Hello. My name is Jerry Smith, and in. This lesson we're going to have an introduction to the TCP, IP and OSI models. Let's check it out. Anyone interested in the technology field in. Particular if you're doing any sort of sysadmin networking. And of course, cyber needs to have. An understanding of the OSI and TCPIP models. In most discussions you will see the OSI I. OSI stands for Open Systems Interconnection Model, used to explain traffic flow and how to describe issues such as the issue was a layer three problem. The OSI model is theoretical in that. It is used to visualize how networking. Occurs, but it isn't actually implemented. It was adopted by the ISO, the. International Organization for Standardization in 1984. Let's take a look at a portion of the standard. Here you can see in bullet one. Six that the intent of this standard was meant to be very broad, in. That it is a reference model used. To explain communications between computer systems, not necessarily a practical application that is to be implemented. Now let's check out the model. When visualizing traffic flow, it's important to. Know a few things. When traffic is leaving a machine, it. Flows down, and when it enters a machine, it flows upwards. Traffic does not have to originate nor. Terminate at the highest layer, but it cannot skip layers. For instance, traffic can flow from network through data link to physical and then. Back up, but it cannot skip from network to physical. The OSI is numbered from seven to one, with seven being application and one being physical. Let's look at each layer. Layer one is the physical layer, and. It'S just that it's where the machine is physically communicating across the network. That could be in the form of. Electrical signals, over ethernet light via fiber optic or radio waves via WiFi. Layer two is the data link layer. It's where Mac addresses and basic switching occurs. The traffic here is in the form of frames. Layer three is where your router lives, and IP addressing is here. Layer four is the transport layer. TCP UDP. That's transmission control protocol and user datagram protocol lives here. This is also where you find logical ports. Layer five is session. This layer maintains connections between machines. Layer six is the presentation layer. Here you'll find encryption. Layer seven is the application layer. This is where you interact with the machine. Chrome, Firefox, et cetera, live here. In terms of on the job, it. Seems like layers one through four are. The most often discussed. To memorize the OSI model, there are. Two popular mnemonics that will help you remember. The first letter of each layer from. Bottom to top is Please do not. Throw sausage pizza away from the top. Down and not quite as relevant of. A reference is all people seem to need data processing. Now let's take a look at the TCP IP model. TCP is Transmission Control Protocol and IP is Internet Protocol. The TCP IP model was developed by the IETF. That's Internet Engineering Task force in 1981. Actually predating the OSI model. This is the original standard, and here. You can see the rudimentary four layer model. What I find most notable is the line that references the Internet datagram. It states that it offers a method for providing addresses on multiple networks that set the stage for a model of. Internet traffic that is still in use. Today over 40 years later. Here's the model. Notice it only has four layers, but let's look at each one. Layer one is Network Access and it. Handles physical access, Mac addresses, and basic switching. It matches up to OSI layers one and two. Layer two is Internet and is responsible. For routing and IP addresses and matches. Up to the OSI at layer three. Layer three is Transport, handles Ports and. It matches up to OSI layer four. Layer four is Application and handles everything dealing with software. And as you can see, it matches. Up to OSI layers five through seven. Let's look at the models side by side. Here you can see how they match up. By understanding these models, you can troubleshoot. Issues much more quickly, and as a. Bonus, they make great interview questions. Stay tuned for the next lesson where. We will have an introduction to the TCP Dump application. Thanks for watching. If.