OSI MODEL: Open System Interconnection

Hello friends, In this blog post I am going to let you know about a very popular communication model that is OSI model. It is also known as an open system interconnection model(OSI).

OSI model is a layered framework for the design of a network system which permits communication across all kinds of computer systems. It has seven separate but related layers, each of which defines a segment of the process of moving information across a network.

Now, for better understanding, the fundamental of the OSI model see the below-given head categorization.

(OSI Model)Layered Architecture:

The OSI model is made of seven ordered layers which are also known as the physical layer, Data link layer, network layer, transport layer, session layer, presentation layer, and application layer. Fig 1 shows the architecture of the OSI model.

Fig.1 OSI Model – Layer Architecture

When the message travels from one device to another, it may pass through several intermediate nodes. Usually, these intermediate nodes involve only the first three layers of the OSI model. In developing the model, the designers distilled the process of transmitting the data down to its most fundamental elements.

They identified the network functions that had related uses and collected those functions into discrete groups which became the layers. Each layer defines a family of functions that are distinct from those of the other layers.

By defining and localizing the functionality in this way, the designers developed an architecture that is both comprehensive and flexible. The most important thing is that the OSI model permits complete transparency between otherwise incompatible systems.

Peer to Peer Process:

Every layer in the OSI model calls upon the services of the layer just below it within a single machine. For example, layer 3 uses the service given by layer 2 and gives service to layer 4. Between machines, layer x on the machine communicates with layer x on another machine.

This communication is governed by an agreed-upon series of rules and conventions known as protocols. A process on each machine that communicates at a given layer are known as peer to peer processes. Therefore, communication between machines is peer to peer process using the protocols suitable to a given layer.

The interface between layers:

In the OSI model, the interfaces between each pair of adjacent layers make possible the passing of the data and network information down through the layers of the sending machine. Every interface defines what information and services a layer must provide for the layer above it.

As long as a layer still gives the expected services to the layer above it, the specific implementation of its functions can be modified or replaced without needing changes to the surrounding layers.

Organization of the layers:

In the OSI model, the seven layers can be divided into three subgroups. The physical layer, data link layer, the network layer is the network support layers. The physical aspects of moving data from one device to another device(such as electrical specification, physical connections, physical addressing and transport timing, and reliability) are dealt with by these devices.

The session layer, presentation layer, and application layer are the user support layers. They permit interoperability among unrelated software systems. The transport layer ensures an end to end reliable data transmission while the data link layer ensures reliable transmission on a single link.

The upper OSI layers are almost always implemented in software and lower layers are a combination of hardware and software, except for the physical layer, which is mostly hardware.

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