El Haj Sleiman Batoul Hadi. Optimization models of fault-tolerant and secure routing in a telecommunication network over disjoint paths. – Qualifying scientific work on manuscript rights.
Dissertation for the Doctor of Philosophy (Ph.D.) degree in specialty 172 – Telecommunications and Radio Engineering. – Kharkiv National University of Radio Electronics, Kharkiv, 2023.
The dissertation solves an actual scientific and practical problem of optimizing the fault-tolerant and secure routing processes over disjoint paths in telecommunication networks (TCNs) by developing, improving, and investigating appropriate mathematical models.
The analysis results confirmed the importance and priority of Quality of Service (QoS), fault tolerance, and network security in modern and prospective telecommunication networks. It is emphasized that to achieve this goal, the functionality of advanced traffic management technologies, and especially routing protocols, should be used to the maximum extent possible. The latest routing protocols should support multipath solutions, calculate paths that provide high indicators of Quality of Service and network security, and implement schemes of local, segment, and global protection (redundancy) of bandwidth and network elements under conditions of single and multiple failures.
The problems of improving mathematical models, methods, and protocols of routing in TCN with their adaptation to modern requirements come to the forefront. An effective direction of routing models and methods improvement is the use of disjoint paths, which allows the introduction and further effective and optimal use of the network resources redundancy for systemic increase of QoS level, fault tolerance, and network security.
The mathematical models of QoS routing in a telecommunication network over disjoint paths are improved in the dissertation work. The scientific novelty of the first mathematical model consists of introducing new conditions for balancing the routes’ capacity and using an updated optimality criterion of routing solutions, which allowed to ensure the maximization of the number and total capacity of the calculated paths in the routing process. The analysis of the study results showed that using the proposed model makes it possible to ensure the maximum possible bandwidth of the routing solution represented by a set of disjoint paths in cases of high network heterogeneity, i.e., when the bandwidths of TCN links differ significantly.
The scientific novelty of the second mathematical model consists of introducing new bilinear conditions to ensure guaranteed total routes’ capacity, which allows calculating paths with a bandwidth not lower than the established threshold (requirement). Depending on the form of the chosen optimality criterion, these conditions can be met either by increasing the number of disjoint routes involved or by raising the threshold for their minimum bandwidth. Improved models increased the total bandwidth of the calculated disjoint paths in TCN from 1.5-10% to 18.6-42%.
Mathematical models of secure QoS routing over disjoint paths have been further developed in this work. The proposed models' novelty lies in using a complex optimality criterion of routing solutions, which, along with bandwidth indicators, considers the network security parameters of communication links – the probability of their compromise. This made it possible to calculate such a set of paths in TCN, which, firstly, did not intersect; secondly, their number was the maximum possible; thirdly, their total bandwidth was either the maximum possible or not lower than the specified one; fourthly, the compromise probability of these paths was minimal. Computational examples demonstrate the functionality of the proposed mathematical models, their efficiency and adequacy, as well as their effectiveness in terms of implementing secure routing in TCN. It is established that the provision of guarantees for the multipath bandwidth occurs, as a rule, with a certain, and sometimes significant, margin since the linear conditions for ensuring the guaranteed QoS are formulated for the worst case when all routes calculated and included in the optimal multipath have approximately the same bandwidth.
The research results have shown that the application of the proposed models of secure routing in TCN allows for a decrease in the multipath compromise probability from 13 to 19% depending on the level of network security of communication links and reduce the compromise probability of confidential messages on average from 23-27 to 47-55% for different cases of compromise probability of links and routes of the network. Applying the proposed model of secure routing with Quality of Service guarantees in terms of bandwidth has improved the probability of multipath compromise from 9-11.5% to 19.5-47% on average for different cases of values of links compromise probabilities.
