Στο πλαίσιο της παρούσας διπλωματικής, παρατίθενται τα βασικά στοιχεία που συνθέτουν τους μηχανισμούς φήμης και πίστωσης ενώ περιγράφονται ορισμένοι που έχουν ήδη αναπτυχθεί από τη διεθνή βιβλιογραφία. Εν συνεχεία, αναπτύσσονται τα πλεονεκτήματα που προσφέρουν οι υβριδικοί μηχανισμοί κινήτρων (hybrid mechanisms), οι οποίοι αποτελούν συνδυασμό των άνωθεν μηχανισμών. Στο τέταρτο κεφάλαιο παρουσιάζεται αναλυτικά ο υβριδικός μηχανισμός ICARUS 2, που αποτελεί μία προέκταση του ήδη υπάρχοντος πρωτοκόλλου ICARUS που είχε αναπτυχθεί από την ερευνητική ομάδα του ΕΜΠ. Τέλος, παρατίθενται μία σειρά από προσομοιώσεις που εκτελέστηκαν με τη χρήση του ICARUS 2 καθώς και τα αντίστοιχα αποτελέσματα με σκοπό τη μελέτη της αποτελεσματικότητάς του. Εξάγονται ενδιαφέροντα συμπεράσματα.
(EL)
Upon the growth of fourth and new generation networks, the concept of wireless ad-hoc networks has started to implemented. This type of network is decentralized and is not characterized by a
central authority that inspects it and neither is based on an existing constant (either wired or wireless) infrastructure. On the contrary, it consists of simple and equivalent nodes, which act either as terminal nodes or as router nodes according to the network state. The entrance of nodes into the ad-hoc networks is not filtered by an inspector and results to a network grid that is shaped and hat can grow rapidly. In ad-hoc networks, the intentions of nodes do not always contribute to the improvement of the overall network performance, as they may show selfish or malicious behavior which downgrade the quality of service that the network serves.
For their compliance, it would be necessary to develop incentive mechanisms that encourage nodes to cooperate and punish the individualism strictly. Incentive mechanisms are divided into two great categories:reputation-based mechanisms and credit-based mechanisms. In the context of the current diploma thesis, the basic entities of the reputation and credit-based mechanisms are indicated and some examples are cited, that have already been developed and applied. Subsequently, an introduction to hybrid mechanisms is made, which are a combination of the reputation and credit based mechanisms, and their advantages are explained.
In chapter four, the hybrid mechanism ICARUS 2, an updated extension of the existing ICARUS protocol that has been developed in the context of the thesis, is analytically cited. Finally, some simulations to measure the algorithm efficiency in a network, that makes use of ICARUS 2 protocol, are executed and their results are presented.
(EN)
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