OSI Reference Model

 

The OSI Model consists of the following seven layers: Application Presentation Session Transport Network Data Link Physical

What do the 7 layers really do?
 

When data is being transferred and shared over a network, it must pass through each of the 7 layers in one machine, from the application layer down, before zipping across a network and working its way up the layers in the receiving machine.

The OSI Model
 

The main use of the model is to help network designers understand the functionality involved with the development and flow of data communications. Included within this model are the protocols for network properties and transmission methods. The model is divided into 7 layers, with individual characteristics and tasks within each layer. Each layer must communicate with the layer directly above and below through a series of standards and protocols.

Illustration with Images Text Application Layer: Provides network services to user applications. It is responsible for exchanging information between programs running on the machine, such as an e-mail program, and other services running on a network, such as a print server or another computers' application. Presentation Layer: Concerned with how data is converted and formatted for data transfer. Examples of format conversions include ASCII text for documents and .gif and JPG for images. This layer performs code conversion, data translation, compression and encryption. Session Layer: Determines how two devices establish, maintain and manage a connection - how they talk to each other. These connections are called sessions. Transport Layer: Responsible for breaking the data into segments, establishing an end-to-end logical connection between machines, and providing for error handling. Network Layer:  Responsible for determining addressing on the network, determining the routes that information will take on its journey, and managing network traffic congestion. Data at this level is packaged into packets. Data Link Layer: Provides the link for how data, packaged into frames is communicated through hardware to be transported across a medium. It communicates with network cards, manages physical layer communications between connecting systems and handles error notification. Physical Layer: Specifies how data is processed into bits and physically transferred over medium, such as cables. It's responsible for activating and maintaining the physical link between systems.

Posted in: