OSI model

                              OSI  MODEL


Introduction to OSI Model




~ OSI model is based o the proposal developed by
the international standards organizatin(ISO).

 ~ This model is called ISO OSI (Open Systems Interconnection) Reference model because it deals with connecting open systems (systems that are open for communication with other systems).

 ~ We call it as OSI Model.




 Physical layer :
                                               
                           *  Provides physical interface for transmisssion of information.

 * Define rules by which bits are passed from one system to another on a physical communication medium.
Data link layer :


                                      * data linl layer attempts to provide reliaable communication over the phycial layer interface.
 * Breaks the out going data into frames the reassemble the recived frames.
Network layer :

           
                                     * Implements routing of frames (packets) through the networks.
* Define the most optimum path the packet should take from the source to the destination.
* Defines logical addressitng so that any end point can be identified.

 Transport layer :


                                           * Propose of this layer is to provide a reliable mechanism for the exchange of data between two processes in diffrent computer.
* Ensure that the data units are delivered error free.
* Ensure that data units are delivered in sequence.
* Ensure that there is no loss or duplication of data units.

 Screen layer :

                       * Session layer provides mechanism for controlling the dialogue between the two end system. it defines how to start, control and end conversations (called session) between applications.
* This layer request for the logical connection to be established on an end user's request.

 Presentation layer :

                                                      * Presentation layer defines the format in which the is to be exchanged between the two communicating entities.
*Also handels data compression and data encryption (cryptography).
Application layer :

                                                   * Application layer intracts with Application programs ans is the higest level of ISO model.
* Application layer contains menagement function to support distributed applications.
* Example of application layer are applications such as file transfer.
electronic mail, remote login etc...
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