1 00:00:00,300 --> 00:00:03,040 How many layers are there in networking. 2 00:00:03,060 --> 00:00:09,260 Do we have a four layer TPP model or perhaps a five layer TPP IP model. 3 00:00:09,420 --> 00:00:13,260 Or do we have a seven layer oversight model. 4 00:00:13,260 --> 00:00:14,890 How many layers are there. 5 00:00:14,910 --> 00:00:16,590 Why do we actually care. 6 00:00:21,740 --> 00:00:28,600 Now in the previous version of the CCMA we were taught the over side model which consists of seven layers 7 00:00:28,930 --> 00:00:30,050 starting at the top. 8 00:00:30,070 --> 00:00:30,750 It's inverted. 9 00:00:30,760 --> 00:00:38,230 So from layer seven to layer one all people slipping through networking don't POS Well that's not actually 10 00:00:38,230 --> 00:00:38,850 what it is. 11 00:00:38,860 --> 00:00:45,480 It's actually application presentation session transport network data link and physical layer. 12 00:00:45,580 --> 00:00:53,050 Now that caused a lot of confusion a lot of people have debated how relevant the OSA model is in today's 13 00:00:53,050 --> 00:00:53,970 networks. 14 00:00:54,160 --> 00:00:55,510 Have a look here on Twitter. 15 00:00:56,020 --> 00:01:03,210 Rob tweeted I've got three hours to kill in an airport lounge and I'm going to discuss the OSA model. 16 00:01:03,220 --> 00:01:04,810 There's no such thing. 17 00:01:04,810 --> 00:01:08,830 What they taught you was a lie and they knew it but they didn't care. 18 00:01:09,270 --> 00:01:10,150 And that's interesting. 19 00:01:10,150 --> 00:01:14,530 People in the real world are saying that the OSA model is rubbish. 20 00:01:14,530 --> 00:01:17,830 Other people are saying well that's not true. 21 00:01:17,830 --> 00:01:19,810 The OSA model is required. 22 00:01:20,260 --> 00:01:26,140 Now Ivan is someone that I recommend that you follow on Twitter or go to his website and sign up for 23 00:01:26,140 --> 00:01:27,100 his free courses. 24 00:01:27,730 --> 00:01:30,940 Ivan is someone who doesn't mess around. 25 00:01:30,940 --> 00:01:36,430 As in he speaks what he thinks he will tell you what is true and what is not true. 26 00:01:36,430 --> 00:01:42,670 I highly recommend that you follow Ivan and perhaps you know take some of these free courses if nothing 27 00:01:42,670 --> 00:01:42,940 else. 28 00:01:42,940 --> 00:01:46,570 Follow him on Twitter and read his blog posts. 29 00:01:46,590 --> 00:01:51,160 Now if you'd really need to networking you may not understand everything that he talks about. 30 00:01:51,160 --> 00:01:54,280 Don't worry most of us struggle with some of the concepts. 31 00:01:54,370 --> 00:01:57,860 Ivan is really intelligent has years and years of experience. 32 00:01:57,970 --> 00:02:04,750 But if you want to learn from someone who has got lots of experience and can help you in your networking 33 00:02:04,750 --> 00:02:08,530 career follow him on Twitter are basically in his response. 34 00:02:08,530 --> 00:02:13,630 Ivan is saying that we do need the OSA model and if people have followed the US model life would be 35 00:02:13,630 --> 00:02:15,360 a lot simpler today. 36 00:02:15,400 --> 00:02:21,380 Now I don't want to muddy the waters just as you starting with the OSA model and the TTP IP model. 37 00:02:21,400 --> 00:02:24,700 Again I'll tell you what you need to know for the exam. 38 00:02:24,700 --> 00:02:32,230 But just note that nothing in life is as simple as it seems sometimes there are gray areas in the OSA 39 00:02:32,230 --> 00:02:37,090 model and the TCB IP model they taking what's called a protocol stack. 40 00:02:37,090 --> 00:02:42,760 In other words different protocols that do different things and they try and put it into neat layers. 41 00:02:42,760 --> 00:02:48,130 Now that's not always clear cut and it's not always possible to take protocols and put them neatly into 42 00:02:48,130 --> 00:02:54,520 individual layers because some developers have programmed the applications to do things that supposedly 43 00:02:54,520 --> 00:02:56,150 they shouldn't be doing. 44 00:02:56,200 --> 00:03:02,260 We are told in the CCN course that specific layers should talk to specific layers but that doesn't always 45 00:03:02,260 --> 00:03:03,300 happen that way. 46 00:03:03,310 --> 00:03:06,130 So moral of the story is for the real world. 47 00:03:06,130 --> 00:03:15,480 Things get more complicated and people get into these rants or discussions if you like about the OSA 48 00:03:15,520 --> 00:03:20,320 model is rubbish or we shouldn't be learning the OSA model. 49 00:03:20,320 --> 00:03:27,850 We shouldn't be learning the TTP IP model and then people code stuff from various CCN a box showing 50 00:03:27,850 --> 00:03:32,380 an original TTP IP model and an updated TTP IP model. 51 00:03:32,380 --> 00:03:37,070 And just to further complicate it here's a whole range of different models. 52 00:03:37,090 --> 00:03:41,160 Now the original model comes from RC eleven 22. 53 00:03:41,230 --> 00:03:43,190 This is a four layer model. 54 00:03:43,210 --> 00:03:49,510 We have what's called an application layer transport layer Internet layer and link layer. 55 00:03:49,510 --> 00:03:56,800 The Cisco Academy talks about Internet model being application transport into network and network interface. 56 00:03:56,800 --> 00:04:03,370 But then on wikipedia here they start quoting different books and what you'll notice we have a five 57 00:04:03,370 --> 00:04:09,670 layer TTP IP model and then a four plus one layer and then right at the end we have a seven layer over 58 00:04:09,700 --> 00:04:10,970 assigned model. 59 00:04:11,020 --> 00:04:17,050 Now the OS model once again is what was taught in previous versions of the CCMA in this version of the 60 00:04:17,050 --> 00:04:17,860 CCMA. 61 00:04:17,950 --> 00:04:26,340 They are teaching the so-called five layer TPP model which is a combination of the original RF C 11 62 00:04:26,350 --> 00:04:30,430 22 TTP IP model and the OSA models. 63 00:04:30,460 --> 00:04:33,380 So basically it's a hybrid of multiple models. 64 00:04:33,400 --> 00:04:39,280 Now the reason we have a model is we taking a complex problem and we breaking it up into smaller components 65 00:04:39,280 --> 00:04:40,690 or smaller pieces. 66 00:04:40,690 --> 00:04:42,340 This has been done for many many years. 67 00:04:42,340 --> 00:04:50,170 The Romans had a divide and conquer policy so we divide a problem into smaller parts and then we conquer 68 00:04:50,170 --> 00:04:53,190 smaller parts rather than trying to do everything in one go. 69 00:04:53,200 --> 00:04:58,990 Models are used in many places as an example if you're building a house you typically have a blueprint 70 00:04:59,020 --> 00:05:01,810 or a model of what the House is going to look like. 71 00:05:01,840 --> 00:05:08,920 So before you even dig the foundations a model is created or a blueprint is created of what the House 72 00:05:08,920 --> 00:05:10,280 is going to look like. 73 00:05:10,360 --> 00:05:16,810 It makes a lot more sense to create a blueprint of a house and then have specific people work on specific 74 00:05:16,810 --> 00:05:21,540 parts of the building and do what they are good at. 75 00:05:21,550 --> 00:05:27,270 So as an example a plumber will work on the plumbing an electrician will concentrate on the electricity 76 00:05:27,880 --> 00:05:30,790 a bricklayer will concentrate on laying the bricks. 77 00:05:30,910 --> 00:05:36,520 But they all work together to correct to the end result which is the house that you want built. 78 00:05:36,580 --> 00:05:42,970 It's going to be much easier to have a blueprint or a model that everyone works towards to build something 79 00:05:42,970 --> 00:05:47,590 rather than them just arriving on site and then saying let's bulldoze house but they don't actually 80 00:05:47,590 --> 00:05:49,090 know what the house looks like. 81 00:05:49,090 --> 00:05:53,930 You have an electrician working on the plumbing or a plumber working on bricklaying. 82 00:05:54,040 --> 00:05:56,050 That's not going to scale very well. 83 00:05:56,050 --> 00:06:04,240 So we have a model of a network and then we have specific layers or specific components or subunits 84 00:06:04,240 --> 00:06:08,770 if you like that people specialize in and concentrate on that layer. 85 00:06:08,980 --> 00:06:14,700 So manufacturer of fiber cables concentrates on building this to a specification. 86 00:06:14,740 --> 00:06:21,580 If you're a application developer you don't worry so much about the physical layer or how data is transmitted 87 00:06:21,670 --> 00:06:28,090 from let's say the US to Europe across the Atlantic using light under the ocean. 88 00:06:28,150 --> 00:06:30,240 You concentrate on building your application. 89 00:06:30,340 --> 00:06:35,890 So we have different layers in the oversight model and different people concentrate on different layers. 90 00:06:36,340 --> 00:06:41,650 Now the layers that we as networking people concentrate on are the lower four layers which in the OSA 91 00:06:41,670 --> 00:06:46,150 model are called transport network data link and physical. 92 00:06:46,150 --> 00:06:53,450 In the new version of the CCMA they are using this hybrid model where they've taken parts of the oversized 93 00:06:53,530 --> 00:06:56,430 model and added it to the TTP IP model. 94 00:06:56,430 --> 00:07:04,780 So rather than the original model of just a link layer or network interface layer we actually have what's 95 00:07:04,780 --> 00:07:10,360 called the data link layer which is called Layer 2 and the physical layer which is layer one we accounting 96 00:07:10,660 --> 00:07:19,500 upwards through the layers from layer 1 being the physical layer so ignoring all the debates and all 97 00:07:19,500 --> 00:07:25,590 the wars if you like on Twitter about which model is important and why we care about models. 98 00:07:25,590 --> 00:07:27,840 This is what you need to know. 99 00:07:28,010 --> 00:07:33,950 You need to know both the OS model and TTP IP model but concentrate on the TTP IP model. 100 00:07:34,280 --> 00:07:40,160 The OSA model which consists of the seven layers physical layer data link layer network layer transport 101 00:07:40,160 --> 00:07:47,300 layer session layer presentation layer and application layer isn't as important as the TTP IP hybrid 102 00:07:47,300 --> 00:07:48,140 model if you like. 103 00:07:48,200 --> 00:07:54,950 So a five layer TTP IP model which is more real world which has a physical layer data link layer network 104 00:07:54,950 --> 00:07:58,990 layer transport layer and a combined application layer. 105 00:07:59,030 --> 00:08:07,700 But notice we talk about Layer 7 applications because of the history of the OSA model being used. 106 00:08:08,000 --> 00:08:13,400 So notice we have layer one layer to layer three layer for those are the layers that we concentrate 107 00:08:13,400 --> 00:08:15,720 on as a networking person. 108 00:08:15,950 --> 00:08:21,710 And then we have a combined layer 5 2 Layer 7 called the application layer but we still referred to 109 00:08:21,710 --> 00:08:24,450 it as application layer. 110 00:08:24,470 --> 00:08:28,430 Now I'm gonna show you this practically using Packet Tracer but I want you to download this yourself 111 00:08:28,490 --> 00:08:29,840 and try it. 112 00:08:29,840 --> 00:08:36,230 So don't just follow me do this yourself and see if you can answer some of these questions yourself 113 00:08:36,650 --> 00:08:42,950 and see if you can understand the various layers in Packet Tracer they still have the seven layers of 114 00:08:42,950 --> 00:08:48,410 the OSA model but what you'll notice is layer five and layer six are basically ignored for for the most 115 00:08:48,410 --> 00:08:53,180 part we concentrate on the lower four layers and then layer seven the application layer.