Hi and welcome to our networking modules tutorial. In this presentation, we'll discuss both the OSI model, and the TCP IP model and then we'll compare the two. The open systems interconnection model, or the OSI model, is a conceptual model that characterizes and standardizes the communication functions between two nodes. It separates communication into seven different layers. In ascending order, these are the layers of the OSI model, physical, datalink, network, transport, session, presentation and application. This image shows the layers in descending order, along with their associated protocols and networking devices responsible for forwarding and inspecting traffic at different layers. We can also see how the traffic is encapsulated or bundled up for delivery by the different layers. The physical layer or layer one is responsible for the transfer of digital bits from the source to the destination, fiber and copper cable are examples of layer 1 technologies. Layer 1 devices include things like Knick cards, hub's, repeaters. Layer 1 traffic is delivered as bits or ones and zeros. The datalink layer or layer 2 is responsible for transmission and packages, the bits, the ones and zeros into frames. It's also responsible for the physical addressing such as Mac addresses. It can also be broken further down into two subcomponents; media access control and logical link control. Switches and bridges, for traffic at layer 2 using Mac addresses, they take the bits and package them into frames with layer 2 header allows layer 2 devices to pass the traffic. The network layer or layer three is responsible for routing packages across networks. It translates physical addresses from layer 2 into logical addresses, IP addresses, and it uses ARP, address resolution protocol to map physical addresses or MAC addresses to the logical addresses or IP addresses, routers or layer 3 devices and forward traffic based on IP addresses. Layer 3 devices package frames into packets with the layer 3 header that is added to the frame in order to forward traffic between different networks. The transport layer or layer 4 is responsible for delivering data across the network. TCP and UDP are the most common examples of layer 4 technologies. The layer 4 package are bundled into segments for TCP or data grams for UDP, this allows for reliable transmission of data between points on a network. The transport layer is the post office of the OSI model and it provides for acknowledged delivery like certified mail for TCP or unacknowledged delivery like regular mail for UDP between the two points. The session layer or layer 5 manages the initiation and teardown of network connections. They can handle multiple dynamic connections. The presentation layer or layer 6 handles two main things, syntax processing such as format conversions and encryption and decryption for the application layer. The application layer or layer 7 handles network services to end user applications. An example of this would be HTTP, which packages the data needed to send and receive web page content. When two devices or hosts are communicating with each other, they exchange information by means of that layer's protocol. The data to be transmitted at Layer 7 of the transmitting device is a PDU or protocol data unit. The PDU is passed down to the next layer, which is known as an SDU or service data unit. At the next layer down, the SDU is encapsulated with a header producing a layer 6 PDU and then is passed down to the next layer in the operations repeated again and again until it reaches a layer 1, then the data is transmitted to the receiving device. Now let's take a look at the details of this operation. At the application layer the data is encapsulated with a layer 7 header, such as a JPEG image encapsulated with an HTTP header, it's then passed to layer 6. At the presentation layer another header is added, the layer 6 header. Perhaps you're using encryption, then an SSL header would be used. At the session layer, a layer 5 header is added for session settings such as window framing. At the transport layer, a layer 4 header is added and the data is transported by segments for TCP or diagrams for UDP. The layer 4 header will contain important protocol information such as TCP 443. At the network layer, a layer 3 header is added with IP address information and transported as a packet. At the data link layer, a layer 2 header is added, this would include things such as Mac addresses. At layer 2 and FCS or frame check sequence trailer is also added to check for errors or corruption of the information. This data is forwarded as a frame and then at the physical layer of the data is forwarded as bits. At the other end, when the data is received, it is D encapsulated in reverse order. Internet protocol suite is another model to help explain network communication. It is more commonly known as the TCP IP model because the original protocols in the suite were TCP transmission control protocol and IP Internet protocol, it's also sometimes known as the department of defense model or DOD model, because the development of this networking method was funded through DARPA. The TCP IP model consists of four layers, the link layer or network access layer, the network or Internet layer, the transport layer and the application layer. These four layers map over to the seven layers of the OSI model by combining some of the layers from that model. The link layer or network access layer, sometimes also refer to as a network interface layer is the first layer. The link layer combines layer 1, layer 2 from the OSI model. The network layer or Internet layer maps to the network layer of the OSI models. Its functions include traffic, routing and control and logical or IP addressing. The transport layer maps directly to the transport layer of the OSI model. Internet protocols like TCP and UDP are part of the transport layer in both models and the application layer maps to layers 5 through 7 in the LSI model, the session presentation and application layers. In the TCP IP model, the application layer handles all of the process to process communications. This includes session establishment termination, code and data translation's encryption decryption and application protocols like HTTP, so let's take a moment to compare the two side by side. If you review both model side by side, you can see how they relate to each other. There are two models that answer the same question. Why am I able to post pictures of what I had for dinner last night and other people are able to see them? If you take an exam for networking certification, you'll need to memorize the seven layers of the OSI model. Here's a mnemonic device that I use to remember the OSI model. Just read from the bottom to the top. Please do not take sausage pizza away. Thank you for listening and I hope you enjoyed learning about the networking models.
