Thursday, November 21, 2013

Application Layer, Presentation Layer & Session Layer

What is Application Layer?
In OSI communications model, the application layer provides server for an application program to ensure that effective communication with another application program in a network isi possible.
The application layer is not the application but it is a service layer that provide service:
1. To Make sure the other party is identified and can be reached.
2. To make sure either the message sender or receiver or both.
3. To make sure that necessary communication resources exist
(for example, is there any modem in the sender’s computer?)
4. To makes sure aggrement at both ends about error recovery procedures, data integrity and privacy
5. To specify protocol and data syntax rules at the application level
The example protocol that working in application layer :
Protocol is a rule or standart that set or permit that connection, communication and data move is happen between 2 or more device.
In other word, application layer is interface between application with network functionality.
Presentation Layer
Presentation Layer have a function to data translation for data which want to transmitted from application in format that can been transmitted in network.
Presentation layer has responsibility how data can be converted and formated for data transfer.
the example of conversion data is format text ASCII for document, .gif and JPG for image.
This layer create code convert , data translation, encryption and
The example protocol in this level is RTF,MIDI,JPEG,etc.
RTF (Rich Text Format) is a file format that lets you exchange text files between different word processors, even in different operating systems.
Session Layer
Session Layer is responsible for setting up, managing, and then seperate session between Presentation layer entities.
This layer also provides dialogue control between devices, or nodes.
It coordinate communication between systems, and serves to organize their communication by offering three different modes: simplex,half duplex and full duplex.
The protocol that work in this layer is NFS,SQL,RPC,X Windows, ASP, etc.


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