<p>This thesis presents an analysis of the impact of node mobility on the quality of service for voice over Internet Protocol in wireless mesh networks. Voice traffic was simulated on such a mesh&nbsp / network to analyze the following performance metrics: delay, jitter, packet loss and throughput. Wireless mesh networks present interesting characteristics such as multi-hop routing, node mobility, and variable coverage that can impact on quality of service. A reasonable deployment scenario for a small organizational network, for either urban or rural deployment, is considered with three wireless mesh network scenarios, each with 26 mesh nodes. In the first scenario, all mesh nodes are stationary. In the second scenario, 10 nodes are mobile and 16 nodes are stationary.&nbsp / Finally, in the third scenario, all mesh nodes are mobile. The mesh nodes are simulated to move at a walking speed of 1.3m per second. The results show that node mobility can increase packet&nbsp / loss, delay, and jitter. However, the results also show that wireless mesh networks can provide acceptable quality of service, providing that there is little or no background traffic generated by other&nbsp / applications. In particular, the results demonstrate that jitter across all scenarios remains within humanacceptable tolerances. It is therefore recommended that voice over Internet Protocol implementations on wireless mesh networks with background traffic be supported by quality of service standards / otherwise they can lead to service delivery failures. On the other hand, voice-only&nbsp / esh networks, even with mobile nodes, offer an attractive alternative voice over Internet Protocol platform. </p>

This thesis work, conducted at Ericsson Software Research, aims to recommend a system setup for a tool to help troubleshooting personal at network operation centres (NOC) who monitors the telecom network. This thesis examines several different artificial intelligence algorithms resulting in the conclusion that Bayesian networks are suitable for the aimed system. Since the system will act as a decision support system it needs to be able to explain how recommendations have been developed. Hence a number of explanation methods have been examined. Unfortunately no satisfactory method was found and thus a new method was defined, modified explanation tree (MET) which visually illustrates the variables of most interest in a so called tree structure. The method was implementation and after some initial testing the method has gained some positive first feedback from stakeholders. Thus the final recommendation consists of a system based on a Bayesian model where the gathered training data is collected earlier from the domain. The users will thus obtain recommendations for the top ranked cases and afterwards get the option to get further explanation regarding the specific cause. The explanation aims to give the user situation awareness and help him/her in the final action to solve the problem.

The efficiency to which a wireless multi node network is connected is generally measured by the probability that all the nodes are connected to a master node or connected to a master node via other connected node. The grade of connectivity measures how easily and reliably a packet sent by a node can reach another node. Our thesis work is aimed to find connectivity measurement between the nodes in a wireless multi node network. The result is investigated by randomly placing all the nodes in a given area of 38*38 meters and by estimating the connectivity of the whole network. The sub goals of the thesis are To Design a link metric To Find a Routing algorithm which provides information about neighboring nodesAchieving the expected results from this thesis work, it can be a contribution to the research in the measure of connectivity for a wireless multi-node network. By using the available routing algorithm and by setting up appropriate threshold for (i) Good connectivity (ii) Average connectivity (iii) bad connectivity, the status (connectivity measure) is informed to the master node (teacher node) in the network, so that the life time of the whole network is enhanced. Various results and solutions are provided and discussed for the above stated problem from the practical experiments.

Measurement studies of Internet performance are critical for validating or refuting widely held beliefs about Web behavior, and for shedding light on unknown behaviors. Results from these studies can guide Internet architects in making decisions that affect Internet Service Providers (ISPs), content providers and end-users. Examples of decisions that can benefit from measurement information include provisioning network capacity, placing Domain Name System (DNS) and Web servers, and tuning parameters of transport layer protocols. Internet protocols and services may exhibit different performance characteristics when observed from different locations in the Internet topology; to date, however, there has been little work investigating the differences in these characteristics from multiple vantage points. Typically, performance studies present results of measurements taken in only one or two locations. Some of the reasons for the lack of work in this area are the following. First, performance measurement was not a high priority of Internet design and was not built into the network architecture. Second, it is difficult to obtain the necessary level of privilege at many different locations in the Internet topology to perform measurement studies. Finally, high expectations for real-time Internet performance is a relatively recent phenomenon. In this thesis we develop several methods for gathering Internet performance data from multiple locations throughout the world, and to analyze data gathered. Our focus is on the protocols and services that support the World Wide Web. In the first method we utilize a modified Web proxy. Our proxy captures and logs fine-grained performance information on a per-user basis. Our second method is to create and deploy a measurement package for examining DNS performance. We modified the BIND DNS server and packaged it with a script to drive the data collection. Our final method is to create and distribute an application to be run at user sites worldwide. One of the primary tasks of the application is to provide performance data from each instance of the application executing at locations throughout Internet topology. We can use the information provided by this application to examine user-perceived Internet performance throughout the globe.

In this dissertation, we study methods for improving the routing performance of computer communication networks in dynamic environments. The dynamic environments we considered in this work include both network topology changes and traffic demand changes. In the first part, We propose a novel fast rerouting scheme for link state routing protocols. Link state routing protocols are widely used by today’s ISPs on their backbone networks. The global update based rerouting of link state protocols usually takes seconds to complete which affects real time applications like Voice over IP. In our scheme, usually, only routers directly connected to failed links are involved in rerouting. For other cases, only a small number of neighboring routers are also involved. Since our scheme calculates rerouting paths in advance, rerouting can be done faster than previous reactive approaches. The computation complexity of our scheme is less than previous proactive approaches. In the second part, we study Multihoming Route Control (MRC) that is a technology used by multihomed stub networks recently. By selecting ISPs with better quality, MRC can improve routing performance of stub networks significantly. We first study the stability issue of distributed MRC and propose two methods to avoid possible oscillations of traditional MRC. The first MRC method is based on “optimal routing”. The idea is to let the stub networks belonging to a same organization coordinate their MRC and thus avoid oscillations. The second method is based on “user-optimal routing”. The idea is to allow MRC devices to use multiple paths for traffic to one destination network and switch traffic between paths smoothly when path quality or the traffic matrix changes. A third MRC method we propose is for MRC of traffic consisting of TCP flows of different sizes on paths with bottlenecks of limited capacity. Based on analysis of quality characteristics of bottleneck links, we propose a greedy MRC approach that works in small timescales. Simulation results show that the proposed MRC method can greatly improve routing performance for the MRC sites as well as the overall routing performance of all sites in the network.

In a Wireless Mesh Network (WMN) exists mobile nodes which have an unpredictable behaviour, i.e. they can join, leave and free move around the network. For this reason, a static network configuration is not proper for them. A distributed Dynamic Host Configuration Protocol (DHCP) is needed due to the unavailability of a centralized server in a network placed over a vast extension. This report shows a Distributed DHCP for WMNs using IPv6 (Internet Protocol version 6). It is fault tolerant, robust and durable. The algorithm was created using counters Bloom filters as data structure. After, a complete simulation of the system was done. The simulations showed that using 24 servers with 16Mbits of memory each one is possible to manage around 9000000 clients without adding an excessive network load. Therefore, the DDHCPv6 could be in a near future the host configuration protocol in WMN.

<p>This thesis presents an analysis of the impact of node mobility on the quality of service for voice over Internet Protocol in wireless mesh networks. Voice traffic was simulated on such a mesh&nbsp / network to analyze the following performance metrics: delay, jitter, packet loss and throughput. Wireless mesh networks present interesting characteristics such as multi-hop routing, node mobility, and variable coverage that can impact on quality of service. A reasonable deployment scenario for a small organizational network, for either urban or rural deployment, is considered with three wireless mesh network scenarios, each with 26 mesh nodes. In the first scenario, all mesh nodes are stationary. In the second scenario, 10 nodes are mobile and 16 nodes are stationary.&nbsp / Finally, in the third scenario, all mesh nodes are mobile. The mesh nodes are simulated to move at a walking speed of 1.3m per second. The results show that node mobility can increase packet&nbsp / loss, delay, and jitter. However, the results also show that wireless mesh networks can provide acceptable quality of service, providing that there is little or no background traffic generated by other&nbsp / applications. In particular, the results demonstrate that jitter across all scenarios remains within humanacceptable tolerances. It is therefore recommended that voice over Internet Protocol implementations on wireless mesh networks with background traffic be supported by quality of service standards / otherwise they can lead to service delivery failures. On the other hand, voice-only&nbsp / esh networks, even with mobile nodes, offer an attractive alternative voice over Internet Protocol platform. </p>

Wireless communications is a constantly progressing technology in network engineering society, creating an environment full of opportunities that are targeting in financial growth, quality of life and humans prosperity. Wireless security is the science that has as a goal to provide safe data communication between authorized users and prevent unauthorized users from gaining access, deny access, damage or counterfeit data in a wireless environment. In order to success it uses layers of protection that consist of software and hardware mechanisms that are able to monitor network’s behavior and in coordination provide a safe and secure environment for the user. In this thesis, a scientific research will be conducted in a given wireless network topology designed for an original application. This is about an intelligent street lightning system and it has already been implemented by Greinon Engineering which is the company that we are cooperating with. It is a matter of great importance that this thesis was conducted under real life criteria and in cooperation with an engineering company. This means that our programming, our ideas, our study research were all rotated and concentrated in certain type of hardware – software and network topology. In this thesis there is a detailed overview of basic wireless security mechanisms – vulnerabilities – types of attacks and countermeasures focused on 802.11b protocol. Moreover there will be security weak point’s analysis on the given industrial network; our proposals to protect and secure this network based on our threat analysis of the current system. There is an analysis on the most up to date VPN security implementations and reasoning that guided our team to conclude in a specific procedure - protocol and implementation, including limitation factors – obstacles faces during this procedure. During this research iterative approach in procedures – ideas and implementation attempts is followed. Basic goal is to provide security solutions that are easy applicable, low cost, easy to maintain and monitor.

Thesis (M.Eng.)(Electronic)--University of Pretoria, 2004. / Title from opening screen (viewed March 20, 2006). Summaries in English and Afrikaans. Includes bibliographical references.

München, Techn. University, Diss., 2000.