VoLTE: Fundamentals and Investment under Uncertainty by analogy with the Real Options Theory – A real case application in Greek Telecommunications market

Με την εμφάνιση των Τηλεπικοινωνιών, η φωνή έσπασε όλα τα φυσικά όρια και έγινε πραγματικότητα η μετάδοσή της παγκοσμίως σε πραγματικό χρόνο. Σύντομα, οι υπηρεσίες φωνής μετατράπηκαν σε βασική δραστηριότητα για τους παρόχους και το έναυσμα για την ανάπτυξη των Σταθερών και Κινητών Τηλεπικοινωνιών. Η τελευταία λέξη της τεχνολογίας για την Κινητή μετάδοση φωνής είναι το Voice over LTE (VoLTE), το οποίο αποτελεί μια σημαντική δυνατότητα του δικτύου για τη ουσιαστική βελτίωση της απόδοσης της φωνής και της χωρητικότητας του ραδιοδικτύου με ταυτόχρονη μείωση στα λειτουργικά κόστη. Στην παρούσα διπλωματική εργασία παρουσιάζονται οι βασικές αρχές της αρχιτεκτονικής VoLTE και παρέχεται μία ανάλυση της τεχνολογίας VoLTE ως επενδυτική ευκαιρία. Στο πρώτο μέρος παρατίθεται μια ιστορική αναδρομή σχετικά με την εξέλιξη των συστημάτων φωνής των Κινητής Τηλεπικοινωνιών από την πρώτη γενιά έως σήμερα. Περιλαμβάνεται μια επισκόπηση της αρχιτεκτονικής VoLTE με ανάλυση των κύριων υποσυστημάτων και των βασικών τους στοιχείων με βάση τις τεχνικές προδιαγραφές. Επιπλέον, παρουσιάζονται οι βασικές λειτουργίες μετάδοσης φωνής μέσω της τεχνολογίας VoLTE. Στο επόμενο μέρος περιγράφονται τα οφέλη και οι προκλήσεις που γεννιούνται από την ανάπτυξη της λύσης VoLTE, από τεχνικής άποψης αλλά και από πλευράς αγοράς. Για τον μετριασμό των κινδύνων, προτείνεται από τις χρηματοπιστωτικές αγορές η θεωρία των για την αξιολόγηση της επένδυσης, με βάση τη σύγχρονη βιβλιογραφία. Η ζήτηση της υπηρεσίας VoLTE μοντελοποιείται χρησιμοποιώντας τη γεωμετρική κίνηση Brown και αναπτύσσεται μια μεθοδολογία βασισμένη στα πραγματικά δικαιώματα προαίρεσης μέσω του δυναμικού προγραμματισμού, για τον υπολογισμό των βέλτιστων επενδυτικών κανόνων και του κόστους ευκαιρίας. Στο έκτο κεφάλαιο, παρουσιάζεται ένα παράδειγμα πραγματικής περίπτωσης επένδυσης VoLTE στην ελληνική αγορά Κινητών Τηλεπικοινωνιών, χρησιμοποιώντας την προτεινόμενη μεθοδολογία των πραγματικών δικαιωμάτων προαίρεσης. Τα αποτελέσματα συγκρίνονται με την παραδοσιακή προσέγγιση και αναλύονται με την χρήση προσομοιώσεων Monte Carlo. Συμπεράσματα και ενδιαφέροντα ευρήματα παρέχονται στο τελευταίο κεφάλαιο.With the emergence of Telecommunications, the voice broke all physical borders and could be transferred worldwide in real-time. Soon, voice services became a core business for the providers and the trigger for the development of Fixed and Mobile Telecommunications. The state of the art for mobile voice delivery is Voice over LTE (VoLTE), which is an important network capability to significantly improve the service performance and radio capacity while reducing operating costs. This study thesis presents the fundamental principles of VoLTE architecture and provides an analysis of the VoLTE solution as an investment opportunity. In the first part, a historical review is given regarding the evolution of the Cellular Mobile Telecommunication systems since their first generation. An overview of the VoLTE architecture is included with an analysis of the main subsystems and the core components based on the technical specifications. Moreover, the basic functionalities of the VoLTE technology are presented. The next part describes the benefits and challenges of deploying the VoLTE solution from technical and market perspectives. In order to mitigate the risks, the Real Options theory from the financial market is introduced for evaluating the VoLTE investment according to modern literature. The VoLTE demand is modelled using the Geometric Brownian Motion process and the dynamic programming is used to structure a Real Options-based framework for calculating optimal investment rules and opportunity cost. In the sixth chapter, a real case application of the proposed framework in the Greek Mobile Telecommunications market is presented. The results are compared with the traditional tools and analyzed by performing Monte Carlo simulations. Conclusions and interesting insights are provided in the last chapter

On SIP Server Clusters and the Migration to Cloud Computing Platforms

This thesis looks in depth at telephony server clusters, the modern switchboards at the core of a packet-based telephony service. The most widely used de facto standard protocols for telecommunications are the Session Initiation Protocol (SIP) and the Real Time Protocol (RTP). SIP is a signaling protocol used to establish, maintain, and tear down communication channel between two or more parties. RTP is a media delivery protocol that allows packets to carry digitized voice, video, or text. SIP telephony server clusters that provide communications services, such as an emergency calling service, must be scalable and highly available. We evaluate existing commercial and open source telephony server clusters to see how they differ in scalability and high availability. We also investigate how a scalable SIP server cluster can be built on a cloud computing platform. Elasticity of resources is an attractive property for SIP server clusters because it allows the cluster to grow or shrink organically based on traffic load. However, simply deploying existing clusters to cloud computing platforms is not good enough to take full advantage of elasticity. We explore the design and implementation of clusters that scale in real-time. The database tier of our cluster was modified to use a scalable key-value store so that both the SIP proxy tier and the database tier can scale separately. Load monitoring and reactive threshold-based scaling logic is presented and evaluated. Server clusters also need to reduce processing latency. Otherwise, subscribers experience low quality of service such as delayed call establishment, dropped calls, and inadequate media quality. Cloud computing platforms do not guarantee latency on virtual machines due to resource contention on the same physical host. These extra latencies from resource contention are temporary in nature. Therefore, we propose and evaluate a mechanism that temporarily distributes more incoming calls to responsive SIP proxies, based on measurements of the processing delay in proxies. Availability of SIP server clusters is also a challenge on platforms where a node may fail anytime. We investigated how single component failures in a cluster can lead to a complete system outage. We found that for single component failures, simply having redundant components of the same type are enough to mask those failures. However, for client-facing components, smarter clients and DNS resolvers are necessary. Throughout the thesis, a prototype SIP proxy cluster is re-used, with variations in the architecture or configuration, to demonstrate and address issues mentioned above. This allows us to tie all of our approaches for different issues into one coherent system that is dynamically scalable, is responsive despite latency varations of virtual machines, and is tolerant of single component failures in cloud platforms

JTIT

kwartalni

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen

Experiments in hydrologic solute transport

This thesis deal with experimental, field and modeling studies on reactive solute transport within hydrologic control volumes. The substances used in open environments for plant protection and other purposes are likely to be flushed by rainfall and enter into the hydrologic system if they are not disposed of through a sewage network. This represents a significant hazard for receiving ecosystems. The concentrations observed in surface waters are often highly dynamic, because of the variability of the hydrologic drivers controlling solute transport. This makes surface water monitoring particulary laborious, thus calling for a better understanding, and description of hydrologic transport at relevant spatial and temporal scales. The features of hydrologic transport are investigated under controlled conditions in a large weighing lysimeter, where all input (rainfall) and output (evapotranspiration and bottom discharge) fluxes are closely monitored. Random rainfall and large evapotranspiration (ET) fluxes dictated by two willows induce highly variable hydrologic conditions in the system. Fluorobenzoic acids (FBAs) as well as isotopically labeled water were used to unequivocally mark selected rainfall events. Chemical analyses were performed on samples of discharge and soil water collected through sampling ports in order to estimate the breakthrough curves of each tracer. Besides revealing unreported reactive behavior of the FBAs, these results demonstrate non stationary tracer responses that not only result from the transient precipitation forcing, but also from the variability in the ET-induced water deficits and how the output fluxes sample the water and solutes in storage under the prevalent moisture conditions. The experimental data were further explored using a model based on travel time distributions (TTDs). Describing hydrologic transport using TTDs is becoming increasingly common in catchment hydrology, because it allows a collective measurement of many processes (climate forcing, internal mixing, flow pathways, etc.) into a single stochastic descriptor, therefore removing the need to estimate numerous physical parameters and circumventing the limited applicability of point-scale laws for structurally complex and heterogenous environments. This parsimonious model is able to reproduce the different tracer responses by keeping track of the age composition of the stored water and assessing the ways ET and discharge sample the available water ages in time. The results emphasize the effects of ET on solute transport, because it samples water of different ages (i.e. residence times) in the transport volume in regards to discharge and thereby strongly modifies the resulting TTDs. In this way it is possible to compare the respective roles of the hydrologic variability and reactivity attributes (namely plant uptake and microbial degradation) which affect the tracer responses and prevent a direct interpretation of the experimental breakthrough curves as TTDs. \\ These experimental and modeled results highlight the importance of non stationary transport, often overlooked to interpret tracer data in catchment hydrology. This thesis demonstrates the benefits of tracer experiments towards the understanding of hydrologic systems undergoing reactive transport