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Presentation Layer

 Presentation Layer

The presentation layer ensures interoperability among communicating devices.

It provides the necessary translation of data needed for transmission and at receiver changing that format into the one that is     understood  by the receiver.
 
It provides encryption and decryption for security purpose.
 
It provides compression and decompression to make transmission more efficient.
 
In particular , presentation layer is concerned with the syntax and semantics of the information transmitted.    

                   

Session Layer

Session Layer the 5th Layer in the 7 Layer OSI Reference Model

  •       Session layer (5th Layer) responds to service requests from the presentation layer ( 6th Layer ).

  •      Session layer (5th Layer) issues service requests to the transport layer ( 4th Layer )

  •    Session layer (5th Layer) is the thinnest Layer in the OSI Reference Model

 

Session Layer is the 5th Layer in the 7 Layer  Open Systems Interconnection (OSI)    reference model.Session layer (5th Layer) is the thinnest Layer in the OSI Reference Model.Session Layer take care of the dialogue between computers in network. The Session Layer Establishes, manages and terminates  sessions (dialogue between computers) in a communication network. When there occure a connction loss during a session the protocols in the session layer tries to recover the connection Or if a connection is not in use for a very long duration the protocols in the session layer may close the connection and may re-open it.

Functions of Session Layer

The session layer is the network dialogue controller. It establishes maintains and synchronizes the interaction between communicating devices. For example  It might manage an audio stream and video stream that are being combined in a teleconferencing application. 

Specific responsibilities of session layer includes :

          1) Session management.
          2) Synchronization.
          3) Dialogue control.
          4) Graceful close of the sessions.
          5) Token management.

If an application is working in half duplex mode only one side can transmit message at a time, both cannot send data simultaneously. Dialogue management can be implemented through the use of tockens.The user holding the tocken can only transmit the data.If a session get disconnected during   data transfer between two machines ,Then it is the responsibilty of the session layer to re-establish the connection and it helps to resume the data transfer from where it breaks. The session layer maintains check points  and these check points helps to resume the the data transfer or transaction process  from these points if any error occur during the process .