![]() If you can understand the OSI model and its layers, you can also then understand which protocols and devices can interoperate with each other when new technologies are developed and explained. While some people may argue that the OSI model is obsolete (due to its conceptual nature) and less important than the four layers of the TCP/IP model, Kumar says that “it is difficult to read about networking technology today without seeing references to the OSI model and its layers, because the model’s structure helps to frame discussions of protocols and contrast various technologies.” “The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools.” In a Quora post asking about the purpose of the OSI model, Vikram Kumar answered this way: After that, you hear about the OSI model when vendors are making pitches about which layers their products work with. Most people in IT will likely need to know about the different layers when they’re going for their certifications, much like a civics student needs to learn about the three branches of the US government. When a networking problem occurs, many networking pros go right to the physical layer to check that all of the cables are properly connected and that the power plug hasn’t been pulled from the router, switch or computer, for example. This can include everything from the cable type, radio frequency link (as in a Wi-Fi network), as well as the layout of pins, voltages, and other physical requirements. ![]() Layer 1 - PhysicalĪt the bottom of our OSI model we have the Physical Layer, which represents the electrical and physical representation of the system. Some switches also operate at Layer 3 in order to support virtual LANs that may span more than one switch subnet, which requires routing capabilities. In the networking world, most switches operate at Layer 2. Two sublayers exist here as well-the Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The Data Link Layer provides node-to-node data transfer (between two directly connected nodes), and also handles error correction from the physical layer. Routers at this layer help do this efficiently. You might know that your Boston computer wants to connect to a server in California, but there are millions of different paths to take. In its most basic sense, this layer is responsible for packet forwarding, including routing through different routers. Here at the Network Layer is where you’ll find most of the router functionality that most networking professionals care about and love. Functions at this layer involve setup, coordination (how long should a system wait for a response, for example) and termination between the applications at each end of the session. When two computers or other networked devices need to speak with one another, a session needs to be created, and this is done at the Session Layer. A good example of this is encryption and decryption of data for secure transmission this happens at Layer 6. In other words, the layer “presents” data for the application or the network. In general, it represents the preparation or translation of application format to network format, or from network formatting to application format. The Presentation Layer represents the area that is independent of data representation at the application layer. Web browsers (Google Chrome, Firefox, Safari, etc.) TelNet, and FTP, are examples of communications that rely on Layer 7. ![]() Instead the layer facilitates communication through lower layers in order to establish connections with applications at the other end. Oddly enough, applications themselves do not reside at the application layer. It receives information directly from users and displays incoming data to the user. The Application Layer in the OSI model is the layer that is the “closest to the end user”. The layers, and what they represent, are as follows: Layer 7 - Application Most descriptions of the OSI model go from top to bottom, with the numbers going from Layer 7 down to Layer 1. Conceived in the 1970s when computer networking was taking off, two separate models were merged in 1983 and published in 1984 to create the OSI model that most people are familiar with today.
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