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OSI Reference Model

Last update:2/13/2012 1:53:00 PM

Owner and writer:Fatih KABAKCI

The purpose of this project is to introduce OSI(Open Systems Interconnection) reference model that is mentioned frequently in computer networks and other science and to encode in Java Applet platform.


OSI(Open Systems Interconnection) model is a concept that was improved about open systems architecture as the results of works that is carried by a sub-comitte created by ISO(International Organisation For Standarts) in 1977 and introduced by ITU-T confirmed X.200 series in 1984.
The concept of open systems are base on creating an integrated communications environment that end units can communicate each other according to accepted protocols hardware independed. OSI is only relates to the exchange of information between open systems but it is not related works of open systems on its own.

OSI model defines layered structure that need to comply some protocols due to can communicate between open systems.OSI seperated 7 layers each of communications operations of between open systems.Each of these layers provide service to the upper layer.


OSI model which contains intermediate system for a communication system is shown above.Intermediate system can be a switching or routing unit.The connection of between open systems is established on a physcial environment.
The following are required establishment of OSI reference model,
  • must create a layer when a group of different process is needed.
  • Each layer must satisfy a well-defined function.
  • Function of each layer must be defined considering standards of international protocol.
  • The limits of function of layer must be selected to minimize data flow between layers interfaces.
  • The number of layers must be excess until does not load different functions in the same layer,besides less until the layer will not cause a large number of architectural structure.

Data Communication in OSI

Data communication of OSI model is occured as a results of the layers in order to make the task.in case of sending data,this order is from top to bottom,in case of retrieval related order is from bottom to top. A case of sending data from the upper layers, each layer adding additional information, while a sub-layer, in the case of getting the rest of After the release of its own, using the additional information to transmit to the upper layer. Accordance with the OSI model, the two computers of the other B on A over the application message (data) is sent, if the protocol data units (PDU) generated by layers.if one of Two Computers are suitable for OSI send data the other one,protocol data units (PDU) is created by the layers.


The planning of this project was based on the above schema.
Any number of routers(at least 2, most 5) between the program which has two end system. The program starts with the first user interface screen is a window that asked the number of routers. The user has the right to enter at least 2 up to 5 routers. Then the correlation with the number entered in the router, you will be prompted to enter values for each metric between the router lines. Bandwidth of the user, after entering the values of the parallel simulation is configured as a metric. In the meantime, an information window is displayed. In this window, ’START’, ’OK’ and ’END’ function is called three pieces. The first stage, ’START’ on the left with the simulation starts and the computer screen to the right place a request to send data to the computer. Data, E-mail the sample data are given in the simulation, each element of the corresponding layer by layer, after being a per-header (header) information is sent by adding a sub-layer. In the meantime, the information window appears after each title in the process of adding information to the user has come. User, or ’END’ button again until the end of the program disable the display of the window. Information window, except for a short information messages shown in the middle of the screen. A tip of the frame system simulation, the user has specified by the metric values, using the shortest path routing table, the minimum tree makes browsing.
Simulasyondaki Uç sistem A’dan çıkan frame,kullanıcının belirtmiş olduğu metric değerlere göre,routing tablosunu kullanarak en kısa yol,asgari tarama ağacını(minimum spanning tree) çıkarır.At this point, which is one of the Dijkstra algorithm shortest path algorithm is used algorithms.

Dijkstra algorithm:

Dijkstra’s algorithm, according to a specific starting point is an algorithm that determines the shortest path.Dijkstra algorithm indicates the shortest path From starting node,A router is a starting node in the simulation,to other nodes.
Dijkstra algorithm was improved for weighted and directed graphs but this property is for edges that are greater than zero.This algorithm determines mininmum spanning tree by using Greedy approach.Thus,routers chooses the shortest path from A to end system B with calculating routing table by Dijkstra algorithm.
In conclusion the program that is described above was created target design in Java Applet technology.


You may access the application file here

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