --> 0:18:13.160 because it provides a guide for developers. For one thing, 0:18:13.359 --> 0:18:16.359 if you're developing programs or applications that are meant to 0:18:16.400 --> 0:18:19.600 be networked, it is really good to have an understanding 0:18:19.840 --> 0:18:23.080 of the OSI model so that you can focus on 0:18:23.160 --> 0:18:27.359 the proper way to implement your your program. Uh. And 0:18:27.400 --> 0:18:30.280 it's also important for you to adhere to the standard 0:18:30.359 --> 0:18:33.400 that's been established. That's what standards are for, after all. 0:18:33.640 --> 0:18:35.680 So you might even wonder why is this even important, 0:18:35.720 --> 0:18:38.040 why are we even talking about OSI models? Well, I 0:18:38.040 --> 0:18:40.120 mean beyond just giving us an idea of what's going 0:18:40.160 --> 0:18:43.159 on behind the scenes of devices that are running on 0:18:43.160 --> 0:18:46.520 a network and how that communication is supposed to work 0:18:46.560 --> 0:18:50.280 from a conceptual level, it provides a guide for developers 0:18:50.280 --> 0:18:53.439 who are creating applications and programs that will run on 0:18:53.560 --> 0:18:57.879 networked devices. It's really important that their processes adhere to 0:18:57.920 --> 0:19:00.840 the standard. I mean, that's why we of standards. It's 0:19:00.880 --> 0:19:04.680 to make sure that things are falling in line so 0:19:04.720 --> 0:19:07.480 that the everything is as smooth as it possibly can be, 0:19:07.560 --> 0:19:11.720 especially when you get into interoperability where you have programs 0:19:11.760 --> 0:19:15.680 operating with other programs. If you have that happening, they 0:19:15.720 --> 0:19:18.600 need to agree upon the same basic set of rules. 0:19:19.560 --> 0:19:23.240 Otherwise it's like getting two people together who speak completely 0:19:23.280 --> 0:19:27.640 different languages that have no basis, like there's no shared 0:19:28.119 --> 0:19:32.200 origin for the two languages. They both arose completely independently, 0:19:32.480 --> 0:19:35.960 and then try to have them have a conversation without 0:19:36.160 --> 0:19:38.719 using gestures or anything else to kind of get their 0:19:38.760 --> 0:19:43.320 meeting across. It's it's practically impossible. So this is very 0:19:43.359 --> 0:19:46.800 important for programmers in order to make sure that their 0:19:47.320 --> 0:19:53.719 approach will be interoperable for other types of processes and programs. Uh. 0:19:54.400 --> 0:19:57.080 This could be as simple as making sure that your 0:19:57.160 --> 0:19:59.639 program is not going to make an entire framework on 0:19:59.720 --> 0:20:02.560 stay will and cause potential crashes or other issues, to 0:20:02.680 --> 0:20:05.600 something more complicated such as apps being able to share 0:20:05.600 --> 0:20:09.119 the same data across each other or access each other's 0:20:09.119 --> 0:20:11.720 functionality in some way. And it's only because we have 0:20:11.760 --> 0:20:13.760 these standards in place at such an approach is really 0:20:13.800 --> 0:20:16.840 possible without having different teams worked very tightly with one 0:20:16.840 --> 0:20:19.600 another from the first place. It's also really useful if 0:20:19.600 --> 0:20:22.520 you're a network specialist like an I T network guy 0:20:23.000 --> 0:20:26.560 or a lady because you've got a problem happening in 0:20:26.600 --> 0:20:28.480 a network that you manage, you want to be able 0:20:28.520 --> 0:20:31.560 to identify where that problem is and how you would 0:20:31.560 --> 0:20:34.800 go about solving it, and being able to figure out 0:20:34.840 --> 0:20:38.359 conceptually where in the OSI model that problem may be arising, 0:20:38.400 --> 0:20:40.959 tells you what approach you may need to take in 0:20:41.080 --> 0:20:45.400 order to fix the problem. I've heard that problems fall 0:20:45.440 --> 0:20:48.360 on the physical layer, which essentially means that someone has 0:20:48.359 --> 0:20:50.920 not plugged something in. It sounds like an I T. 0:20:51.080 --> 0:20:53.920 Crowd kind of joke, but apparently it's absolutely true that 0:20:54.000 --> 0:20:56.760 you know, there's folks who just there's a cable that's 0:20:56.760 --> 0:20:59.399 not fully plugged into a port, or someone forgot to 0:20:59.400 --> 0:21:02.240 turn a switch John or something, and a lot of 0:21:02.240 --> 0:21:04.199 the problems do stem from that. And then once you 0:21:04.240 --> 0:21:06.640 get beyond the physical layer, things get real tricky because 0:21:06.640 --> 0:21:09.439 you got to figure out where is the breakdown happening 0:21:09.440 --> 0:21:11.720 and what can you potentially do about it. So it 0:21:11.760 --> 0:21:14.840 does have a practical application outside of of just a 0:21:14.880 --> 0:21:17.879 general information The model is also obviously used as a 0:21:17.880 --> 0:21:22.800 teaching tool to explain computer network architecture and communication protocols, 0:21:23.200 --> 0:21:25.560 and it gives computer science students a foundation and the 0:21:25.640 --> 0:21:29.240 logic they'll need to understand to work within computer network architecture. 0:21:29.640 --> 0:21:32.600 So that's the overview. Now we're gonna take a quick break, 0:21:32.960 --> 0:21:34.919 and then when we come back, we're gonna start waiting 0:21:34.920 --> 0:21:38.200 into what all these layers actually mean. So let's take 0:21:38.320 --> 0:21:47.639 a quick break to thank our sponsor. All right, let's 0:21:47.720 --> 0:21:49.639 look at these layers. Now, we're gonna start at that 0:21:49.720 --> 0:21:52.320 highest layer and work downwards since I think that makes 0:21:52.359 --> 0:21:55.080 the most sense for the average person. Here's a quick overview, 0:21:55.119 --> 0:21:58.159 and then we're gonna dive further into detail. All right. 0:21:58.240 --> 0:22:00.600 Layer seven is the application layer. That's where the end 0:22:00.680 --> 0:22:04.040 user applications live, or at least where they touch. That's 0:22:04.400 --> 0:22:08.200 where they make contact with this OSI model. This would 0:22:08.200 --> 0:22:10.800 be the stuff that we interact with, like whether you're 0:22:10.800 --> 0:22:14.439 playing Pokemon, or you're using a web browser to surf 0:22:14.440 --> 0:22:16.880 the web, or you're checking a fitness app or anything 0:22:16.920 --> 0:22:20.080 that's along those lines where it's tapping into this network. 0:22:20.680 --> 0:22:24.240 You are interfacing with something that is touching on this layer. 0:22:24.640 --> 0:22:26.520 There's a lot more going down below the surface, but 0:22:27.000 --> 0:22:29.800 we'll jump into that in a minute. Next is layer six. 0:22:30.240 --> 0:22:34.879 That's the presentation layer. That layer handles syntax processing. Don't worry. 0:22:34.920 --> 0:22:36.840 I'll explain that in a little bit. It's sort of 0:22:36.880 --> 0:22:40.240 like a translator in many ways, so hold on to 0:22:40.359 --> 0:22:43.879 that idea. Layer five is the session layer. This layer 0:22:43.920 --> 0:22:48.000 manages the flow of events that establish and terminate network connections, 0:22:48.320 --> 0:22:53.720 communication channels, if you will, between applications or devices. Layers 0:22:53.720 --> 0:22:56.359 five through seven, so the ones we just talked about, 0:22:56.520 --> 0:23:02.159 are considered application level data layers. Everything below those layers 0:23:02.280 --> 0:23:06.320 gets into more fundamental aspects of moving data around, where 0:23:06.359 --> 0:23:09.199 it's not so much concerned with it being identified as 0:23:09.200 --> 0:23:14.000 an application. It's more basic than that. It reaches progressively 0:23:14.040 --> 0:23:16.720 more abstract concepts and moving further away from anything we 0:23:16.760 --> 0:23:20.800 would think of as an application. Level four is the 0:23:20.840 --> 0:23:25.560 transport layer that provides transfer of data between end systems 0:23:25.560 --> 0:23:28.200 and is responsible for end to end recovery. Again, we'll 0:23:28.359 --> 0:23:30.680 go into this in more detail in a minute. Level 0:23:30.760 --> 0:23:33.600 three is the network layer that's the domain of things 0:23:33.600 --> 0:23:37.520 like switches and routers. Level two is the data link layer, 0:23:37.800 --> 0:23:42.720 in which all information we've been talking about the packets 0:23:42.920 --> 0:23:47.440 of information getting coded into bits. This layer technically as 0:23:47.440 --> 0:23:51.439 two sub layers. There's the Media Access control or MAC layer. 0:23:51.520 --> 0:23:54.040 If you've heard of MAC addresses, that's what this refers to. 0:23:54.600 --> 0:23:58.679 And there's the logical Link Control or l C layers, 0:23:58.680 --> 0:24:00.840