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 - Routing

The topic of this chapter is the problem, how a packet coming from a transmitter arrives at a receiver. In this context the center of attention is the network layer, which calculates the paths by the means of routing algorithms. In the case of virtual leads, route calculation needs to be done only one time since all packets take the same path. In Datagram-Networks, including IP-Networks, routing is relevant to every packet as the packets may take different paths. In both cases a router needs the packet's address of destination in order to look up a suitable source port in its routing map. This procedure is called forwarding. Routing is the process, in the course of which routing maps are provided. It is important to distinguish between these two terms. In the following Flash-Animation the two predominating classes of Routing-Algorithms are treated: Link-State-Routing and Distance-Vector-Routing.

Each of the algorithms is illustrated by the means of an animation, which shows how the algorithms work, presenting the process graphically step by step (see illustrations 1 and 2).

Illustration 1: Visualization flow regarding Distance-Vector-Routing

Illustration 2: Visualization flow regarding Link-State-Routing

Within the animation the user may skip single steps forwards as well as backwards. Thus it may be adjusted to any user's individual pace of learning. Moreover, this option allows to consider a single step selectively, in case the materials are not to be treated exhaustively.

Besides of the animations every topic provides an exercise mode as well. In the case of the Distance-Vector-Algorithm the routing maps are given by two routers. Based on the maps the student is to develop the topology of the network. The connecting lines are provided by point-and-click onto a router and, while having the mouse button still clicked, drawing it to another router.

Illustration 3: Exercise regarding Distance-Vector-Routing

Once a network topology is created it may be checked upon by clicking the “Evaluate-Button“. The student is told, whether the topology is correct or not. Through clicking the button “Wrong Solutions“ all the connections, which are not correct, are deleted. With “Back“ the respective last connection is deleted, while “Reset“ deletes everything, offering the possibility to start all over.

Every network-user knows the use and the advantages of the method of routing. The simulations and visualizations of two important procedures offer the possibilities, which otherwise could only be accomplished through the assembly of networks for experimental purpose, which is an expensive as well as time-consuming affair. This object's practise element offers the right possibilities to work productively with the methods during learning phases as well as to draw up packet routes and have them checked by the means of maps.

In the visualization flows the explanation of the calculusses is connected to a schematic visualization. Here, in addition to the formal description, each of the single steps of the algorithm may be viewed simplified in a graphic form in schematic networks. Especially students at first have a hard time memorizing or understanding algorithms, which are some more complex. If visualizations or similar means are used systematically in respective places, students may be supported in solving common problems.

Besides of both of the Routing-Algorithms the student is able to gain an overview over the arrangement and tasks of the internet protocoll layers. The scenario is structured the way that the user is to navigate the character through the layer model. It consists of five corridors, each representing a layer. On every corridor there is a “secretary“ at a desk. If the secretary is approached from the front, the user receives the information necessary for the respective layer through a textbox. This box disappears again on confirming with “OK“. At the same time the door to the next layer opens and the user may visit the next "secretary". If the backpack of the character is clicked onto, the documents collected may be looked at once more. By clicking on one of the bag's buttons, the backpack is removed again. The character itself is navigated by the arrow keys of the keyboard.

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