Why Understanding The OSI Reference Model Is Important To You
A lot of networking books and other resources gloss over the OSI Reference Model, including only passing mention of it, or relegating it to an appendix. The usual stated reason for this is that the OSI model is too theoretical and doesn't apply to modern networking protocols like TCP/IP.
I believe that this is a misguided notion. While it is certainly true the OSI model is primarily theoretical, and that networking protocols aren't always designed to fit strictly within the confines of its layers, it's not true that the OSI model has little applicability to the real world. In fact, it is difficult to read about networking technology today without seeing references to the OSI model and its layers, because the models structure helps to frame discussions of protocols and contrast various technologies.
As just a few examples: the OSI Reference Model provides the basis for understanding how technologies like Ethernet and HomePNA have some important similarities; it explains how a PC can communicate using any of several different sets of protocols, even simultaneously; it is an important part of understanding the differences between interconnection devices such as repeaters, hubs, bridges, switches and routers; and it also explains how many WAN technologies interoperate.
Far from being obsolete, the OSI model layers are now showing up more than ever in discussions of technology. In fact, some protocols are even named specifically in terms of their place in the OSI Reference Model! For an example, consider the Layer Two Tunneling Protocol. Also, switches are now commonly categorized as being layer 2, layer 3 or even higher-layer switches.
In theoretical discussions, the OSI Reference Model helps you understand how networks and network protocols function. In the real world, it also helps you figure out which protocols and devices can interact with each other. So, I encourage you to read on. It's time well spent.
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