OSI Reference Model

OSI Reference Model


The OSI reference model is a general-purpose framework define the characteristics and standards of how computers communicate with one another. It is a conceptual model and not a physical model.




The OSI model consists of 7 layers in which each layer consists of a certain set of functions that enable efficient, secure and reliable transmission of data

The layers of the OSI model are as follows:

Application layer (layer 7):

he main purpose of this layer is to provide network services to the applications of the users. Beyond that, it establishes the availability of the intended communication partners, as well as synchronizes and establishes agreement on procedures for error recovery and data control integrity.

Being the final layer of the OS model, it differs from the other layers such that it does not provide service to the layers above it.

Presentation Layer (Layer 6):

The purpose of this layer ensures that information sent by layer 7 from one system to another is readable by both computers involved. It can translate among multiple data formats using a common encoding.

Session Layer (Layer 5):

The function of this layer, as the name implies, related to everything about sessions.

A session is basically the time a user spends on a particular computer, network or software. It starts when the users log in and ends when the user logs out.

This layer establishes and terminates the session, as well as synchronizes dialogue between the presentation layers of the 2 hosts. It is also responsible for efficient data transfer, class of service and exception reporting of the upper layers.

Transport Layer (Layer 4):

The service this layer provides to the layers above it, I.e the application layers, is error recovery. This is accomplished with the help of acknowledgements.

When data is segmented in the transport layer before being sent, a sequence number is added to the transport layer header. When data is sent to the recipient, the sequence number of the segment is shown in the header.

In case a segment is not received during transmission of the data, the recipient, on viewing the sequence number will send a TCP segment, alerting the sender to send the lost segment again.

Network Layer (Layer 3):

The function of this layer to find a path through which data can be sent from source to destination. The main protocol concerned with this layer is the Internet Protocol.

The internet Protocol (IP) which is responsible for transfer of data does this by providing connectivity to the computers within the computer network via logical addressing

Datalink Layer (Layer 2):

This layer defines the type of format suitable for transmission via the physical layer. It includes the data formats necessary, as well as access control, of the physical layer

More than that, it also includes an error detection and correction system to ensure reliable delivery of data.

Physical Layer (Layer 1):

This layer is concerned with the physical aspects of the computer network. It includes everything from the cabling, connector types, types of cabling, voltage, etc. Essentially it concerns with everything related to the physical aspect of a computer network

OSI Reference Model OSI Reference Model Reviewed by Sirf Tech on February 22, 2022 Rating: 5

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