Graduated PhDs
Anne Nevin
The Uncertainty of Decisions in Measurement Based Admission Control
2010-11-22
Most real-time voice and video applications are delay/loss sensitive but relaxed in the sense that they can tolerate some packet loss/delay. Using this information, network utilization can be greatly improved by exploiting statistical multiplexing.
To this end, Measurement Based Admission Control (MBAC) has for a long time been recognized as a promising solution. MBAC algorithms, do not require an a priori source characterization which in many cases may be difficult or impossible to attain. Instead, MBAC uses measurements to capture the behavior of existing flows and uses this information together with some coarse knowledge of a new flow when making an admission decision for this requesting flow.
Kjetil Haslum
Real-time Network Intrusion Prevention
2010-10-14
It is not economically or technically feasible to make complex computer systems that are completely secure. New attacks are constantly developed by attackers and the security situation can therefore rapidly change. In order to detect and stop attackers before any damage is done, automated tools have to be deployed because there is not enough time for manual intervention. Therefore there is a need for online risk assessment and proactive defense mechanisms like Intrusion Prevention System (IPS). In the area of computer security there have been only a few quantitative security measures until now, and there are few published cases for methods and tools based on such measures.
Erik Hellerud
Transmission of High Quality Audio over IP Networks
2009-10-02
This thesis deals with the transmission of high quality audio over packet switched networks, such as the internet. Unlike other transmission media, no guarantees are given regarding bandwidth, delay, or loss ratios, and all these factors will typically be time-varying. For interactive, or two-way, applications it is important to keep a low end-to-end delay in order to have a high Quality of Experience. In this scenario, retransmission of lost packets is not possible simply due to the delay restrictions, thus one has to expect and prepare for periods with packet loss.
Tor Kjetil Moseng
A QoS Architecture for Mobile Ad Hoc Networks
2009-06-19
In this thesis the Differentiated Services (DiffServ) architecture is applied and adapted to Mobile Ad Hoc Networks (MANETs). Using the same QoS architecture will ease the transition between the wireless and wired domain. But the special characteristics of wireless networks require modifications to the original DiffServ architecture. In investigations there was found restrictions on the number of classes to use, and this number was dependent on the type of traffic in the network. A QoS architecture based on the DiffServ framework is proposed, with an admission control based on the concept of shadow classes, and Explicit Congestion Notification (ECN) to avoid congestion.
Marie Elisabeth Gaup Moe
Security, Privacy and Trust in Dynamic Networks
2009-06-02
Abstract Emergent networks like mobile ad hoc networks, sensor networks, opportunistic networks, peer-to-peer networks and social networks are introducing new and exciting opportunities of communication between people and devices. But these dynamic networks also introduce many security- and privacy-related challenges. When dealing with complex and dynamic environments, information about the current level of security or privacy, expressed in a quantified manner, could be of great value in a decision-making process. In order to derive such quantified measures there is a need for mathematical models for security, privacy and trust. The development, application and evaluation of such models are the topics of this thesis.
Astrid Undheim
Characterization and Modeling of Slice-based Video Traffic
2009-05-27
The interest in watching real-time video content transmitted over packet-based communication networks such as the Internet is growing. When resources are restricted, quality of service support and provisioning of service guarantees are needed in the network to ensure a satisfactory user experience. In addition, the video content, different choices made in the video encoding, the bitrate characteristics of the resulting video stream, and the network performance will have an influence on the perceived quality. Regarding the network performance, the packet loss ratio and packet loss distribution are identified as important performance parameters for real-time video, and are of particular interest. Estimating these parameters is a step towards assessing the perceived quality of service for a video transmission.
Yuan Lin
Resource Allocation through Encoding Algorithms for Real-time Video Communications
2009-03-03
In this dissertation, we are focusing on error resilient resource allocation through encoding algorithms in real-time video communications. The thesis is composed of six papers which are grouped into two parts with each part addressing a specific type of communication scenario.
Dr. Yuan Lin is now working at Nera in Bergen, Norway.
Audun Solvang
Representation of High Quality Spatial Audio
2009-01-29
Classical surround sound techniques are based on sweet spot listening while sound field approaches offer higher quality in that they can give reproduction over an extended area. The expenses are higher complexity in the creation and reproduction of the audio content and a high bit rate. The fact that we perceive the direct sound, early reflections and the late part of a room impulse response differently forms the basis for contemporary hybrid formats that can yield a lower bit rate. These formats are, however, based on classical surround sound techniques and are meant for for sweet spot listening. This thesis looks into both sound field reproduction that can be used for direct sound reproduction and the reproduction of the late diffuse part of a room impulse response.
Dr. Audun Solvang is now working at Tandberg in Oslo, Norway.
Anders Mykkeltveit
Dependability differentiation in communication networks
2008-12-12
Unintentional failures affect links and nodes in communication networks. Recovery mechanisms are the key tool for achieving the dependability required by the services using the network. However, high dependability in communication networks comes at a high cost in terms of the capacity needed by these mechanisms. Since the users and services have different requirements, and users have different willingness to pay for a high quality of service, it is desirable to have methods that enable provision of different levels of dependability in the same network, i.e. dependability differentiation. The thesis addresses dependability differentiation in connection-oriented backbone communication networks.
Dr. Anders Mykkeltveit is now working at Telenor Global Services in Oslo, Norway.
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Stian Johansen
Rate-distortion optimization for video Communication in resource constrained IP networks
2008-03-03
Resource limitations lead to a number of challenges in all communication systems. This is also the case for video communication over networks based on the Internet Protocol (IP), where limited rates are shared among competing, heterogeneous users. Packet losses, delays and connectivity losses will be experienced to a varying degree depending on network loads, physical properties and mobility- related issues. These factors, as well as source coding characteristics, influence the visual quality experienced by the users. One of the main contributions of the work is that performance gains can be attained when considering characteristics of source coding, networks and congestion control jointly. Throughout the presented work, optimization of visual quality is at the centre of attention.
Dr. Stian Johansen is now working at Tandberg in Oslo, Norway.
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Karin Sallhammar
Stochastic models for combined security and dependability evaluation
2007-08-17
To be considered trustworthy, a system must be both dependable and secure. However, these two aspects have so far tended to be treated separately. A unified modelling framework for security and dependability evaluation would be advantageous from both points of view. The security community can benefit from the mature dependability modelling techniques, which can provide the operational measures that are so desirable today. On the other hand, by adding hostile actions to the set of possible fault sources, the dependability community will be able to make more realistic models than the ones that are currently in use. The thesis proposes a stochastic modelling approach, which can be used to predict a system's security and dependability behavior.
Dr. Karin Sallhammar is now working at Telenor Research and Innovation (R&I) in Trondheim, Norway.
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Odd Inge Hillestad
Evaluating and enhancing the performance of IP-based streaming media services and applications
2007-06-08
O. I. Hillestads PhD thesis deals with multimedia communication over unreliable and resource-constrained IP-based packet-switched networks. The focus is on estimating, evaluating and enhancing the quality of streaming media services, and streaming video services in particular.
Dr. Odd Inge Hillestad is now working at T-VIPS.
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Andre Årnes
Risk, privacy, and security in computer networks
2006-12-15
A. Årnes' PhD thesis entitled “Risk, Privacy, and Security in Computer Networks” introduces a novel approach to real-time network risk assessment based on hidden Markov models to represent the likelihood of transitions between security states. Further, measures for anonymization and pseudonymization are analyzed with respect to the trade-off of performing meaningful data analysis while protecting the identities of the users, and a novel method for performing digital forensic reconstructions in a virtual security testbed is proposed.
From the 1. of January 2007, Dr. Andre Årnes is back working for Politiets Datakrimsenter at Nye Kripos in Oslo, Norway.
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More information (in Norwegian)
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