With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

Service composition is a process by which the services offered by devices may be combined to produce new, more complex services. In a pervasive computing environment where many devices exist and offer services, it is particularly desirable to fully automate this composition so end users do not need to be technically sophisticated. Earlier work done by Pourreza introduced a system to do fully automated service composition and to rank the services so produced by order of expected usefulness to the end user(s). My thesis research extends the work done by Pourreza in two ways. First, and most importantly, it adds support for services that have associated Quality of Service (QoS) characteristics. This allows me to ensure that I only generate composite services that are compatible in terms of the provided and required QoS characteristics of their component services. Further, it allows me to rank the generated composite services based on how well they meet the desired QoS preferences of users. Second, I extend Pourreza’s work by adding support for compositions involving services from outside a persistent computing environment (e.g. those provided via available Internet or 3G network access). I have built a prototype for the system to illustrate feasibility and to assess the overhead of supporting QoS in composition. I have also developed a regression model (based on collected user input regarding QoS preferences for services) that can be used to effectively rank compositions based on QoS for a variety of persistent environments. My results show that my approach is both feasible and effective.

Many of the grid compute resources (CPU cycles, network bandwidths, computing power, processor times, and software) exist as non-storable commodities, which we call grid compute commodities (gcc) and are distributed geographically across organizations. These organizations have dissimilar resource compositions and usage policies, which makes pricing grid resources and guaranteeing their availability a challenge. Several initiatives (Globus, Legion, Nimrod/G) have developed various frameworks for grid resource management. However, there has been a very little effort in pricing the resources. In this thesis, we propose financial option based model for pricing grid resources by devising three research threads: pricing the gcc as a problem of real option, modeling gcc spot price using a discrete time approach, and addressing uncertainty constraints in the provision of Quality of Service (QoS) using fuzzy logic. We used GridSim, a simulation tool for resource usage in a Grid to experiment and test our model. To further consolidate our model and validate our results, we analyzed usage traces from six real grids from across the world for which we priced a set of resources. We designed a Price Variant Function (PVF) in our model, which is a fuzzy value and its application attracts more patronage to a grid that has more resources to offer and also redirect patronage from a grid that is very busy to another grid. Our experimental results show that the application of the PVF has helped achieve equilibrium between users satisfaction measured as QoS and recovery of the infrastructure investment made by the providers. In the absence of pricing benchmarks, we setup Commodity Base Prices (CBP) and then integrated our PVF and CBP with GridSim to price grid compute resources. In summary, this thesis provides the design of a model to price grid compute resources using financial options theory. The model achieves mutual benefit for users and providers in the grid environment. The mutual benefit is expressed in terms of QoS to the users and recovery of investments on the grid infrastructure for the providers. This thesis has opened up many different opportunities for further research especially in the era of enterprise computing with clouds.

Consider the concept of the Utility Model [5]: the optimal allocation of resources of a server or network while meeting the absolute Quality of Service (QoS) requirements of users' multimedia sessions. Past algorithms and heuristics to solve the Utility Model mapped the problem onto a variant of the Combinatorial Knapsack Problem, with server utility (e.g. revenue) as the quantity to be optimized and with user QoS requirements expressed as constraints on the resource allocation. Both optimal (algorithmic) and fast but sub-optimal (heuristic) methods were derived to solve the resulting Multidimensional Multiconstraint Knapsack Problem (MMKP) and hence to perform admission control of proposed user sessions However, previous algorithms and heuristics were restricted to solving the Utility Model on an enterprise network (a network of less than 30 nodes), owing to the need in admission control to solve the problem in real time, typically a few seconds or less. The methods used for the path finding and admission processes had unfavorable computational complexities. As a result, only small (i.e. enterprise) networks could be treated in real time. Also, considerable time was wasted on frequently unnecessary traversals during upgrading. In this thesis we attempt to solve and implement the Utility Model using a modified version of a Multicommodity Flow algorithm, which has better computational complexity than Knapsack Algorithms or many heuristics and hence is capable of finding paths relatively quickly for larger networks. What's more, the Multicommodity flow algorithm used keeps essential information about the current networks and user sessions, thus further reducing the overall admission time.

Intelligent Transportation Systems (ITS) are gaining momentum among researchers. ITS encompasses several technologies, including wireless communications, sensor networks, data and voice communication, real-time driving assistant systems, etc. These states of the art technologies are expected to pave the way for a plethora of vehicular network applications. In fact, recently we have witnessed a growing interest in Vehicular Networks from both the research community and industry. Several potential applications of Vehicular Networks are envisioned such as road safety and security, traffic monitoring and driving comfort, just to mention a few. It is critical that the existence of convenience or driving comfort services do not negatively affect the performance of safety services. In essence, the dissemination of safety services or the discovery of convenience applications requires the communication among service providers and service requesters through constrained bandwidth resources. Therefore, service discovery techniques for vehicular networks must efficiently use the available common resources. In this thesis, we focus on the design of bandwidth-efficient and scalable service discovery protocols for Vehicular Networks. Three types of service discovery architectures are introduced: infrastructure-less, infrastructure-based, and hybrid architectures. Our proposed algorithms are network layer based where service discovery messages are integrated into the routing messages for a lightweight discovery. Moreover, our protocols use the channel diversity for efficient service discovery. We describe our algorithms and discuss their implementation. Finally, we present the main results of the extensive set of simulation experiments that have been used in order to evaluate their performance.

This thesis proposes a new algorithm for multi-constrained Quality of Service Optimal Path Routing in the context of military applications. The objective of our routing algorithm is to manage network traffic according to quality of service requirements of connection requests using military metrics. The algorithm is mainly based on communication priority. The QoS metrics such as bandwidth, delay and packet loss ratio are considered as basic metrics on path finding. If there is no suitable path for the request, some existing connections with lower priorities may be broken to make space for a higher priority level connection request. In this case, priority and bandwidth are used as decisive metrics in cost computation

隨著行動通訊日漸普及，愈來愈多使用者希望能夠在任何時間、任何地點，不受限制地使用他們所需的服務。但是由於IEEE 802.11通訊協定的限制，導致使用者無法獲得適當的服務品質保障，特別是使用者在享受即時性的服務，例如：網路電話、視訊會議、線上即時影音等。雖然在2001年IEEE提出802.11e草案，提供具有服務品質的無線通訊協定，但是在服務品質的效能方面表現並非完美，特別是在隨時變化的真實網路中。我們提出一個隨時根據網路狀況動態調整系統參數且容易實作並相容於IEEE 802.11e網路下的新機制。根據實驗模擬結果中，我們可以看到我們所提出的方法提供比EDCA更好的服務品質，就語音方面的延遲而言，我們減少約80%，就視訊方面的延遲，我們改善約25%，而輸出量方面約增加45%的效能，並且提高系統約6% - 40%最大的容納數。而我們也導入了允入控管，根據事先模擬的結果及設定的系統參數門檻，達到允入控管的目地，確保系統所提供的服務品質能夠滿足使用者的需求。 / Wireless LANs (WLANs) based on the IEEE 802.11 family have recently become popular for allowing high data rates at relatively low cost. However, due to the limitation of 802.11 DCF, they are not suitable for real-time service and do not support service differentiation. To expand providing applications with quality of service (QoS) requirements in WLANs, the IEEE 802.11E Task Group was formed to enhance the current 802.11 medium access control (MAC) protocol. In real networks, the network condition is dynamic. The 802.11e cannot reach high performance of QoS. Besides, design of efficient MAC protocols with both high-throughput and low-jitter performance is the major focus in distributed contention-based MAC protocol research. In view of this, we propose a new and applicable approach, called Dynamic-EDCA (D-EDCA), adjusts the parameters of system based on the network condition. The result of　simulation shows that in comparison with EDCA, our proposed algorithm improves total throughput more than 45%, and the maximum of connection more than 40%. It also reduces voice delay about 80%, and video delay about 25%. Thus, the proposed D-EDCA utilizes bandwidth more efficiently and improves performance for service differentiation.

Το VoIP (Voice Over IP) αναφέρεται στη μετάδοση και τη σηματοδοσία επικοινωνιών φωνής π.χ τηλεφωνικές κλήσεις πάνω από IP δίκτυα όπως είναι το διαδίκτυο. Σκοπός της παρούσας διπλωματικής ήταν η μελέτη της παρεχόμενης ποιότητας ομιλίας VoIP τηλεφωνικών συσκευών (Sitel,Polycom) κάτω από σενάρια διαφορετικών συνθηκών κίνησης στο δίκτυο. Αρχικά παρουσιάζονται οι εφαρμογές του voip και στη συνέχεια αναλύονται η λειτουργία, η αρχιτεκτονική και τα πρωτόκολλα της τεχνολογίας αυτής. Ακολούθως περιγράφεται η πειραματική διάταξη που απαιτήθηκε για να συγκεντρωθούν οι μετρήσεις από τις συσκευές και στη συνέχεια οι γραφικές αναπαραστάσεις των μετρήσεων αυτών που αφορούν της παρεχόμενη ποιότητα ομιλίας. Γίνεται ανάλυση των γραφικών και σύγκριση με ανάλογες της βιβλιογραφίας. / The VoIP technology refers to the transmission of voice samples over the Internet Protocol. The aim of the thesis is to investigate the QoS of a VoIP call under various networks circumstances when various impairments occur. The devices that we put under test belong to Sitel and Polycom company.

The popularity of wireless communication has increased substantially over the last decade, due to mobility support, flexibility and ease of deployment. Among next generation of mobile communication technologies, Ad Hoc networking plays an important role, since it can stand alone as private network, become a part of public network, either for general use or as part of disaster management scenarios. The performance of multihop Ad Hoc networks is heavily affected by interference, mobility, limited shared bandwidth, battery life, error rate of wireless media, and the presence of hidden and exposed terminals. The scheduler and the Medium Access Control (MAC) play a vital role in providing Quality of Service (QoS) and policing delay, end-to-end throughput, jitter, and fairness for user application services. This project aims to optimise the usage of the available limited resources in terms of battery life and bandwidth, in order to reduce packet delivery time and interference, enhance fairness, as well as increase the end-to-end throughput, and increase the overall network performance. The end-to-end throughput of an Ad Hoc network decays rapidly as the hop count between the source and destination pair increases and additional flows injected along the path of an existing flow affects the flows arriving from further away; in order to address this problem, the thesis proposes a Hop Based Dynamic Fair Scheduler that prioritises flows subject to the hop count of frames, leading to a 10% increase in fairness when compared to a IEEE 802.11b with single queue. Another mechanism to improve network performance in high congestion scenarios is network-aware queuing that reduces loss and improve the end-to-end throughput of the communicating nodes, using a medium access control method, named Dynamic Queue Utilisation Based Medium Access Control (DQUB-MAC). This MAC provides higher access probability to the nodes with congested queue, so that data generated at a high rate can be forwarded more effectively. Finally, the DQUB-MAC is modified to take account of hop count and a new MAC called Queue Utilisation with Hop Based Enhanced Arbitrary Inter Frame Spacing (QU-EAIFS) is also designed in this thesis. Validation tests in a long chain topology demonstrate that DQUB-MAC and QU-EAIFS increase the performance of the network during saturation by 35% and 40% respectively compared to IEEE 802.11b. High transmission power leads to greater interference and represents a significant challenge for Ad Hoc networks, particularly in the context of shared bandwidth and limited battery life. The thesis proposes two power control mechanisms that also employ a random backoff value directly proportional to the number of the active contending neighbours. The first mechanism, named Location Based Transmission using a Neighbour Aware with Optimised EIFS for Ad Hoc Networks (LBT-NA with Optimised EIFS MAC), controls the transmission power by exchanging location information between the communicating nodes in order to provide better fairness through a dynamic EIFS based on the overheard packet length. In a random topology, with randomly placed source and destination nodes, the performance gain of the proposed MAC over IEEE 802.11b ranges from approximately 3% to above 90% and the fairness index improved significantly. Further, the transmission power is directly proportional to the distance of communication. So, the performance is high and the durability of the nodes increases compared to a fixed transmission power MAC such as IEEE 802.11b when communicating distance is shorter. However, the mechanism requires positional information, therefore, given that location is typically unavailable, a more feasible power control cross layered system called Dynamic Neighbour Aware – Power controlled MAC (Dynamic NA -PMAC)is designed to adjust the transmission power by estimating the communicating distance based on the estimated overheard signal strength. In summary, the thesis proposes a number of mechanisms that improve the fairness amongst the competing flows, increase the end-to-end throughput, decrease the delay, reduce the transmission power in Ad Hoc environments and substantially increase the overall performance of the network.