Computer Networks and distributed Systems

as part of the BMBF-Compound Project SIMBA — „Key Concepts of Informatics in multi medial Elements under special Consideration of Women's specific Learning Interests”

Advice for Teachers - Peer-To-Peer Networks

In Peer-to-Peer-Systems organized centrally single computers are connected to a central server, which, in its data-base, has entries for all of the computers connected to it as well as the available data files. The server's function is merely to give information about the resources available. After receiving the requested information further communication may take place directly between peers.

In local Peer-to-Peer-Systems no central server is needed. Here, every computer involved may send and receive inquiries, thus, according to this model, both being client and server. An inquiry, therefore, may spread until it is received by every computer throughout the network. If a computer has the file searched for available, it notifies the inquiring peer. Then a direct connection between both of these computers may be established and the data transfer may take place.

The applet introduced below simulates a music share software. It is possible to simulate both a central and a local Peer-to-Peer-System. The functionality is limited to the essential features of such an application: Search, data transfer, and listing of the files existing locally on ones own computer. On the left side of the menu the choice between a central and a local network may be made. This possibility of adjusting this application usually does not exist in practise.

Although it has some potential of interactivity, primarily it is thought to visualize the operating mode as part of an introduction to the field of Peer-to-Peer-Networks.

After choosing a system any title may be searched for. If these are available within the network, a virtual file transfer may take place.

Illustration 1: Starting Template of the Peer-to-Peer Application

If a key word is entered in the menu "Search", then the single steps of the search- as well as of the following transfer process are displayed successively according to the respective system. In this context each step meets with a logical unit and, by the means of the ">>" button, the user moves one step forward at a time.

Illustration 2: Search in the central system

Illustration 3: Search in the decentral system

After a successful download the files are displayed in the local MyMusic-List.

Illustration 4: MyMusic List of the transferred music files in the central system

Illustration 5: MyMusic List of the transferred music files in the decentral system

Click here to get to the material

Please note that it is illegal in some countries to use file sharing tools to download music, movies, etc. .