Networking - Osi Model

Introduction:

The concept of networking is so essential in this fast-moving world now a days, for the purpose of sharing information and resources. Open Systems Interconnection (OSI) reference model proposed by the International Standards Organization (ISO) has been so successful to create an intellectual framework within which to clarify network concepts and activities. Today, OSI reference model has become a key part of networking. The IEEE 802 is an enhancement to the OSI model. With OSI model, networking can be broken into seven layers. Therefore, the complexity of networked communications, from application to hardware is broken into a series of interconnected tasks and activities. It creates a method to solve big problem by deconstructing them into a series of smaller problems that can then be solved individually.

OSI History

The OSI (open Systems interconnection) model was developed by the International Standards Organization (ISO) in 1984 in an attempt to provide some standard to the way networking should work. It is a theoretical layered model in which the notion of networking is divided into several layers, each of which defines specific functions and features. However it must be noted that this model only represents a general guideline for developing usable network interfaces and protocols. Sometimes it may become very difficult to distinguish between each layer as some systems do not rigorously adhere to the model. Despite all this, however the OSI model has earned the honour of being "the model" upon which all good network protocols are based.

Principles used in defining OSI layers

The basic idea behind the design of the OSI model was to create enough layers to make each layer manageably small, but it should not have so many layers that the processing overhead imposed by the collection of layers is burdensome.

The important principles are:

* Do NOT create so many layers that the task of describing and integrating the layers is more difficult than necessary.

* Create a boundary at a point where the number of interactions across the boundary are minimized and use past experience to ensure high probability of success.

* Create separate layers to handle functions that are different in the process performed or the technology involved.

* Collect similar functions into the same layer.

* Allow bypassing of sub layers.

* Allow changes of functions and protocols to be made within a layer with affecting other layers.

* Create a layer of easily localized functions so that the layer can be totally redesigned to make