When the networks first came into being, computers could typically comunicate only with computers from the same manufacture. Now take a look at the sample below ;)
The Companies ran either a complete DECnet solution for an IBM solution but not together
So, In the late 1970s(CMIIW), the OSI(Open Systems Interconnection) Model was created by the International Organization for Standardization interoperable network devices. It’s look like a world peace right? :)) It will probably never happen completely, but I think it’s still a great goal :P
The OSI Model is the primary architectural model for networks. It describes how data and network information are communicated from application on the computer, through the network media, to an application on another computer. The OSI reference model breaks this approach into layers.
So, what the hell is reference model? It’s look like a conceptual blueprint of how communications should take place. It addresses all the processes requied for effective communication and divides these processes into logical groupings called layers. When a communication system is designed in this manner, it’s known as layered architecture.
Confused? Great :)) Now, Check this story out and you’ll understand ;)
You and some friends want to start a company. One of the first things you’d do is sit down and think through what must be done, who will do them, what order they will be done in, and how they relate to each other. Ultimately, you might group these tasks into departments. Let’s say you decide to have an order-taking department, an inventory department, and a shipping department. Each of your department has its own unique task, keeping its staff members busy and requiring them to focus on only their own duties.
So, In this scenario, departments are metaphor for the layers in a communication system. For things to run smoothly, the staff of each department will have to both trust and rely heavily on the others to do their jobs and competently handle their unique responsibilities. In your planning sessions, you would probably take notes, recording the entire process to facilitate later discussions about SOP(Standards of Operation) that will serve as your business blueprint, or reference model.
Once your business is launched, your department heads, armed with the part of the blueprint relating to their department, will need to develop practical methods to implement their assigned tasks. These practical methods, or protocols, will need to be compiled into a standard operating procedures manual and followed closely. Each of the various procedures in your manual will have been included for different reasons and have varying degrees of importance and implementation. If you form a partnership or acquire another company, it will be imperative for its business protocols.
Similarly, software developers can use a reference model to understand computer communication processes and to see what types of function need to be accomplished on any one layer. If they’re developing a protocol for a certain layer, all the need to concern themselves with is the specific layer’s functions, not those of any other layer. Another layer and protocol will handle the other functions. The technical term for this idea is binding. The communication processes that are related to each other are bound, or grouped together as particular layer.
Reference: Lammle, Todd (2007). CCNA Study Guide. Washington DC: Willey Publishing