11 research outputs found
Ευφυής κατανομή πόρων σε δίκτυα επικοινωνιών
No full textThe use of information derived through networking plays a transformative role in many areas of human activity, including work, education, entertainment, and environmental monitoring. The need for networking for both people and any device that can produce useful information is growing, thus launching the volume of data that network infrastructures have to manage. In addition to the increased volume, networks must meet the evolving requirements that exist in the flow of information related to throughput, latency, reliability, and security.Faced with the aforementioned challenges, the operation of the networks is forced to follow its own evolution which is based on three main factors of different importance that interact with each other. The first and most important of these factors is the evolution of physical layer technologies, such as the transition from copper wire to fiber optics, the application of advanced modulation techniques and the improvement of the performance of the hardware used. The evolution of technology at the physical layer multiplies the available resources, enabling networks to improve both quantitatively and qualitatively the services they can provide. The second factor of networks development is the design and planning of their infrastructure, which is driven both by the new capabilities that come from the evolution of technologies of the physical level, and by the increased requirements of modern applications, thus creating new types of networks and technologies capable of coping with them. Such new technologies include software defined network, network function virtualization, big data networking and network slicing, while new types of networks include sensor networks, elastic optical networks, passive optical networks, and radioover fiber networks. The third factor is the creation of mechanisms that will control the effective operation of new network technologies. These mechanisms include the creation and development of protocols and algorithms whose purpose is the efficient use and distribution of available network resources. The evolution of network technologies, in addition to offering new capabilities and increased available resources, create problems of a high degree of complexity regarding their optimal utilization. For this reason, these mechanisms have to use advanced problem-solving methods and tools such as artificial intelligence and machine learning.The dissertation is related to the third factor of networks development and aims to explore and present solutions to open research issues, related to the creation of control and resources management mechanisms, concerning state of the art access and backbone networks. The PhD thesis consists of four parts in which protocols and algorithms which enhance the operation of radio over fiber, passive optical, elastic optical and sensor networks are proposed respectively. In all cases the efficiency of the proposed mechanisms is compared with relevant one from the literature using analytic simulation scenarios and results.Η χρήση της πληροφορίας μέσω των σύγχρονων δικτύων δεδομένων παίζει εξελικτικό ρόλο σε πολλούς τομείς της ανθρώπινης δραστηριότητας, συμπεριλαμβανομένης της εργασίας, της εκπαίδευσης, της ψυχαγωγίας και της παρακολούθησης του περιβάλλοντος. Η ανάγκη για δικτύωση τόσο για τους ανθρώπους όσο και για κάθε συσκευή που μπορεί να παράγει χρήσιμες πληροφορίες αυξάνεται, εκτοξεύοντας έτσι τον όγκο δεδομένων που πρέπει να διαχειριστούν οι δικτυακές υποδομές. Εκτός από τον αυξημένο όγκο, τα δίκτυα πρέπει να εξυπηρετούν τις εξελισσόμενες απαιτήσεις που υπάρχουν στη ροή πληροφοριών που σχετίζονται με την απόδοση, την καθυστέρηση, την αξιοπιστία και την ασφάλεια.Αντιμέτωπη με τις προαναφερθείσες προκλήσεις, η λειτουργία των δικτύων αναγκάζεται να ακολουθήσει τη δική της εξέλιξη που βασίζεται σε τρεις βασικούς παράγοντες διαφορετικής σημασίας που αλληλοεπιδρούν μεταξύ τους. Ο πρώτος και σημαντικότερος από αυτούς τους παράγοντες είναι η εξέλιξη των τεχνολογιών του φυσικού επιπέδου, όπως η μετάβαση από το σύρμα χαλκού στην οπτική ίνα, η εφαρμογή προηγμένων τεχνικών διαμόρφωσης και η βελτίωση της απόδοσης του υλικού που χρησιμοποιείται. Η εξέλιξη της τεχνολογίας στο φυσικό επίπεδο πολλαπλασιάζει τους διαθέσιμους πόρους, επιτρέποντας στα δίκτυα να βελτιώσουν τόσο ποσοτικά όσο και ποιοτικά τις υπηρεσίες που μπορούν να παρέχουν. Ο δεύτερος παράγοντας ανάπτυξης των δικτύων είναι ο σχεδιασμός και εξέλιξη των υποδομών τους, ο οποίος καθοδηγείται τόσο από τις νέες δυνατότητες που προέρχονται από την εξέλιξη των τεχνολογιών του φυσικού επιπέδου, όσο και από τις αυξημένες απαιτήσεις των σύγχρονων εφαρμογών, δημιουργώντας έτσι νέους τύπους δικτύων και τεχνολογιών ικανών να τις αντιμετωπίσουν. Τέτοιες νέες τεχνολογίες περιλαμβάνουν το διαδίκτυο των πραγμάτων, το δίκτυο καθορισμένο από λογισμικό (Software defined network), την εικονικοποίηση λειτουργιών δικτύου, τη δικτύωση μεγάλων δεδομένων , ενώ νέοι τύποι δικτύων περιλαμβάνουν δίκτυα αισθητήρων, ελαστικά οπτικά δίκτυα, παθητικά οπτικά δίκτυα και ασύρματα μέσω οπτικών ινών δίκτυα. Ο τρίτος παράγοντας είναι η δημιουργία μηχανισμών που θα ελέγχουν την αποτελεσματική λειτουργία των νέων τεχνολογιών δικτύου. Αυτοί οι μηχανισμοί περιλαμβάνουν τη δημιουργία και ανάπτυξη πρωτοκόλλων και αλγορίθμων που σκοπό έχουν την αποτελεσματική χρήση και διανομή των διαθέσιμων πόρων του δικτύου. Η εξέλιξη των τεχνολογιών δικτύου, εκτός από την προσφορά νέων δυνατοτήτων και αυξημένων διαθέσιμων πόρων, δημιουργεί προβλήματα υψηλού βαθμού πολυπλοκότητας όσον αφορά τη βέλτιστη αξιοποίησή τους. Για το λόγο αυτό, αυτοί οι μηχανισμοί πρέπει να χρησιμοποιούν προηγμένες μεθόδους και εργαλεία επίλυσης προβλημάτων όπως η τεχνητή νοημοσύνη και η μηχανική μάθηση.Η διατριβή σχετίζεται με τον τρίτο παράγοντα ανάπτυξης δικτύων και στοχεύει στη διερεύνηση και παρουσίαση λύσεων σε ανοιχτά ερευνητικά ζητήματα, που σχετίζονται με τη δημιουργία μηχανισμών ελέγχου και διαχείρισης πόρων, που αφορούν σύγχρονα δίκτυα πρόσβασης και κορμού. Η διδακτορική διατριβή αποτελείται από τέσσερα μέρη στα οποία προτείνονται πρωτόκολλα και αλγόριθμοι που βελτιώνουν τη λειτουργία των ασυρμάτων μέσω οπτικής ίνας, παθητικών οπτικών, ελαστικών οπτικών και δικτύων αισθητήρων αντίστοιχα. Σε όλες τις περιπτώσεις η αποτελεσματικότητα των προτεινόμενων μηχανισμών συγκρίνεται με αντίστοιχους από τη βιβλιογραφία χρησιμοποιώντας αναλυτικά σενάρια και αποτελέσματα προσομοίωσης
An Adaptive LoRaWAN MAC Protocol for Event Detection Applications
No full textIn recent years, the Internet of Things (IoT) is growing rapidly and gaining ground in a variety of fields. Such fields are environmental disasters, such as forest fires, that are becoming more common because of the environmental crisis and there is a need to properly manage them. Therefore, utilizing IoT for event detection and monitoring is an effective solution. A technique for monitoring such events over a large area is proposed in this research. This work makes use of the Long-Range Wide Area Network (LoRaWAN) protocol, which is capable to connect low-power devices distributed on large geographical areas. A learning-automata-based hybrid MAC model is suggested to reduce the transmission delay, when a small part of the network produces event packets stemming from an event occurrence that is related to environmental monitoring applications, such as events related to forest fires. The proposed hybrid MAC is evaluated via simulation, which indicates that it achieves significantly higher performance in terms of packet delay, when compared to traditional LoRaWAN schemes
Earthquake-Tolerant Energy-Aware Algorithm for WDM Backbone Network
No full textTraffic on backbone communication networks is growing significantly every year. This results in an increase in both energy consumption and the carbon footprint they leave on the environment. As a response, research efforts are focused on reducing energy consumption in telecom networks. Wavelength division multiplexing (WDM) optical networks are key for addressing rising bandwidth demands in backbone networks, but this leads to a concurrent surge in energy usage. Additionally, regions with high seismic activity risk damage to backbone networks from earthquakes, causing significant bandwidth loss and service disruptions. This paper aims to reduce the energy consumption in a backbone network by implementing an algorithm that optimizes energy efficiency while preserving network connectivity and resistance to earthquake phenomena. The proposed algorithm redesigns and modifies a backbone network by deactivating the unnecessary links without affecting the network performance. The scheme is extensively evaluated through simulations using real seismic data from the Geodynamic Institute of the National Observatory of Athens, confirming earthquake resilience and energy efficiency goals, with an energy saving of up to 9% compared to existing solutions
A TDMA-Based Access Protocol for Dense Networks with Moving Nodes for IoT Applications
No full textLow-power wide-area (LPWA) technologies have gained popularity in accordance with the explosive growth of the Internet of Things (IoT). Among others, LoRa is considered as the leading standard that can meet the needs of modern wireless networking, mainly offering energy efficiency and broad coverage as well as a massive amount of device support. In addition to the ALOHA protocol, which is the default channel access mechanism used by the standard, a number of alternatives have been proposed in the literature in an effort to ameliorate the overall network performance. Furthermore, with moving nodes gaining ground more and more in the IoT realm and the research being at a relatively premature stage, it is imperative to create innovative algorithms that support highly dense networks with fast moving nodes. Motivated by these reasons, this work proposes a novel medium access protocol that takes advantage of the increased capabilities of modern wake up radio (WuR) technology in order to achieve low latency and mitigate the risk of lost packets in IoT networks with moving nodes based on the LoRa technology. A number of simulation scenarios have been devised and the findings suggest that the proposed protocol achieves the set goals and improves existing solutions
Adaptive Spatial Scheduling for Event Traffic in LoRaWAN Networks
No full textLow-Power Wide-Area Networks constitute a leading, emerging Internet-of-Things technology, with important applications in environmental and industrial monitoring and disaster prevention and management. In such sensor networks, external detectable events can trigger synchronized alarm report transmissions. In LoRaWANs, and more generally in networks with a random access-based medium access algorithm, this can lead to a cascade of frame collisions, temporarily resulting in degraded performance and diminished system operational capacity, despite LoRaWANs’ physical layer interference and collision reduction techniques. In this paper, a novel scheduling algorithm is proposed that can increase system reliability in the case of such events. The new adaptive spatial scheduling algorithm is based on learning automata, as well as previous developments in scheduling over LoRaWANs, and it leverages network feedback information and traffic spatial correlation to increase network performance while maintaining high reliability. The proposed algorithm is investigated via an extensive simulation under a variety of network conditions and compared with a previously proposed scheduler for event-triggered traffic. The results show a decrease of up to 30% in average frame delay compared to the previous approach and an order of magnitude lower delay compared to the baseline algorithm. These findings highlight the importance of using spatial information in adaptive schemes for improving network performance, especially in location-sensitive applications
Reinforcement Learning in Traffic Prediction of Core Optical Networks using Learning Automata
No full textOn the use of prediction in Passive Optical LANs for healthcare latency-stringent applications
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