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OSI Model Layers

The knowledge of OSI model layers would help in understanding this widely used communication model. A short description of the 7 OSI layers is provided in the following article...
The abbreviation OSI stands for 'Open System Interconnection'. The OSI reference model is a network protocol design of communication divided in 7 layers. If we go from bottom to top, the 7 layers of this model are as follows: Physical Layer, Data Link, Network, Transport, Session, Presentation and Application. All the layers of OSI model are interdependent and provide services to upper and lower layers. These services are provided by 'instances'. The OSI model was developed in 1984 by the International Organization for Standardization (ISO). It is a standard communication networking model which can be used on networks having different applications and equipment.

OSI 7 Layer Model of Network Communication

The information about OSI model layers devices is interspersed in the paragraphs below.

Physical Layer
The physical and electrical specifications for the various devices used in the functioning of the communication network are defined in this layer. The layout of various devices which compose the network on a primary level is presented in the physical layer.

Data Link
The procedures needed for communication between entities of the network are defined in this layer. Errors which may occur in the physical layer are detected and corrected in this layer. The task of framing packets too is carried out in this layer.

Network Layer
In this layer, procedural and functional means for the transfer of variable length data sequences from the source to destination are provided. The process of data transfer takes place through different networks. The function of routing, fragmentation, reassembly and reporting delivery errors is carried out in this layer.

Transport Layer
The main task of the transport layer is to enable data transfer between end users in a transparent manner. The result/effect of maintaining transparency in the transfer of data is that upper layers of the OSI model are provided with reliable data transfer services.

Session Layer
The connections between computers are controlled by means of this layer. The session layer is needed for establishing, managing and terminating the connections between remote and local applications. Processes like checkpointing, termination and adjournment are also carried out by the session layer.

Presentation Layer
The core/main functionality of this layer is to present data in such a manner that, the application layer accepts it. The need to represent data in different formats doesn't arise. This is because the conversion of data from network format to application format and vice versa is done by the presentation layer.

Application Layer
The application layer is where end users interact with the communication system. This layer identifies communicating partners. It then checks for resource availability. Synchronizing the process of communication is one of the 3 tasks of the application layer.

History of OSI Model

The development of the OSI model started in the year 1970. The International Organization for Standards (ISO) started the development of architecture for this computer networking model. The concept of the ISO OSI Model evolved from the CYCLADES network. The CYCLDES network also had an influence on the inception and development of Internet technology.

The OSI model layer functions described in the paragraphs above provide us with basic knowledge about how the model works.
By Shashank Nakate
Last Updated: 9/23/2011
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