Before I take off more advanced CCNA topics, I feel like I should first re-visit the fundamentals. This will help any reader who is starting out, and it will ensure that I myself am building on a solid foundation. Every baseball player re-visits the fundamentals in spring training camp; by the same hand I know that I would also benefit from some fundamental.
The fundamental concept that builds networks today is the Open Systems Interconnect (OSI) model. This model drives the design of network appliances, network application software, network protocols, and network cabling. It also assists the field engineer with designing and troubleshooting networks. Understanding the OSI Model is essential if you wish to have success at any level or in any function of networking.
The OSI model describes the seven logical layers of networking. This is not something tangible; you cannot hold an OSI layer in your hand or click on an icon to view it. You can hold or click on items that are examples of the OSI concept, but in the end these are just concepts that all the networking geeks have agreed on.
The real purpose of the OSI model when it was first written was to make sure that everyone who designed a piece of hardware or software intended for a network could do so and ensure that it would be compatible with all the other devices in a network. The OSI model is like a framework upon which to build the details of network communications. The details are listed elsewhere, such as by the Internet Engineering Task Force and the Institute of Electrical and Electronic Engineers.
The OSI Model consists of seven layers:
- Physical
- Data Link
- Network
- Transport
- Session
- Presentation
- Application
In the future, I will describe each layer in a little more depth.
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