Introduction the OSI Model

The OSI model was designed to promote interchangeability by treating a guideline for network data transmission between computers and components that have different hardware vendors, software, operating systems, and protocols. For example, look at the simple,process of transferring a file. Form a user’s perspective, a single operation has been performed to transfer the file. In reality, however, many different procedures had to take place behind the scenes to accomplish this seemingly simple task. Network data transmission (like the file transfer) is  performed through the use of a protocol suite, also known as a protocol stack, especially when installed in a given device.

A protocol is most easily defined as a set of rules used to determine how devices communication with each other. It is similar to language. If one person speaks English and another speaks English, they can communicate. But if one person speaks only spanish and the other speaks only English, they won’t be able to communicate. A protocol suite is a set of similar protocols that work together to make sure communicate happen properly.

The OSI model is used to describe what tasks a protocol suite performs as you explore how data moves from the user interface of a transmitter down to its physical network access, across a network, and then up the receiving device to its user interface. Keep in mind that not all protocols map directly to the guideline provided for us through the OSI model, but there are enough similarities so that you can use the OSI model to examine how these protocols function. This is one of the OSI model’s greatest advantages. It is at once very specific in the separation of functionality within a device (specifying more layers than most other models) and very generic in how it explains what happens at each layer. With this duality, networking engineers and administrators are able to make both broad comparisons and precise distinctions between the functionality and interchangeability of different protocol stacks. There are a myriad of protocol suites in use today, including IPX/SPX, NetBIOS, and TCP/IP, with the first two being quite a bit less prolific in today’s market than the last one. Each performs a specific function. Many of these functions that are provided through the use of protocol stack and its components are standard functions performed by other components in other protocol stacks, thus paving the way for devices and software that can enable the interoperation between differing stacks.

The most commonly referenced protocol model, the OSI model, was developed in 1977 by the International Organization for Standardization (commonly ref erred to as ISO) to provide “common gourd” when describing any network protocol.

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