Internet Access and QoS in Ad Hoc Networks

It is likely that the increased popularity of wireless local area networks (WLANs) together with the continuous technological advances in wireless communication, also increase the interest for ad hoc networks. An ad hoc network is a wireless, autonomous, infrastructure-less network composed of stations that communicate with each other directly in a peer-to-peer fashion. When discussing mobile ad hoc networks (MANETs), we often refer to an ad hoc network where the stations cooperate in forwarding packets on behalf of each other to allow communication beyond their transmission range over multi-hop paths. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed quality of service (QoS) guarantees and multi-hop Internet access. This thesis presents conceivable solutions to both of these problems. The first two papers focus on the network layer and consider the provisioning of Internet access to ad hoc networks whereas the last two papers focus on the data link layer and investigate the provisioning of QoS to ad hoc networks. The first paper studies the interconnection between a MANET and the Internet. In addition, it evaluates three approaches for gateway discovery, which can be initiated by the gateway (proactive method), by the mobile station (reactive method) or by mixing these two approaches (hybrid method). The second paper also studies Internet access for MANETs, but with focus on micro mobility, i.e. mobile stations moving from one gateway to another. In particular, it evaluates a solution that allows mobile stations to access the Internet and roam from gateway to gateway. The third paper, gives an overview of the medium access mechanisms in IEEE 802.11 and their QoS limitations. Moreover, it proposes an enhancement to the contention-free medium access mechanism of IEEE 802.11e to provide QoS guarantees in WLANs operating in ad hoc network configuration. The fourth paper continues the work from the third paper by enhancing the scheme and dealing with the problems that occur due to hidden stations. Furthermore, it discusses how to deal with the problems that occur when moving from single-hop ad hoc networks (i.e. WLANs in ad hoc network configuration) to multi-hop ad hoc networks

Supporting Internet Access and Quality of Service in Distributed Wireless Ad Hoc Networks

In this era of wireless hysteria, with continuous technological advances in wireless communication and new wireless technologies becoming standardized at a fast rate, we can expect an increased interest for wireless networks, such as ad hoc and mesh networks. These networks operate in a distributed manner, independent of any centralized device. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed QoS guarantees and multi-hop Internet access. In this thesis we present conceivable solutions to both of these problems. An autonomous, stand-alone ad hoc network is useful in many cases, such as search and rescue operations and meetings where participants wish to quickly share information. However, an ad hoc network connected to the Internet is even more desirable. This is because Internet plays an important role in the daily life of many people by offering a broad range of services. In this thesis we present AODV+, which is our solution to achieve this network interconnection between a wireless ad hoc network and the wired Internet. Providing QoS in distributed wireless networks is another challenging, but yet important, task mainly because there is no central device controlling the medium access. In this thesis we propose EDCA with Resource Reservation (EDCA/RR), which is a fully distributed MAC scheme that provides QoS guarantees by allowing applications with strict QoS requirements to reserve transmission time for contention-free medium access. Our scheme is compatible with existing standards and provides both parameterized and prioritized QoS. In addition, we present the Distributed Deterministic Channel Access (DDCA) scheme, which is a multi-hop extension of EDCA/RR and can be used in wireless mesh networks. Finally, we have complemented our simulation studies with real-world ad hoc and mesh network experiments. With the experience from these experiments, we obtained a clear insight into the limitations of wireless channels. We could conclude that a wise design of the network architecture that limits the number of consecutive wireless hops may result in a wireless mesh network that is able to satisfy users’ needs. Moreover, by using QoS mechanisms like EDCA/RR or DDCA we are able to provide different priorities to traffic flows and reserve resources for the most time-critical applications

Providing QoS Guarantees in Ad Hoc Networks through EDCA with Resource Reservation

As the use of WLANs based on IEEE 802.11 increase, the need for QoS becomes more obvious. The upcoming IEEE 802.11e aims at providing QoS, but its contention-based medium access mechanism enhanced distributed channel access (EDCA), provides only service differentiation, i.e. soft QoS. In order to provide hard QoS, we have proposed an extension called EDCA with resource reservation (EDCA/RR), which enhances EDCA by offering also hard QoS through resource reservation. This report focuses on EDCA/RR with the aim to enhance the scheme further in single-hop scenarios but also to present an idea of how to extend the scheme to be useful also in multi-hop ad hoc networks

An Enhancement to the IEEE 802.11e EDCA Providing QoS Guarantees

One of the challenges that must be overcome to realize the practical benefits of ad hoc networks is quality of service (QoS). However, the IEEE 802.11 standard, which undeniably is the most widespread wireless technology of choice for WLANs and ad hoc networks, does not address this issue. In order to support applications with QoS requirements, the upcoming IEEE 802.11e standard enhances the original IEEE 802.11 MAC protocol by introducing a new coordination function which has both contention-based and contention-free medium access methods. In this paper, we consider the contention-based medium access method, the EDCA, and propose an extension to it such that it can be used to provide QoS guarantees in WLANs operating in ad hoc mode. Our solution is fully distributed, uses admission control to regulate the usage of resources and gives stations with high-priority traffic streams an opportunity to reserve time for collision-free access to the medium

Traditional Practices for Sustainable Rangeland and Natural Resources Management: A Case Study of the Barzok Region, Iran

Livestock husbandry ranks second in importance the agricultural economy of Iran and also underpins the livelihood of many nomadic and sedentary peoples (Farhadi 2001). At the same time many rural locations such as the Bazok district have wide appeal to tourists because of cultural and natural features. This means local Iranian villagers must manage the grassland resources in a sustainable way according to geographical and climatic conditions. In general, utilization systems developed by local villages endeavour to combine social, cultural, economic and technical factors in such a way as to provide an optimal output of agricultural and eco-services (Papeli and Khanyeki 2001). The aim of this study was assess the role of traditional practices to sustain their grassland resources

Micro mobility and internet access performance for TCP connections in Ad Hoc networks

In ad hoc mobile networks nodes typically communicate over wireless channels and are capable of movement. These are networks that support multihop communication and can be formed on a temporary basis. This paper evaluates a solution that allows mobile nodes to access the wired Internet and roam from base station to base station. The solution is based on the extension of Mobile IP capabilities to the ad hoc network while a micro-mobility protocol is adapted to support local migration. We evaluate the performance of this solution with regard to reliable transport layer connections. It is shown that a high throughput is possible to achieve for high mobility speeds. It is also observed that, as the number of hops between a mobile node and the base station increases, the throughput is decreased because of the characteristics of the wireless environment and the medium access layer protocol

Family history of cardiovascular disease as a risk factor for coronary artery disease in adult offspring

Background and aims: There is controversy about the role of positive family history as an independent risk factor for coronary artery disease. The aim of this work was to investigate the influence of family history on presentation of coronary artery disease in adult offspring, and on its severity. Methods: In a retrospective cross-sectional study at Tehran Heart Center (University of Tehran Medical Sciences), 6399 patients with established coronary artery disease who underwent coronary angiography for standard indications were assessed. Coronary artery disease was defined as atherosclerotic involvement of more than 50% in at least one major coronary artery. Results: 953 patients (14.9%) had a verified positive family history of coronary artery disease, of whom 193 patients (20.2%) and 215 patients (22.5%) had paternal and maternal positive history, respectively. The mean age of clinical onset of ischemic heart disease in patients with a positive history was significantly lower than patients with no history (p < 0.001). Left main coronary lesion was significantly more frequent in patients with positive history (p = 0.017). Multivariate logistic regression analysis demonstrated that presentation of coronary artery disease in the form of acute coronary syndrome was significantly more prevalent in the background of positive family history (odds ratio, OR = 1.44, 95% confidence interval, CI: 1.14-1.83, p = 0.002), especially above 45 years old. Conclusion: These findings indicate that positive family history is a major risk factor for coronary artery disease which strongly predisposes to the atherosclerotic process at younger ages; therefore, these patients should be evaluated and managed more intensively for other risk factors

Evaluating and Ranking the Firms in Chemical Industry Listed in Tehran Stock Exchange with TOPSIS

Due to the sublimation and perfection of human knowledge in economics, the concept of efficiency developed in the past two decades and the measurement of it, based on different theories and practice. In economics, efficiency means the maximum of possible output from a certain amount of input. The efficiency is very important for developing countries Because these countries face to a shortage of inputs, production factors and technologies. So the usage of existing resources is critical for these countries. This paper aims to evaluate and rank the financial performance of the chemical firms listed in Tehran stock exchange. We Use the data environment analysis and TOPSIS methods. This research includes one major question that which company performs better due to the financial ratios. The sample includes the firms in Tehran Stock Exchange within a 3-year period (2013-2015). The Results show that Ahvas Petrochemical company, Persian Gulf Petrochemical Industry company and Iran Chemical Industries company are more efficient than others

The values and benefits of environmental elements on housing rents

© 2016 Elsevier Ltd. The value provided by availability of environmental elements on human quality of urban life is difficult to assess and incorporate into urban planning and development. Researchers worldwide have seldom objectively factored these attributes into property pricing and associated decisions. This study contends that a better understanding of the effect of environmental elements requires systematic study of the relationship between objective and subjective measures of environmental phenomena and human responses. This paper summarizes the outcomes from applying Hedonic Pricing (HP) and Life Satisfaction (LS) methods - providing valuation in an increasingly expanding and privatized property Iranian market. A survey was carried out from 400 households that are more likely to make location choices and pay rent and property expenses in the city of Shiraz. The findings indicates that Shiraz neighbourhoods are likely to be characterized by deep environmental segregation. This study informs the decisions of policy makers and property developers regarding sales and purchases conversion, property development, urban nature conservation, and design of ecological green-space networks