The Building Blocks of Networking

0:00The question of the day, what is networking? Well, that's a great question. And that's what this course is all about. So what is networking? Well, networking is the interconnecting of devices. So we could have maybe a computer here, a desktop, and you could have a laptop computer over here. There we go, they look kind of similar. You might have your smartphone over here that you're working with, or it could be a larger implementation of that, a tablet.

0:31But either way, we have all these devices, including things like servers, that need to communicate. These are compute devices. And in order to share information, they need to be able to send it to each other. And they do so over a computer network. So that's the idea of networking. It allows these compute devices to communicate. And today we take networking for granted, basically because most of us have lived with it for so long. But I remember a time when, well, this wasn't there.

1:02All we had was standalone devices. So with that being said, let's talk about rules and standards when it comes to networking. Now, as you can imagine, we've got all these devices out there that are wanting to communicate with each other. And in order to do so, they're going to need rules and standards, just like as people when we talk to each other, like we've got the fellow over here and over here. And if they want to talk, well, they need to be able to speak the same language or communicate in some form or fashion.

1:35If they're speaking a language, there are rules when it comes to languages. And in order for people to communicate, they need to follow those language rules. And the same thing is true for networking. There are rules and standards that have to be followed. We don't want the wild, wild, west happening on our networks, because then our communications will be very poor. And it's just not going to be acceptable. We need to follow those rules and standards so that our networking works as we expect it to. And we'll be talking about these rules and standards throughout the course.

2:08Well, do we need equipment for networking to happen? The answer is absolutely yes. We sure do. We need devices to allow our compute devices to communicate with each other. So if we've got these devices over here, well, in order to communicate over a network, they need something called a network adapter or a network interface card. And we're going to talk about this more in the next nugget. But the idea is you need something on here that's going to allow these devices to either wirelessly communicate to a network or be plugged in to a network via a wire cable of some sort.

2:48So yeah, we need equipment. We need network adapters. And if we're going to talk to devices outside of our network, well, we're going to need to have some sort of gateway off of the network. And this gateway is oftentimes going to be a router. And that's going to allow us to get off network. And on network, when we're wired, we're going to be using switches in order to allow traffic to pass to other wired and wireless devices.

3:19So this is kind of the idea that, yeah, we need equipment. And we're going to be talking about various types of equipment and some commands that we can use on some types of equipment throughout the course. All right, here's something for you to think about. Networking, well, it's like the postal system. And that's because every location that is going to have mail delivered to it or data on a network, it's going to need a valid address so that it can receive and send information.

3:52Just like if we create a letter here, we're going to write a letter on the front of that letter, we're going to need to put a destination address on here. And we're going to put our source address on the top of the envelope there so that our postal system will know where to route that to, where to send it to. So the idea is, we've got a mailbox down here. If we want to communicate via the postal system, we need to have valid addresses. Well, the same thing is true for a network.

4:23You need to have valid addresses as well. And we're going to start talking about those addresses in the next nugget. So when we send a letter, it goes to our local post office. So we're going to drop it off there. And then it gets sent out via mail trucks wherever it's going to go. And it gets delivered to the next post office where then it gets delivered via truck or mail carrier to the final destination over here, the mailbox. Well, when it comes to networking, it's very similar.

4:54When we send out data, it's going to go to something to be delivered. It could be a switch, it could go through a router, it could go through multiple devices. But the idea is then it's going to be transmitted, just like a mail truck transmits mail. Well, we're going to be using wireless to transmit data or wired, either way. But it's going to get transmitted off to somewhere else where that data is going to be then forwarded on and delivered. So the idea of networking being like the postal system is actually pretty cool if you think about it.

5:29And it will help you to understand it a little bit more as we go through networking if you have something to reference it. All right, so now that we're all on the same page about what networking is, let's go ahead and get started on our journey to the C, C, S, T or Cisco Certified Support Technician. In networking. And we're going to kick this off in the next night by digging into networking addresses. And there's more than one type, believe it or not. So I'll see you there shortly.

0:00So let's talk about network addressing. So when you're at your house, I'm going to go to the house over here, there we go. And you're sitting there waiting for your Amazon delivery to get to you. Here it comes right down the road and it's going to deliver your package. We'll even put a little bow on it there. How about that? So you're going to get your package delivered. Well, in order to receive that package, you need something. You need an address so that the Amazon driver, delivery person will know where to go to deliver your package.

0:32Well, the same is true on a network. We've got to have addresses. And in order to connect to a network, to even be part of it, we need something called a network interface card or a NIC, also known as a network adapter. And this is a drawing of one over here on the right. And this is your standard network adapter that you would see in a computer. And actually from the outside, you're just going to see a port where you can plug a cable into, or you might have an antenna that sticks off of here, something like this, so that it could be a wireless network adapter.

1:10So you could have wired or wireless, but think of your network adapter as you're on ramp to the digital highway. That's how you're going to gain access into the network. You need a network adapter or network interface card. Okay. And that's going to be in all your devices, your smartphones, tablets, servers, workstations, switches, routers, wireless access points, all of them have network interface cards in them. So again, that's how we're going to gain access onto the network.

1:41Now once we're on the network, we're dealing with addresses. And we're going to deal with two different types of addresses. The first one is called a MAC address. And this MAC stands for media access control. And it is a 48-bit hexadecimal address. And this is an example of one right over here. And we see here hexadecimal, that means that we are using numbers 0 through 9 and letters A through F.

2:15There you go. And it is 48 bits, so you'll see there are actually six fields here. We've got one, two, three, four, five, and six. That means each representation in the field is eight bits in length, which is pretty interesting. Now let's talk about what these values mean here. Well, the first three fields here are known as the OUI.

2:46And the OUI is the organizationally unique identifier. And again, that is the OUI. Now what is the OUI? Well, this is a unique identifier that identifies who the maker or manufacturer of that network card is. And that's actually assigned by the IEEE. And this is the Institute of Electrical and Electronic Engineers. And it's a group that manages the distribution of OUI.

3:17So this first section here, the first half of the address, you can actually go online and Google OUI Lookup. And then you can paste in those first three blocks of data there. And it'll tell you who the manufacturer of the card is. Now you might be wondering, well, what about the last three blocks here? Well, those act as more of a serial number. The manufacturer puts numbers in there so that they end up as part of the address.

3:47So you have your OUI plus your serial number part, and that gives you your full MAC address. Now the MAC address is known as a hardware address. And that's because that MAC address is actually hard-coded in our network interface cards that we just talked about. So on there, you have processing power and you have memory and various other components. And your hardware address or your MAC address is hard-coded into the memory or firmware of your network interface card.

4:24And that's why it's called a hardware address. And every device that's out there that's on the network has a hardware address on it. And this is things from your phones, your routers and switches and access point and computers and servers and tablets and anything that communicates on a network is going to have a MAC address. Now the thing about your MAC addresses, they're used to communicate on your local network. Okay, so they are local to your network.

4:55Once your data leaves your network and goes somewhere else, well, that MAC address gets changed. As it goes through various other networks. So that's something to keep in mind. So that's your MAC addresses. Next up, the other type of address we're going to talk about are IP addresses. And here's an example of an IP address right here. And this is known as the dotted decimal notation.

5:25Now what does that mean? It simply means that we have decimal meaning numbers and we have dots in there. And that's what we see, dots and numbers. Now I say this because when we think about how devices communicate over network , well, they are doing so using binary. Meaning ones and zeros. So if we were to take a look at this IP address right here in its binary format , well, it's going to look like this. Yeah, that is quite a long address.

5:56Now these addresses are 32 bits in length. So if you count these numbers down here, you'll find there are 32 numbers. And these addresses are used to communicate not only on your local network, but also to other networks. So the IP addresses we use for end to end communications. Whereas when we talked about the MAC address, it's really only used for communications on your local network.

6:30But IP addresses, hey, those are end to end communications from your sender to your receiver. And we're going to get much deeper into IP addresses and subnetting and all those things. Right now we're just kind of getting a feel for the lay of the land. All right, so those are two types of addresses, our physical MAC address and our logical IP address. And it is a logical address because we configure it within the operating system that we are working with.

7:03So yeah, these are not hard coded into any hardware like the MAC address was. These are actually configured within our operating system. So that's the basics of network addressing. In the next nugget, we're going to jump in and start talking about the TCP/IP model. So I'll see you there shortly.

0:00The TCP/IP model. Now, earlier we discussed the need for rules and standards when it comes to networking, so that we don't have the wild, wild west of network full of confusion. We have a nice and orderly network. That's right, that's what we are looking for here. And when it comes to networking, as you can imagine, there's lots of moving parts out there and we really need a way to kind of organize all of those things to make it easier to manage. And troubleshoot when something breaks.

0:31And this leads us to our TCP/IP model. And this is a way for us to kind of organize all those moving networking pieces . And it really is kind of a framework for understanding and organizing all of the moving parts of networking. So the TCP/IP model was created by the US Department of Defense, that is the DOD, and it was created in the 1960s.

1:04And it has four sections used to group networking activities together. Those four sections are, as you can see, application layer, transport layer, internet layer, and network access layer, all of these. So let's talk about what these are individually or what they do, starting at the bottom. So down here we have our network access layer. And as you can imagine, this provides network access to all of our devices. So this is the layer that has the cables plugging into it.

1:38So if you think about this, our network interface card resides here within the network access layer, which also means our MAC addresses also reside here because remember they are part of the network adapter. They're hard coded on there. We also have our cables in this layer or wireless. If we're using wireless communications, all of these things reside down here at this network access layer. And this is where all of our bits are sent out across the network, like so.

2:12So that is network access layer of the TCP/IP model. So if you think about it, this is kind of our on-ramp to our digital highway. All right, so that's a network access layer. Let's take a look at the next layer. And that would be our internet layer. Now this is where our IP addresses reside. Remember we talked about the IP addresses and how they are a 32-bit IP address? And they're used for our end-to-end communications.

2:43And this is also where routing takes place. We had talked about different hardware and the idea that router is one type of hardware that we use. And a router is actually a gateway off of our network. It helps us to go to other networks, a router does. And what happens is the router looks at IP addresses and according to its configurations, will send them to a neighboring device, like another router, or it could be a local switch.

3:16Or it could be directly to the destination where that data is headed to. So that is our internet layer moving on. Next up is our transport layer. Now this layer is responsible for establishing communications between devices and managing those communications. So really it establishes and manages communication sessions. And this is actually the layer at which we see TCP and UDP reside.

3:55And that TCP is the same. Famous TCP of the dynamic duo TCP IP that you've probably seen somewhere written down or being referenced as TCP IP. Well we talked about the IP address in the last nugget. Well now we're talking about the TCP portion of that dynamic duo TCP IP. Now TCP is known as a connection oriented protocol.

4:26And a protocol is simply a set of rules used to communicate. And connection oriented means that it makes sure that there's someone at the destination who's willing to accept that traffic or data before it sends it. So what happens is when you're using TCP IP, your TCP is going to go over to your destination, which will be this right here. And it's going to say hey, would you like to communicate? Can I send you some data?

4:57And if the answer is yes, well then it's going to use its IP address to communicate end to end and send data. But if the answer is no, or there's no response, well then what happens is well communication simply doesn't happen. And that's the idea of a connection oriented protocol. It wants to make sure somebody's there to receive the traffic that's coming across the network. On the flip side of that is UDP.

5:29Let's talk about UDP. UDP is a connection less communications protocol. And that means that in this instance, if we're using UDP and we have a destination over here, well what's going to happen is this node is simply going to transmit the UDP data to the destination without checking to see if that destination is willing to accept the data. So UDP is more of a send and forget type of communications.

6:01It's not going to be making sure someone is there to receive it like TCP. Now why on earth would you ever want to use UDP versus TCP? If TCP is going to make sure that my data gets there, somebody's there to receive it and it's going to get transmitted and received versus UDP, why would everyone to use UDP? Well, there are a couple of shining examples where UDP works better. Now because TCP does this communication and there's a checking back and forth that happens and we're going to go through that a little later on, this takes more time.

6:38Okay. When using TCP communications, UDP is more of a slim communication protocol, meaning it doesn't take as much time. There's not as much going on. It's very simplified in compared to TCP. So UDP is actually faster. And when we're streaming data, think of like a streaming of a movie, okay? Or could be online gaming, which many of you probably are familiar with.

7:12If you're using a service like a streaming service or online gaming, just think about this. If you're watching a movie and the screen pixelates a little bit because the little data was lost and then the movie continues, right? Absolutely. It happens all the time. Pretty normal. Do you want that data back that was lost where that pixelation happened? Well, if you got it back, it would cause you to see the old data or that scene of that movie out of order.

7:42So if you're watching, let's say, a police chase in a movie and they're chasing the bad guy down the road and then you get a little pixelation or some data is lost. But then the movie continues and the police have stopped the bad guy and they have him out and they're arresting him, putting handcuffs on him. Do you want that data that you lost back at this point? Because if you did get it back, then your scene here would be interrupted with data or images from a previous scene and it would be really weird, right?

8:18And the same thing for online gaming. If you're playing a game, you don't want to get lost data back while you're playing the game because it's going to cause you visual interference. It's just not good. We don't want that. And that's where UDP shines is when we're dealing with real-time data. All right, so that is our transport layer. All right, we got one more to go. And that is our application layer. And as you can imagine, this is where our applications reside and our application data, as you can imagine.

8:54And this is where we have our networking happening down here. And up here we have our applications. So we're going to have translations taking place at this layer because our data coming up here is in a network format, but it needs to be translated into some other type of format that your application is going to use. Is it an mp4 format? I don't know. Is it a JPEG format? Is it some other type of format?

9:26So your formatting is going to happen there as well as your encryption. So if you have any encryption that's being used, the encryption and decryption takes place at this application layer. So really, it's where your applications are sharing data with the network and the network is sharing data with your application. So you got your translation and your formatting and all of that wonderful stuff taking place right there. So this is our TCP/IP model. And again, this is more of a framework than a standard.

9:58And it's really there to help us to organize all of the going ons of the networking world that we deal with here. Now, this does really focus on TCP/IP since it's a TCP/IP model, but there's lots of other protocols out there as well. And a little later on, we're going to talk about the OSI model, which is another model, but it's more widely used for things other than TCP/IP. Yes, it's used for TCP/IP as well, but it also represents other protocols.

10:30So we're going to get into that a little bit later. But next up, we're going to dive into TCP a little more. We talked about comparing TCP as a connection-oriented protocol and UDP being connection less and how they were different. And we talked about when you'd want to use UDP when we're talking about real- time data and such. But TCP is a little more complicated. So we're going to have a nugget just on TCP. And that's what we're going to talk about in the next nugget. So I'll see you there shortly.

0:00In this nugget, we're going to be talking about the TCP 3-way handshake and something called sockets, but we're going to start off with fragmentation. Okay, and this is the breaking up of data as it's sent out across the network. So think of your network data as a train, because if we have a device here, say your computer and you're connected to the network, if you go and download a file, let's say you download a 10 megabyte file from the Internet.

0:36Okay, well, there's something called an MTU right there. Okay, and this stands for maximum transmission unit. And it defines how big each section of your data can be. So again, I'm referencing your network data as a train. Okay, and there's a reason for that. Now remember, you're over here downloading this 10 megabyte file. Well, the way it works on a network is you're not going to get one piece of data that is 10 megabytes in size.

1:13That's just not how it works. What actually happens is that data is broken down into several smaller pieces and it's sent out over the network, and that is known as fragmentation. So we have this big piece of data here that is 10 megabytes in size. Well, MTU defines how big each piece of data can be as it goes across the network.

1:45And Ethernet, which is a standard that we use to send data across a network, that Ethernet defines the default MTU size as 1500 bytes. Okay, so that means we would take this 10 megabytes and divide that by 1500 bytes, and that comes out to 6,667 as the answer to that.

2:18Okay, so that means our train is going to be 6,667 train cars long. And again, the process of breaking up these large chunks of data into smaller pieces before sending them across the network is known as fragmentation. Now, these chunks of data that we're sending out, we're going to refer to them as packets for now, and you'll see that data at different layers of different models is called different things.

2:49So we're just going to call them packets for now. So if we have 6,667 packets as part of our 10 megabyte download, well, they're not actually hooked together like a train. They're simply sent out, and they each find their own way to the destination. And as you could imagine, they get there out of order a lot of times. It's just the way it happens. So what TCP does is when it sends these out, it includes a sequence number.

3:20So the first chunk of data will have a sequence number of one, and then we have two and three, and all the way up to 6,667. All of that, okay? And that way, when it arrives at this destination over here, the destination can make sure to put them all back in order before sending them up the rest of the networking stack, going through the different layers all the way up to the application. So this process of fragmentation happens within networking, and it's the sequence numbers that allows us to make sure, well, our devices to make sure, that they all get put back into the correct order.

4:01So that is fragmentation. All right, now let's talk about TCP and its three-way handshake. Now remember, TCP is a connection-oriented protocol. So it's going to make sure that there is a device at the destination willing to accept the traffic before it sends it out. Now, how does this happen? Well, it does this via the famous three-way handshake.

4:31So we got Bob over here is the client, and Lois over here is the server, and Bob wants to go out and communicate with the server, okay? So the way this works is there are three steps in here, part of this handshake. First off, Bob is going to start the communication process, and Bob is going to send across something called a TCP-CIN, okay, just like that, S-Y-N, and that stands for synchronize.

5:02So it's going to send that CIN across looking for a response, but it doesn't only send that CIN. Remember, we said that TCP uses something else as well, and that was a sequence number. So let's say here we have sequence number five, okay, as this going across. Well, if the server, Lois, decides you know what, I would like to communicate with Bob. Well then, she's going to send, or her device will send, back a TCP-CIN-AC, just like that, okay?

5:45And that is acknowledging that she received the CIN and would like to communicate. Now, that's not the only thing being sent, right? Oh, absolutely, there's got to be a sequence number in there. So let's put her sequence number in here, and let's say this is sequence number 103, okay? But guess what? That's not the only thing going to be sent. There's also an additional ACK. So we're going to put an ACK in here, and we're going to say number six.

6:16Now, what does that mean? What it means is she is acknowledging that she received sequence number five. So this acknowledgement is actually a plus one, or one more, than the sequence number, this one right here, that she received. So as the sequence numbers come across, the devices will acknowledge with this type of ACK here, that it received that previous sequence number.

6:50So that ACK there is acknowledging receipt of sequence number five. Okay? And that's how TCP makes sure that all the data makes it to its endpoint. Because if she did not acknowledge this five, then Bob's client over here would retransmit sequence number five. Okay? So that is the second part of the three-way handshake. And lastly, Bob's device will send across a TCP ACK.

7:26Just like that. It's a final acknowledgement saying, "Okay, thanks Lois for wanting to communicate with me. I'm now going to start sending you some data." But of course, what comes along with this? Well, we've got to send a sequence number here. So this is going to be sequence number six, since we used five up here. The next one is going to be six. Okay? And then we're also going to acknowledge that we received Lois' 103. And how are we going to do that?

7:57Well, we're going to act for 104. So we'll put down here acknowledgement number 104. That means that I received that 103, me being Bob over here. And that's the TCP three-way handshake. So it starts with a sin. Then we get a sin ACK in response, and we send out a final ACK. Those are the three steps right there in the TCP three-way handshake. And the sequence numbers are also in there.

8:27And we are also acknowledging those sequence numbers as data goes back and forth. That is done because TCBB, being connection oriented, wants to make sure that all the data makes it across. So if, let's say Bob sends some data over to Lois, and she never gets it, she's not going to send one of these acts back saying that she received it. And that means I'm then going to retransmit that data. So that is your TCP three-way handshake, and how sequence and acknowledgments work to ensure all the data gets across the network to its destination.

0:00All right, next up, sockets. That's right, we're gonna be talking about ports and sockets here and what they are. Now, we have talked about TCP and UDP, how TCP is a connection oriented protocol, UDP is connection less, okay. Well, TCP and UDP use something called ports, okay. And when we talk about a socket, a socket is an IP address, so we could put 1.2168.10.55, that's an IP address, followed by a colon and a port number.

0:38This right here is a socket, okay. So it's an IP address, which is the address of a system somewhere, a device. And then we also are adding here a port number. And it could be TCP port number or a UDP port number. So what are these port numbers that you talk about, Bob? (chuckles) Well, port numbers are ID numbers for services. And these services run on devices.

1:10Now, if you've ever gone to a website, which I know you have, you have visited a web server. And when it comes to web traffic, HTTP protocol is what we're using there, that actually uses TCP port 80, just like that, okay. And there are many, many, many, many, many, many, many, many ports out there, actually. Let me change colors here. There are 65,535 ports in all. And yes, that is a whole lot.

1:44Now, the first 1024 ports, that is ports zero through 1023, are known as well known ports. Okay, so these are kind of predefined reserved ports, if you will. And these are defined by IANA, I-A-N-A. And IANA is the internet assigned numbers authority. And that's an organization. And one of their duties is defining those well-known ports.

2:17So let's talk about some of these common ports. Well, we looked at TCP port 80, and that is used for, of course, HTTP over here. But if we do TCP port 443, that is HTTPS. So that is our secure web traffic. And 25, so if we do TCP port 25, that's your SMTP protocol. All right, or your SMTP service, and that's for your simple mail transfer protocol.

2:50So it's for email. Now, there are a lot of ports, as we see here. I'm not going to go through all of them, but we're going to be seeing them throughout this course, and we'll be discussing more of them as we go along. This is kind of get you in the mindset of understanding that ports are how we gain access into services that are running on devices. Now, another example I'd like to use is we have an IP address 192.168.10.55, okay?

3:24And if we were to go to that address here and communicate with it, think of gaining access into a building. And an example I'd like to use is the movie, The Matrix, where the character is in this long hallway, something like this, and it has all these doors just in the hallway, just like this. So when you gain access to a system and you're able to communicate with it, each one of these doors is associated with a port number.

3:58And that port number leads to a specific service, like our web service or email service. And that's where the sockets come into play here. We have our IP address, so we know what client we're trying to communicate with, but what service are we trying to communicate ? What protocol is that? And that's where that port number comes into play. And that's where the sockets really allow you to communicate directly with a specific service on a certain protocol. So that is our sockets and our TCP and UDP ports.

4:31In the next nugget, we're going to look at another type of reference model for networking, and this one's called the OSI model. So I'll see you there shortly.

0:00Welcome to the OSI model and the OSI model is another type of reference architecture or framework that we can use to organize and manage network communications. Now the OSI model stands for Open System Interconnect. That is the OSI. Okay and this is managed by ISO and that's the organization for international standards. Okay so that is who actually owns the OSI and manages it but it was originally invented by this French software engineer named Hubert Zimmerman. Just a little FYI in case you ever come across a networking jeopardy question like that. So let's see what this OSI model is all about and we're going to see here that there are seven layers in the OSI and we're gonna start down here at the bottom at the physical layers. Let's get started. Here we go physical. Our physical layer is where the physical connectivity happens to the network. So here at the physical layer we have our

1:17cabling. So it's our cables or wireless. Okay and at this layer data is known as bits. Okay that's our ones and zeros our bits are being sent out across our physical network. Now let's talk about some hardware as well. Okay so when we have hardware on our network and we're gonna actually talk about some different types of hardware in this skill and where it resides in the OSI model. So at the physical layer we have our cabling or wireless and that's some hardware right absolutely. Now something else that resides at the physical layer is our network interface card. Now the network interface card is a little tricky because it actually resides at the physical layer and the data link layer which we'll see next and that's because our NIC is where our cables plug into or our wireless signals are sent and received and that's why it resides at that layer.

2:24Okay so that's our physical layer just think of that as your physical network. What things touch and that's your physical layer. Next up moving up we have our data link layer and as we said our network interface cards reside at this layer as well and that's because this is where our MAC addresses reside. Okay and the data link layer is actually split into two sub layers. One is the MAC two is something called LLC and this is our logical link control and this is the mechanism that helps to manage communication. All right and when we're working at this layer data, let me change colors here, data is known as frames.

3:15So we see that data goes by different names depending on which layer that you're working with because if we go back to our physical layer down here we saw that data is just simply known as bits but when we get up to the data link layer we see that our data is known as frames and this is where our network interface card resides but remember our NIC also resides over here on our physical layer and that's because that's where the cables plug into and then as we go back to our data link layer our MAC addresses reside at the data link layer and our MAC addresses are also hard-coded into our network interface card. And one more thing I want to talk about at the data link layer we know that as far as hardware goes at the data link layer we have our network interface card remember that resides at both our data link layer and the physical layer but we also have switches. So our switches that we plug into on our network those reside at the data link layer because switches use MAC addresses to make switching decisions and access points. Those wireless should put that on there wireless access

4:31points those are also at the data link layer so there you go that is the hardware at the data link layer moving on up next up is our network layer there we go and at the network layer this is where our IP addresses reside okay that's very important and this is where routers reside that's our physical network appliance routers or it could be a virtual router as well but either way routers reside at layer 3 because routers provide us routing services and routing is based on IP addresses so these really go together like peanut butter and jelly. Now you might be wondering hey what is data known as at this layer well data at the network layer is known as packets there you go packets it is. Alright super now I'm to the next one on to our transport layer now transport layer this is where TCP and UDP reside so that means because we

5:49talked about TCP and UDP having ports this is where our port numbers reside absolutely and this is where our TCP 3-way handshake happens because that's where TCP resides and of course you might be wondering well what is data known as well at this layer data is known as segments and another thing is since we're using TCP at this layer this layer ensures that the data packets arrive accurately and it ensures that they are put in the correct sequence so that they can be sent right up the rest of the OSI. Alright next up is our session layer now the session layer manages end-to-end communication so it's responsible for going through the process of setting up a communication session and then maintaining that session and then tearing down that session when communications is finished okay so the session is all about managing the

7:10communication session between devices and data at this layer is simply known as data that's right for the rest of the way up the OSI data is simply known as data pretty straightforward there next up is our presentation this is where data translation and formatting occurs so this is we're going to see things like your mp4 and jpeg and all your other types of different file formats and this layer also handles encryption and decryption so that is your presentation layer and then lastly we're on to our application layer and this is where application protocols reside so those protocols that we talked about earlier we talked about HTTP and HTTPS and SMTP for email all those are going to reside up here at the top of the application this is where we have file sharing taking place this is where we access databases so database access this is where messaging takes place and this kind of basically injects data into our

8:29apps and that's the application layer all right so that is the OSI model and it's seven layers and what resides at each layer and kind of how things work and if you're wondering how you can remember the order of the OSI's seven layers I've got a couple of mnemonics for you the first one is please do not throw sausage pizza away and that is for your physical data link network transport session presentation and application layers so please do not throw sausage pizza away and if you don't like that one got a second one for you and this one is all people seem to need data processing and this one goes from the top down we have application presentation session transport network data link and physical so there you go a couple of mnemonics to help you remember the seven layers of the OSI model and now that we've seen this OSI we know what it is in the next night we're gonna see the OSI in action so see you there shortly

0:00All right, let's see the OSI in action. So over here we have Bob, and Bob is gonna send some data over here to Lois at the server. So Bob uses whatever application he's using, this could be an email, it could be a file transfer, whatever it might be. He wants to send something over to the server, so he does so in his application of choice, which then generates the application layer data. Okay, and as that data goes down the OSI, we're gonna follow it throughout its journey and then across the network over to Lois and back up the OSI on Lois's side.

0:43So right now we have our data and it's in an application format, so put app format, there we go, whatever that application is, and then that data is passed down to the presentation layer and here is where that data is formatted into binary. Okay, 'cause that's the computer speak, that's where we're gonna transmit that data in, then that data gets passed down to our session layer.

1:16Okay, and at the session layer, we know that the session layer's going to go ahead and set up end-to-end communications with Lois, or her device that is, and then at that point, that data is handed down to the transport layer and once it gets to the transport layer, if that application's using TCP, so let's say it is, it's going to then do the TCP three-way handshake, excellent, all right, and it's actually going to do something called adding a header.

1:54So what it's going to do is add a header to the data and it's gonna provide some TCP information. So the way this looks is we have our original data here, this is the data that came from the application. So here we're going to add what's called the header and this is going to contain TCP information there. Okay, and then at that point, the data is passed down to the network layer and here is where the IP address resides and we're gonna see a routing take place and so on and so forth, but what happens is we get a network layer header added in, so there we have our network, here's our TCP and then here's the original data, so let's fill this in.

2:38So here we have network-related information, this is TCP and this is the original data. So you see we're adding headers on here and adding of headers is known as encapsulation, okay? Super, so then as the data is passed down to the data link layer, here we're going to add a data link header, we still have our other information here, so let's put in here, we'll say Mac for like Mac address, which relies at the data link layer and we have our net information for a network layer, TCP and our original data, all right, super.

3:22And so here at the data link layer, the device is gonna look at the Mac address, it's going to be deciding on what to do with that, is it on network or off network, it's gonna pass that down to the physical layer and here's where we end up converting all of this information into ones and zeros and we're sending them out on either the cable or over wireless. So that is the process of encapsulation, as that original app data is going down the OSIMO, then the exact opposite happens.

3:57Once it gets over here across the network to lowest in the server, well that data is received, those ones and zeros here at the physical layer and then it's passed up to the data link layer. And here we have, let me draw over here the encapsulated data, we have here, there we go, just like that, our two, three, original data, but we also have our Mac headers, for layer two header, we have our network layer header, we have our TCP header here, and then we have the original data.

4:36So what happens here is the layer two data link layer will take a look at this information in the Mac header and then process that data and send it up to the network layer. Now at the network layer, we're not gonna have that Mac header anymore, it's just going to be our network information here, our TCP and the original data, because the data link layer removed this Mac header. And so then at this point, the network layer is going to receive this data, it's gonna verify the network information here in that header that we just talked about, and it's gonna strip that off and then pass it up to the transport layer.

5:16At the transport layer, as you can imagine, the same thing's gonna happen here, we have our TCP header and then our original data. Okay, the transport layer is going to go ahead and strip off this after it reads that information and decides what to do with it, because at this layer, we're gonna have TCP information, including the port number. Remember we talked about ports earlier and sockets, well that port number's going to reside in that TCP header down here. Okay, and so it's gonna strip that off and it's gonna send that data right up to the session layer over here, we have our regular data, and the session layer again is managing the end-to-end communications, this will then be passed up to the presentation layer.

5:58And here the data that we have, which is binary, it's gonna be converted into formats for an application, and then passed up to the apps themselves. So the process of removing the headers, like we see here, is called decapsulation. So here we see how encapsulation and decapsulation happens as data goes through the various layers of the OSI model. So this is the OSI in action, so in the last night we talked about what the OSI was, what happened at each layer, what equipment was at each layer, what data was referred to as each layer, but here we see that as data goes through these layers, going down and then back up at the remote side, that some of the layers, actually starting here with the transport layer, add a header.

6:46So that's our transport network and data link layer, I'll add a little bit of extra data to our packet. So this is information related to each layer that will help ensure that that data is accounted for and received by the correct endpoint and processed correctly as well. And that process is encapsulation, and then at the other end, we decapsulate it, we pull those headers off and use that information to make sure that that data is processed correctly. So there you go, the OSI model in action.

7:16And that wraps up this skill. So next up, we're going to do a validation, got some review questions to see just how well you retain this information. So I'll see you in the validation shortly.

0:00All right, here we are in our validation. So we've got a few review questions that we're going to go through and see just how well we retain this information. So question one here, it says place the four layers of the TCP/IP model in the correct order from bottom to top. So this means from the bottom will be number one. So what's at the bottom of the TCP/IP model? If you remember, it was network access. So network access should be number one that's at the bottom.

0:32Okay, so what came after network access going up? Because this is where we access the network. Well we need an IP address to communicate over the internet. So this is actually number two there. Because we started with network access, where we gain access into the network. But then as we go up, we needed an IP address that happened to reside at the internet layer. And then we need some communications and that's the transport layers. That's number three. And that leaves the application layer all the way at the top as number four.

1:05So that is your answer there. Now let's move on to question number two. Ooh, here we go. Place the seven layers of the OSI model in the correct order from bottom to top . All right, so let's see here. What was at the bottom? If you remember, we had some new monics to help us remember this. I prefer, please do not throw sausage pizza away. That starts at the bottom. So P was for physical. So physical is number one. So that was our physical. If we do, please do not, well the do is for data link.

1:38So that's number two. And the not is for network, which is layer three. There we go. Then we come through throw sausage pizza away. So the T and throw is for transport. That's number four. And then we have our image. It's our session. That's for doing our Indian communications management. That's number five. And then pizza. Well, we already know that this P is for physical as at the bottom. So this P must be presentation. That's right. And then lastly, application is at the top.

2:09So that's your, please do not throw sausage pizza away. OSI model layers in order from top to bottom. All right, question number three. What type of address resides at the data link layer that OSI model? So if you think of the data link, remember the network of data link. The data link layer is a data link layer. And it's a data link layer because a certain type of address is hard coded onto the network interface card. And that's your hardware address or MAC address. There you go. The MAC address resides at the data link layer of the OSI model. Moving on to number four.

2:41What does TCP use to ensure packets are put back into the correct order when received by the destination? So remember we talked about those getting broken down via the process of fragmentation into many little packets that go across the network. And how did TCP make sure they were able to be put back in order? It used the sequence number. That is correct. Excellent.

3:11Moving on to number five. Final question. UDP is a connection oriented protocol and TCP is connection less. Is that true or false? That's right. TCP is connection oriented. That's where that three-way handshake comes into play. UDP is connection less. So those are our five review questions as part of our validation challenge. I hope this has been informative for you. And I'd like to thank you for viewing.