In der theoretischen Auseinandersetzung mit mobilen Internet-Diensten sind Quality of Service (QoS) und Quality of Experience (QoE) als hochkomplexe und verbundene Konzepte zu erkennen. QoS umfasst dabei die technische Sicht auf das Telekommunikationsnetz, charakterisiert durch leistungsrelevante Parameterwerte (z. B. Durchsatz und Latenz). QoE hingegen bezieht sich auf die Bewertung des Nutzererlebnisses (z. B. Zufriedenheit und Akzeptanz). Zur gemeinsamen Erklärung bedarf es einer multi- bzw. interdisziplinären Betrachtung zwischen Ingenieurs- und Humanwissenschaften, da neben der Technik auch der Mensch als Nutzer in den QoS-QoE-Zusammenhang involviert ist. Ein mehrschichtiges Modell erfasst die relevanten Einflussfaktoren und internen Zusammenhänge zwischen QoS und QoE sowohl aus Netz- als auch Nutzersicht. Zur Quantifizierung des Zusammenhangs konkreter Werte in einer empirischen QoE-Evaluation wurde ein umfangreiches psychophysikalisches Laborexperiment konzipiert. Das dafür entwickelte Netzemulations-Testbed erlaubt mobiltypische Netz- und Nutzungssituationen gezielt in einem Testparcours zusammenzubringen. Die formulierten Prinzipien zur Testrelevanz, -eignung und -effizienz berücksichtigen hierbei die Besonderheiten des Testaufbaus und -designs mit echten Endgeräten und Diensten. Die Ergebnisse von über 200 Probanden bestätigen die vorhergesagten QoS-QoE-Charakteristiken der sechs untersuchten Dienste als kontinuierlich-elastisch bzw. sprunghaft-fest. Dienstspezifisch lässt sich jeweils von einem angestrebten Grad der Nutzerzufriedenheit auf die notwendigen Werte der QoS-Netzparameter schließen, woraus sich ein QoS-QoE-Zufriedenheitskorridor zwischen einem unteren und oberen Schwellwert ergibt. Teilweise sind dabei QoS-unabhängige Faktoren, z. B. die Art der Präsentation der Stimuli in der App auf dem Endgerät, als ebenso relevant zu erkennen wie die QoS-Netzparameter selbst. / The thesis is centered on the relationship of Quality of Service (QoS) and Quality of Experience (QoE) for mobile Internet services. While QoS covers the technical view on the telecommunications network characterized by performance-related parameter values (e.g. throughput and latency), QoE refers to the assessment of the user experience (e.g. satisfaction and acceptability) in the use of the services. In the thesis QoS and QoE are revealed as highly complex and related concepts in theoretical contemplation. Integrating both concepts requires a multidisciplinary or interdisciplinary approach between engineering and human sciences to consider both - technological aspects of the network as well the human user. The designed multilayered model appropriately integrates the technical network view as well as the user's perspective by considering all relevant factors of influence and all internal relationships between QoS and QoE. The conducted extensive psychophysical laboratory experiment with real users, devices and services quantifies the relationship between specific QoS values and specific QoE values. A testbed developed for network emulation allows combining typical mobile network situations with typical usage situations in a controlled and focused manner. The three elaborated principles to test for relevance, suitability and efficiency take into account the special features of the test setup and test design. Test results gained from more than 200 volunteers confirm the predicted QoS-QoE-characteristics of the six tested mobile services to be either elastic or non-elastic. It is possible to conclude from the desired degree of user satisfaction on the necessary values of the QoS network parameters, which results in a QoS-QoE-corridor between lower and upper threshold values. Findings prove that QoS-independent factors, e.g. the type of presentation of the stimuli in the app on the user’s device, can be as relevant for QoE as the evaluated QoS network parameters themselves.

The growing demand on the variety of internet applications requires management of large scale networks by efficient Quality of Service (QoS) routing, which considerably contributes to the QoS architecture. The biggest contemporary drawback in the maintenance and distribution of the global state is the increase in communication overheads. Unbalancing in the network, due to the frequent use of the links assigned to the shortest path retaining most of the network loads is regarded as a major problem for best effort service. Localised QoS routing, where the source nodes use statistics collected locally, is already described in contemporary sources as more advantageous. Scalability, however, is still one of the main concerns of existing localised QoS routing algorithms. The main aim of this thesis is to present and validate new localised algorithms in order to develop the scalability of QoS routing. Existing localised routing, Credit Based Routing (CBR) and Proportional Sticky Routing (PSR), use the blocking probability as a factor in selecting the routing paths and work with either credit or flow proportion respectively, which makes impossible having up-to-date information. Therefore our proposed Highest Minimum Bandwidth (HMB) and Highest Average Bottleneck Bandwidth History (HABBH) algorithms utilise bandwidth as the direct QoS criterion to select routing paths. We introduce an Integrated Delay Based Routing and Admission Control mechanism. Using this technique Minimum Total Delay (MTD), Low Fraction Failure (LFF) and Low Path Failure (LPF) were compared against the global QoS routing scheme, Dijkstra, and localised High Path Credit (HPC) scheme and showed superior performance. The simulation with the non-uniformly distributed traffic reduced blocking probability of the proposed algorithms. Therefore, we advocate the algorithms presented in the thesis, as a scalable approach to control large networks. We strongly suggest that bandwidth and mean delay are feasible QoS constraints to select optimal paths by locally collected information. We have demonstrated that a few good candidate paths can be selected to balance the load in the network and minimise communication overhead by applying the disjoint paths method, recalculation of candidate paths set and dynamic paths selection method. Thus, localised QoS routing can be used as a load balancing tool in order to improve the network resource utilization. A delay and bandwidth combination is one of the future prospects of our work, and the positive results presented in the thesis suggest that further development of a distributed approach in candidate paths selection may enhance the proposed localised algorithms.

近十年來，由於無線網路的普及與人們對於即時服務的需求提高，導致人們迫切需要更好的服務品質，WiMAX是其中最被看好的一種無線網路傳輸技術。但在WiMAX無線網路中，標準的規格中並未規範connection admission control (CAC)、bandwidth request (BR)、bandwidth allocation、scheduling等機制，在本篇論文中，我們將上述機制設計並實作於MAC layer中。 本論文首先探討在設計connection admission control、bandwidth request、bandwidth allocation、scheduling會遇到的相關參數及相關議題。並進一步提出一個有效的方法以改善目前大部分設計在bandwidth allocation的公平性 (Fairness)及contention bandwidth request等效率差的問題。我們將設計一個MAC Layer co-function，稱之為Dynamic Polling Interval function (DPI function)。利用DPI function設計no contention bandwidth request改善傳統 contention bandwidth request的效率，以及利用DPI function的特性改善bandwidth allocation以及scheduling的公平性。最後我們將利用網路模擬器NS-2 (Network Simulater version 2)與測試實驗架構作不同效能的驗證比較並評估所提方法的有效性。 / Over the past decade, wireless network access and real-time services have become more popular than ever. People are eager to have better quality of service. Among all, WiMAX is one of the best wireless communication technigues . However, WiMAX standard does not specify those mechanisms of connection admision control (CAC)、bandwidth request (BR)、bandwidth allocation and scheduling . In this thesis, we propose the above mechanisms and imcorporate them as MAC layer functions. First, we discuss those related parameters and issues when designing connection admision control、bandwidth request、bandwidth allocation and scheduling. Second, we propose an efficient method to improve the fairness of bandwidth allocation and efficiency of contention bandwidth request. We design a MAC layer co-function called dynamic polling interval function (DPI function). We use the DPI function to design a no contention bandwidth request method to improve the efficiency of traditional bandwidth request method and use the features of DPI function to improve the fairness of bandwidth allocation and scheduling. At last , we use NS-2 (Network Simulator version 2) as our network simulator and compare the result of simulations to prove the efficiency of our proposed methods.

The exponential growth of Internet applications has created new challenges for the control and administration of large-scale networks, which consist of heterogeneous elements under dynamically changing traffic conditions. These emerging applications need guaranteed service levels, beyond those supported by best-effort networks, to deliver the intended services to the end user. Several models have been proposed for a Quality of Service (QoS) framework that can provide the means to transport these services. It is desirable to find efficient routing strategies that can meet the strict routing requirements of these applications. QoS routing is considered as one of the major components of the QoS framework in communication networks. In QoS routing, paths are selected based upon the knowledge of resource availability at network nodes and the QoS requirements of traffic. Several QoS routing schemes have been proposed that differ in the way they gather information about the network state and the way they select paths based on this information. The biggest downside of current QoS routing schemes is the frequent maintenance and distribution of global state information across the network, which imposes huge communication and processing overheads. Consequently, scalability is a major issue in designing efficient QoS routing algorithms, due to the high costs of the associated overheads. Moreover, inaccuracy and staleness of global state information is another problem that is caused by relatively long update intervals, which can significantly deteriorate routing performance. Localized QoS routing, where source nodes take routing decisions based solely on statistics collected locally, was proposed relatively recently as a viable alternative to global QoS routing. It has shown promising results in achieving good routing performance, while at the same time eliminating many scalability related problems. In localized QoS routing each source-destination pair needs to determine a set of candidate paths from which a path will be selected to route incoming flows. The goal of this thesis is to enhance the scalability of QoS routing by investigating and developing new models and algorithms based on the localized QoS routing approach. For this thesis, we have extensively studied the localized QoS routing approach and demonstrated that it can achieve a higher routing performance with lower overheads than global QoS routing schemes. Existing localized routing algorithms, Proportional Sticky Routing (PSR) and Credit-Based Routing (CBR), use the blocking probability of candidate paths as the criterion for selecting routing paths based on either flow proportions or a crediting mechanism, respectively. Routing based on the blocking probability of candidate paths may not always reflect the most accurate state of the network. This has motivated the search for alternative localized routing algorithms and to this end we have made the following contributions. First, three localized bandwidth-constrained QoS routing algorithms have been proposed, two are based on a source routing strategy and the third is based on a distributed routing strategy. All algorithms utilize the quality of links rather than the quality of paths in order to make routing decisions. Second, a dynamic precautionary mechanism was used with the proposed algorithms to prevent candidate paths from reaching critical quality levels. Third, a localized delay-constrained QoS routing algorithm was proposed to provide routing with an end-to-end delay guarantee. We compared the performance of the proposed localized QoS routing algorithms with other localized and global QoS routing algorithms under different network topologies and different traffic conditions. Simulation results show that the proposed algorithms outperform the other algorithms in terms of routing performance, resource balancing and have superior computational complexity and scalability features.

Este trabalho propõe políticas para servidores Web baseados em sessões, visando ao oferecimento de garantias de qualidade de serviço (Quality of Service - QoS) a seus usuários. Para o fornecimento de QoS, dois tipos de políticas são consideradas: as responsáveis pela diferenciação de serviços e as responsáveis pelo controle de admissão. Alguns algoritmos de escalonamento foram desenvolvidos com o objetivo de oferecer melhores serviços para as sessões prioritárias: o algoritmo de escalonamento baseado em sessão (SBSA) e o algoritmo de escalonamento baseado em sessão com diferenciação de serviços (SBSA-DS). Quanto ao controle de admissão, foram consideradas duas novas políticas, as quais utilizam diferentes parâmetros para a tomada de decisão e têm como objetivo garantir a finalização do maior número de sessões prioritárias. A partir dos resultados obtidos nos experimentos realizados por meio de simulação, constatou-se que o emprego dos algoritmos e das políticas desenvolvidos melhora o atendimento das sessões para as quais deve ser oferecido um serviço preferencial. Portanto, em servidores Web preocupados com a garantia de QoS para seus usuários, os quais interagem com o sistema por meio de sessões, o uso dessas novas técnicas se mostra adequado / This work considers policies for Web servers based on sessions, aiming at the guarantees of Quality of Service (QoS) to the systems users. Two types of policies are considered: the responsible for the differentiation of services and the responsible for the admission control. Some scheduling algorithms had been developed to offer better services for the priority sessions: the Session Based Scheduling Algorithm (SBSA) and the Session Based Scheduling Algorithm with Differentiation of Services (SBSA-DS). In relation to the admission control, two new policies had been considered, which use different parameters to help the decisions and have as objective guarantee the finalization of as many priority sessions as possible. From the obtained results of the experiments realized by mean of simulation, it is evidenced that the use of the developed algorithms and policies improves the attendance of the sessions that deserve preferential service. Therefore, in Web servers worried in the guarantee the QoS for their users, which interact with the system by sessions, the use of these new techniques reveals adequate

In this thesis, focusing on the quality of service (QoS) improvement using per-packet power control algorithm in Ad Hoc Cognitive Packet Networks (AHCPN). A power control mechanism creates as a network-assisted function of ad hoc cognitive packet-based routing and aims at reducing both energy consumption in nodes and QoS requirements. The suggested models facilitate transmission power adjustments while also taking into account the effects on network performance. The thesis concentrate on three main contributions. Firstly, a power control algorithm, namely the adaptive Distributed Power management algorithm (DISPOW) was adopted. Performance of DISPOW was compared to existing mechanisms and the results showed 27, 13, 9, and 40 percent improvements in terms of Delay, Throughput, Packet Loss, and Energy Consumption respectively. Secondly, the DISPOW algorithm was enhanced, namely a Link Expiration Time Aware Distributed Power management algorithm (LETPOW). This approach periodically checks connectivity, transmission power, interference level, routing overhead and Node Mobility in AHCPN. The results show that LETPOW algorithm improves the performance of system. Results show further improvement from DISPOW by 30,25,30,42 percent in terms of delay, packet loss ratio , path lengths and energy consumption respectively. Finally,Hybrid Power Control Algorithm (HLPCA) has presented is a combination of Link Expiration Time Aware Distributed Power management algorithm (LETPOW) and Load Power Control Algorithm (LOADPOW); deal with cross-layer power control applied for transmitting information across the various intermediate layers. LOADPOW emphasis on the concept of transmission Power, Received Signal Strength Indication (RSSI), and the suitable distance between the receiver and the sender. The proposed algorithm outperforms DISPOW and LETPOW by 31,15,35,34,44 percent in terms of Delay, Throughput, Packet Loss,path length and Energy Consumption respectively. From this work, it can be concluded that optimized power control algorithm applied to Ad-hoc cognitive packet network results in significant improvement in terms of energy consumption and QoS.

Today, telecommunication is improving rapidly. People are online anywhere anytime. Due to increasing demand in communication, wireless technologies are progressing quickly trying to provide more services in a wide range. In order to address mobility and connectivity requirements of users in wide areas, Worldwide Interoperability for Microwave Access (Wimax) has been introduced as a forth generation telecommunication technology. Wimax, which is also called Metropolitan Area Network (MAN), is based on IEEE 802.16 standard where a Base Station (BS) provides last mile broadband wireless access to the end users known as Mobile Stations (MS). However, in places where high constructions exist, the signal rate between MS and BS decreases or even the signal can be lost completely due to shadow fading. As a response to this issue, recently an intermediate node specification, namely Relay Station, has been defined in IEEE 802.16j standard for relaying, which provides both throughput enhancement and coverage extension. However, this update has introduced a new problem / call admission control in non-transparent relay networks that support coverage extension. In this thesis, a Quality of Service (QoS) aware dynamic admission control algorithm for IEEE 802.16j non-transparent relay networks is introduced. Our objectives are admitting more service flows, utilizing the bandwidth, giving individual control to each relay station (RS) on call acceptance and rejection, and finally not affecting ongoing service flow quality in an RS due to the dense population of service flows in other RSs. The simulation results show that the proposed algorithm outperforms the other existing call admission control algorithms. Moreover, this algorithm can be interpreted as pioneer call admission control algorithm in IEEE 802.16j non-transparent networks.

Web Service technology is one of the most rapidly developing contemporary technologies. Nowadays, Web Services are being used by a large number of projects and academic studies all over the world. As the use of Web service technology is increasing, it becomes harder to find the most suitable web service which meets the Quality of Service (QoS) as well as functional requirements of the user. In addition, quality of the web services (QoS) that take part in the software system becomes very important. In this thesis, we develop a method to track the QoS primitives of Web Services and an algorithm to automatically calculate QoS values for Web Services. The proposed method is realized within a domain specific web service discovery system, namely DSWSD-S, Domain Specific Web Service Discovery with Semantics. This system searches the Internet and finds web services that are related to a domain and calculates QoS values through some parameters. When a web service is queried, our system returns suitable web services with their QoS values. How to calculate, keep track of and store QoS values constitute the main part of this study.

Traditionally the Internet is used for the following applications: FTP, e-mail and Web traffic. However in the recent years the Internet is increasingly supporting emerging applications such as IP telephony, video conferencing and online games. These new applications have different requirements in terms of throughput and delay than traditional applications. For example, interactive multimedia applications, unlike traditional applications, have more strict delay constraints and less strict loss constraints. Unfortunately, the current Internet offers only a best-effort service to all applications without any consideration to the applications specific requirements. In this thesis three existing Active Queue Management (AQM) mechanisms are modified by incorporating into these a control function to condition routers for better Quality of Service (QoS). Specifically, delay is considered as the key QoS metric as it is the most important metric for real-time multimedia applications. The first modified mechanism is Drop Tail (DT), which is a simple mechanism in comparison with most AQM schemes. A dynamic threshold has been added to DT in order to maintain packet queueing delay at a specified value. The modified mechanism is referred to as Adaptive Drop Tail (ADT). The second mechanism considered is Early Random Drop (ERD) and, iii in a similar way to ADT, a dynamic threshold has been used to keep the delay at a required value, the main difference being that packets are now dropped probabilistically before the queue reaches full capacity. This mechanism is referred to as Adaptive Early Random Drop (AERD). The final mechanism considered is motivated by the well known Random Early Detection AQM mechanism and is effectively a multi-threshold version of AERD in which packets are dropped with a linear function between the two thresholds and the second threshold is moveable in order to change the slope of the dropping function. This mechanism is called Multi Threshold Adaptive Early Random Drop (MTAERD) and is used in a similar way to the other mechanisms to maintain delay around a specified level. The main focus with all the mechanisms is on queueing delay, which is a significant component of end-to-end delay, and also on reducing the jitter (delay variation) A control algorithm is developed using an analytical model that specifies the delay as a function of the queue threshold position and this function has been used in a simulation to adjust the threshold to an effective value to maintain the delay around a specified value as the packet arrival rate changes over time. iv A two state Markov Modulated Poisson Process is used as the arrival process to each of the three systems to introduce burstiness and correlation of the packet inter-arrival times and to present sudden changes in the arrival process as might be encountered when TCP is used as the transport protocol and step changes the size of its congestion window. In the investigations it is assumed the traffic source is a mixture of TCP and UDP traffic and that the mechanisms conserved apply to the TCP based data. It is also assumed that this consists of the majority proportion of the total traffic so that the control mechanisms have a significant effect on controlling the overall delay. The three mechanisms are evaluated using a Java framework and results are presented showing the amount of improvement in QoS that can be achieved by the mechanisms over their non-adaptive counterparts. The mechanisms are also compared with each other and conclusions drawn.

Η οπτική μεταγωγή ριπών (Optical Burst Switching-OBS) στοχεύει στον συνδυασμό των πλεονεκτημάτων της οπτικής μεταγωγής πακέτων και μεταγωγής κυκλώματος. Θεωρείται ως μια αρκετά υποσχόμενη τεχνολογία για την υλοποίηση του οπτικού Διαδικτύου της επόμενης γενιάς, με σκοπό να αντεπεξέλθει στην ταχεία ανάπτυξη της κίνησης του Διαδικτύου και στην αυξανόμενη υιοθέτηση νέων υπηρεσιών (π.χ VoIP τηλεφωνία, βίντεο κατά απαίτηση, υπολογισμός πλέγματος, ψηφιακά αποθηκευτικά μέσα). Στα OBS δίκτυα, τα πακέτα συναρμολογούνται σε ριπές και στέλνονται έτσι διαμέσου του δικτύου. Επομένως, ο τρόπος με τον οποίο πραγματοποιείται η συναρμολόγηση των πακέτων σε ριπές, καθορίζει και τα χαρακτηριστικά του συνολικού δικτύου και επηρεάζει κυρίως την συνολική καθυστέρηση του κάθε πακέτου που στέλνεται διαμέσου αυτού. Στην παρούσα εργασία (μέρος της διπλωματικής εργασίας δημοσιεύτηκε στο [21]), θα προτείνουμε τέσσερις νέες τεχνικές συναρμολόγησης ριπών που στοχεύουν στην μείωση της μέσης καθυστέρησης που επιβαρύνονται τα πακέτα κατά τη διαδικασία της συναρμολόγηση τους σε ριπές (burstification), με βάση ενός δεδομένου μέσου μήκους των ριπών που παράγονται. Αυτές οι τεχνικές χρησιμοποιούν ένα γραμμικό φίλτρο πρόβλεψης για την παραγωγή μιας εκτίμησης του πλήθους των πακέτων που πρόκειται να εισέλθουν στο κόμβο του δικτύου, που λαμβάνει χώρα το burstification, κατά τη διάρκεια της επόμενης χρονικής περιόδου. Με βάση την εκτίμηση αυτή, αποφασίζουν αν ικανοποιείται ένα συγκεκριμένο κριτήριο, το οποίο είναι διαφορετικό για κάθε προτεινόμενη μέθοδο, και στέλνουν, αναλόγως, μία νέα ριπή στο δίκτυο. Η μείωση της καθυστέρησης της συναρμολόγησης των πακέτων, για ένα δεδομένο μέσο μήκος ριπής, είναι σημαντική για τις εφαρμογές πραγματικού χρόνου, οι οποίες έχουν αυστηρούς περιορισμούς στην συνολική καθυστέρηση των πακέτων. Αντίστοιχα, η αύξηση του μέσου μήκους των ριπών που δημιουργούνται σε ένα OBS δίκτυο, για μια δεδομένη μέση καθυστέρηση πακέτων, είναι σημαντική για την μείωση του αριθμού των ριπών που εισέρχονται σε αυτό. Μεγάλου μήκους ριπές συνεπάγονται μικρότερη επιβάρυνση σε επεξεργασία που διενεργείται από τους ενδιάμεσους κόμβους του δικτύου. Επίσης, στο παρόν κείμενο, θα αξιολογήσουμε την συμπεριφορά των προτεινόμενων τεχνικών συναρμολόγησης και θα αποδείξουμε ότι δύο από αυτές έχουν καλύτερη απόδοση (έως και 33% βελτίωση), σε σύγκριση με τους προηγουμένως προτεινόμενους από την βιβλιογραφία αλγόριθμους, ως προς την μέση καθυστέρηση πακέτων, για δεδομένο μήκος ριπής. Τέλος, θα συζητηθεί η δυνατότητα παροχής ποιότητας υπηρεσιών (Quality of Service- QoS) με την βοήθεια των προτεινόμενων αλγορίθμων συναρμολόγησης. Το υπόλοιπο του παρόντος κειμένου είναι οργανωμένο με βάση τα παρακάτω: • Το δεύτερο κεφάλαιο σχολιάζει βασικές έννοιες των οπτικών δικτύων και περιγράφει την αρχιτεκτονική των οπτικών δικτύων μεταγωγής ριπών. • Το τρίτο κεφάλαιο αναφέρεται στις ήδη προτεινόμενες τεχνικές συναρμολόγησης ριπών, από την υπάρχουσα βιβλιογραφία. • Στο τέταρτο κεφάλαιο, σχολιάζονται σημαντικές έννοιες των γραμμικών προβλεπτών, καθώς κι η δυνατότητα τους να εφαρμοστούν στην πρόβλεψη της κίνησης του δικτύου και υπό ποιες συνθήκες η χρήση τους είναι αποδοτική. • Οι προτεινόμενοι αλγόριθμοι περιγράφονται στο πέμπτο κεφάλαιο. • Στο έκτο κεφάλαιο εξετάζεται η απόδοση τους σε σχέση με τους υπάρχοντες αλγορίθμους και μελετάται η συμπεριφορά του επιλεγμένου γραμμικού προβλεπτή σε σχέση με τις παραμέτρους εισόδου που τον χαρακτηρίζουν. • Τέλος στο έβδομο κεφάλαιο, περιγράφεται η παροχή του QoS στο δίκτυο και ερευνάται η δυνατότητα υποστήριξης της, με τη βοήθεια των προτεινόμενων τεχνικών συναρμολόγησης. / -