Many applications of wireless sensor networks (WSNs) require the sensor nodes of a network to belong to different priority classes where the nodes of a higher priority class enjoy higher data rates than nodes of a lower priority class. Practical design of such networks, however, faces challenges in satisfying the following basic design requirements: a) the need to rely on the medium access control mechanisms provided by the IEEE 802.15.4 standard for low-rate wireless personal area networks, b) the need to solve certain types of class size optimization problems to ensure adequate sensing coverage, and c) the need to achieve good utilization of the available channels. Unfortunately, the current version of the IEEE 802.15.4 does not provide adequate support for rate differentiation. Hence, many proposed solutions to the problem in the literature consider adding extensions to the standard. In this thesis, we introduce some class size optimization problems as examples of coverage problems that may arise in designing a WSN. We then consider a method proposed in the literature for handling the rate differentiation problem. The method relies on modifying the CSMA-CA channel access mechanism of the IEEE standard. We use simulation to examine its performance and its applicability to solve some class size optimization problems. We next investigate the use of Time Division Multiple Access (TDMA) protocols in providing service differentiation among different classes of sensors. We show simple sufficient conditions for the existence of TDMA-based solutions to a class size feasibility problem. Lastly, we consider the use of Guaranteed Time Slots (GTS) of the IEEE 802.15.4 standard in constructing TDMA schedules. We present a new algorithm that uses the GTS service to construct such schedules. The desired algorithm contains some optimization features. The obtained simulation results show the performance gain achieved by the algorithm.

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The emergence of large-scale Internet services coupled with the evolution of computing technologies such as distributed systems, parallel computing, utility computing, grid, and virtualization has fueled a movement toward a new resource provisioning paradigm called cloud computing. The main appeal of cloud computing lies in its ability to provide a shared pool of infinitely scalable computing resources for cloud services, which can be quickly provisioned and released on-demand with minimal effort. The rapidly growing interest in cloud computing from both the public and industry together with the rapid expansion in scale and complexity of cloud computing resources and the services hosted on them have made monitoring, controlling, and provisioning cloud computing resources at runtime into a very challenging and complex task. This thesis investigates algorithms, models and techniques for autonomously monitoring, controlling, and provisioning the various resources required to meet services’ performance requirements and account for their resource usage. Quota management mechanisms are essential for controlling distributed shared resources so that services do not exceed their allocated or paid-for budget. Appropriate cloud-wide monitoring and controlling of quotas must be exercised to avoid over- or under-provisioning of resources. To this end, this thesis presents new distributed algorithms that efficiently manage quotas for services running across distributed nodes. Determining the optimal amount of resources to meet services’ performance requirements is a key task in cloud computing. However, this task is extremely challenging due to multi-faceted issues such as the dynamic nature of cloud environments, the need for supporting heterogeneous services with different performance requirements, the unpredictable nature of services’ workloads, the non-triviality of mapping performance measurements into resources, and resource shortages. Models and techniques that can predict the optimal amount of resources needed to meet service performance requirements at runtime irrespective of variations in workloads are proposed. Moreover, different service differentiation schemes are proposed for managing temporary resource shortages due to, e.g., flash crowds or hardware failures. In addition, the resources used by services must be accounted for in order to properly bill customers. Thus, monitoring data for running services should be collected and aggregated to maintain a single global state of the system that can be used to generate a single bill for each customer. However, collecting and aggregating such data across geographical distributed locations is challenging because the management task itself may consume significant computing and network resources unless done with care. A consistency and synchronization mechanism that can alleviate this task is proposed.

With the explosive deployment of wireless LAN technology in the past few years and increasing demand on multimedia applications, the efficient utilization of the precious wireless radio link resources and support of Quality of Service (QoS) in WLANs has become a prominent research issue. In this thesis, an adaptive p-persistent based I 802.11 MAC scheme in WLANs has been proposed. The proposed scheme can maximize the total channel throughput, and also provide service differentiation among multiple traffic classes. This is achieved by updating the transmission probabilities for the stations that compete for transmissions in a WLAN, adaptively based on the real time network measurements. Extensive simulation experiments in ns-2 demonstrate that the proposed scheme is capable of achieving the system throughput bound and the target throughout ratios among different traffic stations in a dynamic WLAN environment. Also, the low computational complexity makes the proposed scheme a suitable choice for real-time implementation.

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Web servers become overloaded when one or several server resources such as network interface, CPU and disk become overutilized. Server overload leads to low server throughput and long response times experienced by the clients. Traditional server design includes only marginal or no support for overload protection. This thesis presents the design, implementation and evaluation of architectures that provide overload protection and service differentiation in web servers. During server overload not all requests can be processed in a timely manner. Therefore, it is desirable to perform service differentiation, i.e., to service requests that are regarded as more important than others. Since requests that are eventually discarded also consume resources, admission control should be performed as early as possible in the lifetime of a web transaction. Depending on the workload, some server resources can be overutilized while the demand on other resources is low because certain types of requests utilize one resource more than others. The implementation of admission control in the kernel of the operating system shows that this approach is more efficient and scalable than implementing the same scheme in user space. We also present an admission control architecture that performs admission control based on the current server resource utilization combined with knowledge about resource consumption of requests. Experiments demonstrate more than 40% higher throughput during overload compared to a standard server and several magnitudes lower response times. This thesis also presents novel architectures and implementations of operating system support for predictable service guarantees. The Nemesis operating system provides applications with a guaranteed communication service using the developed TCP/IP implementation and the scheduling of server resources. SILK (Scout in the Linux kernel) is a new networking stack for the Linux operating system that is based on the Scout operating system. Experiments show that SILK enables prioritizing and other forms of service differentiation between network connections while running unmodified Linux applications.

This thesis evaluates the performance of service differentiation with different class of services namely protection, reservation and the best effort services on the NxN meshed torus and the ring topology, which are established as survivable all&amp / #8208 / optical WDM networks. Blocking probabilities are measured as performance criteria and the effects of different number of wavelengths, different type of services and different topology size with wavelength selective lightpath allocation schemes are investigated by simulations with respect to increasing load on the topologies.

No description available.

Recently there has been a growing interest in the use of Low Rate Wireless Personal Area Networks (LR-WPAN) [1] driven by the large number of emerging applications such as home automation, health-care monitoring and environmental surveillance. To fulfill the needs for these emerging applications, IEEE has created a new standard called IEEE 802.15.4 for LR-WPAN, which has been widely accepted as the de facto standard for wireless sensor networks. Unlike IEEE 802.11 [2], which was designed for Wireless Local Area Networks (WLAN), it focuses on short range wireless communications. The goal of the IEEE 802.15.4 LR-WPAN is to support low data rate connectivity among wireless sensors with low complexity, cost and power consumption [3]. It specifies two types of network topologies, which are the beacon-enabled start network and the nonbeacon-enabled peer-to-peer network. For the beacon-enabled network, it defines the Guaranteed Time Slot (GTS) to provide real-time guaranteed service for delay-sensitive applications. In the nonbeacon-enabled network the GTS is reserved time slots such that it is requested, allocated and scheduled to wireless sensors that need guaranteed service for delay-sensitive applications. Existing GTS scheduling algorithms include First-Come-First-Served (FCFS) [1], priority-based [4] and Earliest Deadline First (EDF) [5] methods. Such FCFS and priority-based scheduling methods have critical drawbacks in achieving real-time guarantees. Namely, they fail to satisfy the delay constraints of delay-sensitive transactions. Further, they lead to GTS scarcity and GTS underutilization. On the other hand, the EDF-based scheduling method provides delay guarantee while it does not support delay-sensitive applications where arrival of the first packet has a critical impact on the performance. To solve these problems, we design the optimal work-conserving GTS Allocation and Scheduling (GAS) algorithm that provides guarantee service for delay-sensitive applications in beacon-enabled networks. Not only does the GAS satisfy the delay constraints of transactions, but also it reduces GTS scarcity and GTS underutilization. Further, it supports delay-sensitive applications where arrival of the first packet has a critical impact on the performance. Through the extensive simulation results, we show that the proposed algorithm outperforms the existing scheduling methods. Our algorithm differs from the existing ones in that it is an on-line scheduling and allocation algorithm and allows transmissions of bursty and periodic transactions with delay constraints even when the network is overloaded. In the nonbeacon-enabled peer-to-peer network some operating scenarios for rate-sensitive applications arise when one considers wireless video surveillance and target detection applications for wireless sensor networks. To support such rate-sensitive applications in wireless sensor networks, we present a Multirate-based Service Differentiation (MSD) operating in the nonbeacon-enabled peer-to-peer network. Unlike existing priority-based service differentiation models, the MSD defines the independent Virtual Medium Access Controls (VMACs), each of which consists of a transmission queue and the Adaptive Backoff Window Control (ABWC). Since the VMACs serve multiple rate-sensitive flows, it is possible that more than one data frame is collided with each other when their backoff times expire simultaneously. To solve such a virtual collision in the virtual collision domain, we design the Virtual Collision Avoidance Control (VCAC). The ABWC component adjusts the backoff window to reflect the local network state in the local collision domain. The VCAC component prevents virtual collisions and preempts packets with the minimal cost in the virtual collision domain. By analyzing these algorithms, we prove that the ABWC component enables the achieved data rate to converge to the rate requirement and the VCAC component produces a virtual-collision-free schedule to avoid degradation of the achieved data rate. Through the simulation, we validate our analysis and show the MSD outperforms existing algorithms. / Ph. D.

Telecommunication has evolved tremendously from its origin to the present. Competition has grown in the telecommunications industry. One of the idiosyncratic characteristics of the mobile telecom services industry is the offering of homogenous products/services to the whole market, which indicates services being undifferentiated. The purpose of this paper is to study the differentiation strategies of mobile telecom operators and the impact of factors influencing the process of differentiation. The study will concentrate on the differentiation strategies of the mobile telecom service firms operating in Pakistan. The analysis model of this research was developed based on the determinants of product differentiation, relating to the tools that managers at mobile telecom service companies employ to execute differentiation strategies, and the factors influencing them. The empirical part of this study was conducted in January 2017. The multiple case study approach was adopted as a study method, and four case studies of the mobile telecom service companies operating in Pakistan were compared through cross-case analysis. Qualitative methods of data collection were employed and through semi-structured interviews primary data was gathered and secondary data was extracted from the websites and annual reports. The findings from the four case studies revealed that all the mobile operators opt for the differentiation strategies based on the determinants. It was examined from this research that these determinants are interrelated with each other. It was evident from the study of all the case companies that regulations affect the industry profits, increase the cost of upgrading the networks and infrastructures, causing a delay in the adoption of innovation, thereby influencing the differentiation strategy. The second factor influencing the differentiation process revealed in this study was competitive imitation, which caused convergence of strategies resulting in undifferentiated services even though operators tried to differentiate their services. The competitive imitation becomes easier due to the oligopoly structure of the mobile telecom industry.