The 7 Layers of the OSI Model and their Purpose

February 5, 2021

The 7 layers of the OSI model
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The Open Systems Interconnection (OSI) is the standard for the implementation of protocols in the layers. It comprises seven (7) layers. In this post, we will discuss the role each layer plays in the model.

Application layer (Layer 7)

This is the layer that the user interacts with by using various application software. It handles both file transfer and access. It receives data from and provides data to the Presentation layer.

Presentation layer (Layer 6)

It takes care of the syntax of information transmitted. It sees to it that the data transmitted is presented in a way that can be understood by different computers with different data representation. This makes it possible for different computers to understand each other.

Session layer (Layer 5)

It opens sessions, form of communications between users. It controls the flow of data. It establishes the rules of the communication. For example, how machines should communicate in turn, simultaneous communication and synchronization.

Transport layer (Layer 4)

As its name indicates, the transport layer transports data across the network. It receives data and breaks it into smaller transmissible frames that are forwarded to the network layer. It ensures a successful transmission of data from the source to the destination.

Network layer (Layer 3)

This layer performs routing operations whereby frames containing source and destination addresses from the datalink layer are examined to check successful delivery of each frame. The network layer also manages traffic load.

Datalink layer (Layer 2)

It obtains data from layer 1 (Physical layer), checks the data and transforms it into frames that are error free before forwarding them to the network layer. An acknowledgement frame is then sent by the receiver to assure the sender for a successful reception of the frames when the communication is secure. The data link layer is divided into two sublayers: The Media Access Control (MAC) which is responsible for managing access to the physical network medium and the Logical Link Control (LLC) responsible for managing flow control, notification and error-checking functions of the datalink layer

Physical layer (Layer 1)

The physical layer is responsible of the physical aspects of the network comprising fibefr optic cables, cards, hubs, repeaters etc. The physical layer specifies what the physical aspects of the network are, what tasks they must be able to perform and how they should perform those given tasks. The physical layer is responsible for transmitting bits using signalling type over communication channels.


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