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�SESSION, PRESENTATION & APPLICATION LAYER �OF �OSI MODEL �

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INTRODUCTION

  • OSI stands for Open System Interconnection is a reference model that describes how information from a software.

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  • OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications.

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  • OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.

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  • OSI consists of seven layers, and each layer performs a particular network function.
  • Each layer is self-contained, so that task assigned to each layer can be performed independently.

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CHARACTERISTICS OF OSI MODEL

  • THE OSI MODEL IS DIVIDED INTO TWO LAYERS: UPPER LAYERS AND LOWER LAYERS.

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LAYERS OF OSI MODEL

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  • The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software.
  • The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software.

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FUNCTIONS OF THE OSI LAYERS

  • There are the seven OSI layers. Each layer has different functions. A list of seven layers are given below:
  • Physical Layer
  • Data-Link Layer
  • Network Layer
  • Transport Layer
  • Session Layer
  • Presentation Layer
  • Application Layer

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SESSION LAYER

  • It is a layer 3 in the OSI model.
  • The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices.

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DIAGRAM OF SESSION LAYER

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FUNCTIONS OF SESSION LAYER

  • Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either half-duplex or full-duplex.

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  • Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery.

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PRESENTATION LAYER

  • A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems.

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DIAGRAM OF PRESENTATION

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  • It acts as a data translator for a network.
  • This layer is a part of the operating system that converts the data from one presentation format to another format.
  • The Presentation layer is also known as the syntax layer.

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FUNCTIONS OF PRESENTATION LAYER

  • Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end.

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  • Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network.

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  • Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video.

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APPLICATION LAYER

  • An application layer serves as a window for users and application processes to access network service.

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DIAGRAM OF APPLICATION LAYER

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  • It handles issues such as network transparency, resource allocation, etc.
  • An application layer is not an application, but it performs the application layer functions.
  • This layer provides the network services to the end-users.

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FUNCTIONS OF APPLICATION LAYER

  • File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer.

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  • Mail services: An application layer provides the facility for email forwarding and storage.
  • Directory services: An application provides the distributed database sources and is used to provide that global information about various objects.

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