Browsing by department "Department of Computer Science"

The purpose of this thesis was to analyze the testing requirements to physical layer features which are used in LTE Release 9 and 10 timeframe. The aim of the analysis was to define test case requirements for new features from the physical layer point of view. This analysis can then be utilized to implement and design test cases using commercial eNB simulators. The analysis was carried out by studying the 3GPP specifications and by investigating the integration and system level testing requirements. Different feature specific parameters were evaluated and different testing aspects were studied in order to verify the functionalities and performance of the UE. Also, different conformance test case scenarios and field testing aspects were investigated in order to improve the test case planning in the integration and system testing phase. The analysis showed that in Rel-9 there are two main features which have a great impact on the Rel-9 physical layer testing. These two features are the dual-layer beamforming and UE positioning which is done with OTDOA and E-CID methods. It was analyzed that the requirements for the downlink dual-layer beamforming focus on TDD side and the test plan must contain especially throughput performance testing in integration and system phase testing. OTDOA and E-CID methods, on the other hand, need test plans which are concentrating on the positioning accuracy. In Rel-10, the analysis showed that there are plenty of new features on physical layer to ensure the transition from LTE to LTE-Advanced. The main requirements were assigned for the CA feature which has testing activities especially on the UE feedback operations. Also, different kinds of CA deployment scenarios were analyzed to evaluate more closely the initial CA testing scenarios in integration and system testing. Analysis continued with downlink multi-layer beamforming where the requirements were seen to concentrate on new CSI-RS aspects and to throughput performance testing. Uplink MIMO aspects were analyzed at the end and the studies showed that this feature may have a minor role in Rel-10 timeframe and therefore it does not have any important testing requirements which should be taken into account in test plans.

De-anonymization is an important requirement in real-world V2X systems (e.g., to enable effective law enforcement). In de-anonymization, a pseudonymous identity is linked to a long-term identity in a process known as pseudonym resolution. For de-anonymization to be acceptable from political, social and legislative points of view, it has to be accountable. A system is accountable if no action by it or using it can be taken without some entity being responsible for the action. Being responsible for an action means that the responsible entity cannot deny its responsibility of or relation to an action afterwards. The main research question is: How can we achieve accountable pseudonym resolution in V2X communication systems? One possible answer is to develop an accountable de-anonymization service, which is compatible with existing V2X pseudonym schemes. The accountability can be achieved by making some entities accountable for the de-anonymization. This thesis proposes a system design that enables, i) fine-grained pseudonym resolution; ii) the possibility to inform the subject of the resolution after a suitable time delay; and iii) the possibility for the public to audit the aggregate number of pseudonym resolutions. A TEE is used to ensure these accountability properties. The security properties of this design are verified using symbolic protocol analysis.

A Bayesian Network (BN) is a graphical model applying probability and Bayesian rule for its inference. BN consists of structure, that is a directed acyclic graph (DAG), and parameters. The structure can be obtained by learning from data. Finding an optimal BN structure is an NP-Hard problem. If an ordering is given, then the problem becomes simpler. Ordering means the order of variables (nodes) for building the structure. One of structure learning algorithms that uses variable ordering as the input is K2 algorithm. The ordering determines the quality of resulted network. In this work, we apply Cuckoo Search (CS) algorithm to find a good node ordering. Each node ordering is evaluated by K2 algorithm. Cuckoo Search is a nature-inspired metaheuristic algorithm that mimics the aggressive breeding behavior of Cuckoo birds with several simplifications. It has outperformed Genetic Algorithms and Particle Swarm Optimization algorithm in finding an optimal solution for continuous problems, e.g., functions of Michalewicz, Rosenbrock, Schwefel, Ackley, Rastrigin, and Griewank. We conducted experiments on 35 datasets to compare the performances of Cuckoo Search to GOBNILP that is a Bayesian network learning algorithm based on integer linear programming and it is well known to be used as benchmark. We compared the quality of obtained structures and the running times. In general, CS can find good networks although all the obtained networks are not the best. However, it sometimes finds only low-scoring networks, and the running times of CS are not always very fast. The results mostly show that GOBNILP is consistently faster and can find networks of better quality than CS. Based on the experiment results, we conclude that the approach is not able to guarantee obtaining an optimal Bayesian network structure. Other heuristic search algorithms are potentially better to be used for learning Bayesian network structures that we have not compared to our works, for example the ordering-search algorithm by Teyssier and Koller [41] that combines greedy local hill-climbing with random restarts, a tabu list, caching computations, and a heuristic pruning procedure.

Software delivery has evolved notably over the years, starting from plan-driven methodologies and lately moving to principles and practises shaped by Agile and Lean ideologies. The emphasis has moved from thoroughly documenting software requirements to a more people-oriented approach of building software in collaboration with users and experimenting with different approaches. Customers are directly integrated into the process. Users cannot always identify software needs before interacting with actual implementations. Building software is not only about building products in the right way, but also about building the right products. Developers need to experiment with different approaches, directly and indirectly. Not only do users value practical software, but the development process must also emphasise on the quality of the product or service. Development processes have formed to support these ideologies. To enable a short feedback-cycle, features are deployed often to production. A software is primarily delivered through a pipeline consisting of tree stages: development, staging and production. Developers develop features by writing code, verify these by writing related tests, interact and test software in a production-like 'staging' environment, and finally deploy features to production. Many practises have formed to support this deployment pipeline, notably Continuous Integration, Deployment and Experimentation. These practises focus on improving the flow of how software is being developed, tested, deployed and experimented with. The Internet has provided a thriving environment for using new practises. Due to the distributed nature of the web, features can be deployed without the need of any interaction from users. Users might not even notice the change. Obviously, there are other environments where many of these practises are much harder to achieve. Embedded systems, which have a dedicated function within a larger mechanical or electrical system, require hardware to accompany the software. Related processes and environments have their limitations. Hardware development can only be iterative to a certain degree. Producing hardware takes up front design and time. Experimentation is more expensive. Many stringent contexts require processes with assurances and transparency - usually provided by documentation and long-testing phases. In this thesis, I explore how advances in streamlining software delivery on the web has influenced the development of embedded systems. I conducted six interviews with people working on embedded systems, to get their view and incite discussion about the development of embedded systems. Though many concerns and obstacles are presented, the field is struggling with the same issues that Agile and Lean development are trying to resolve. Plan-driven approaches are still used, but distinct features of iterative development can be observed. On the leading edge, organisations are actively working on streamlining software and hardware delivery for embedded systems. Many of the advances are based on how Agile and Lean development are being used for user-focused software, particularly on the web.

A measurement for how similar (or distant) two computer programs are has a wide range of possible applications. For example, they can be applied to malware analysis or analysis of university students' programming exercises. However, as programs may be arbitrarily structured, capturing the similarity of two non-trivial programs is a complex task. By extracting call graphs (graphs of caller-callee relationships of the program's functions, where nodes denote functions and directed edges denote function calls) from the programs, the similarity measurement can be changed into a graph problem. Previously, static call graph distance measures have been largely based on graph matching techniques, e.g. graph edit distance or maximum common subgraph, which are known to be costly. We propose a call graph distance measure based on features that preserve some structural information from the call graph without explicitly matching user defined functions together. We define basic properties of the features, several ways to compute the feature values, and give a basic algorithm for generating the features. We evaluate our features using two small datasets: a dataset of malware variants, and a dataset of university students' programming exercises, focusing especially on the former. For our evaluation we use experiments in information retrieval and clustering. We compare our results for both datasets to a baseline, and additionally for the malware dataset to the results obtained with a graph edit distance approximation. In our preliminary results we show that even though the feature generation approach is simpler than the graph edit distance approximation, the generated features can perform on a similar level as the graph edit distance approximation. However, experiments on larger datasets are still required to verify the results.

The conferencing systems in IP Multimedia (IM) networks are going through restructuring, accomplished in the near future. One of the changes introduced is the concept of floors and floor control in its current form with matching entity roles. The Binary Floor Control Protocol (BFCP) is a novelty to be exploited in distributed tightly coupled conferencing services. The protocol defines the floor control server (FCS), which implements floor control giving access to shared resources. As the newest tendency is to distribute the conferencing services, the locations of different functionality units play an important role in developing the standards. The floor control server location is not yet single-mindedly fixed in different standardization bodies, and the debate goes on where to place it within the media server, providing the conferencing service. The thesis main objective is to evaluate two distinctive alternatives in respect the Mp interface protocol between the respective nodes, as the interface in relation to floor control is under standardization work at the moment. The thesis gives a straightforward preamble in IMS network, nodes of interest including floor control server and conferencing. Knowledge on several protocols – BFCP, SDP, SIP and H.248 provides an important background for understanding the functionality changes introduced in the Mp interface and therefore introductions on those protocols and how they are connected to the full picture is given. The actual analysis on the impact of the floor control server into the Mp reference point is concluded in relation to the locations, giving basic flows, requirements analysis including a limited implementation proposal on supporting protocol parameters. The overall conclusion of the thesis is that even if both choices are seemingly useful, not one of the locations is clearly the most suitable in the light of this work. The thesis suggests a solution having both possibilities available to be chosen from in separate circumstances, realized with consistent standardization. It is evident, that if the preliminary assumption for the analysis is kept regarding to only one right place for the floor control server, more work is to be done in connected areas to discover the one most appropriate location.

Expected benefits from agile methodologies to project success have encouraged organizations to extend agile approaches to areas they were not originally intended to such as large scale information systems projects. Research regarding agile methods in large scale software development projects have existed for few years and it is considered as its own research area. This study investigates agile methods on the large scale software development and information systems projects and its goal is to produce more understanding of agile methods suitability and the conditions under which they would most likely contribute to project success. The goal is specified with three research questions; I) what are the characteristics specific to large scale software engineering projects or large scale Information Systems project, II) what are the challenges caused by these characteristics and III) how agile methodologies mitigate these challenges? In this study resent research papers related to the subject are investigated and characteristics of large scale projects and challenges associated to them are recognized. Material of the topic was searched starting from the conference publications and distributions sites related to the subject. Collected information is supplemented with the analysis of project characteristics against SWEBOK knowledge areas. Resulting challenge categories are mapped against agile practises promoted by Agile Alliance to conclude the impact of practises to the challenges. Study is not a systematics literature review. As a result 6 characteristics specific to large scale software development and IS projects and 10 challenge categories associated to these characteristics are recognized. The analysis reveals that agile practises enhance the team level performance and provide direct practises to manage challenges associated to high amount of changes and unpredictability of software process both characteristic to a large scale IS project but challenges still remain on the cross team and overall project level. As a conclusion it is stated that when seeking the process model with agile approach which would respond to all the characteristics of large scale project thus adding the likelihood of project success adaptations of current practises and development of additional practises are needed. To contribute this four areas for adaptations and additional practises are suggested when scaling agile methodologies over large scale project contexts; 1) adaptation of practises related to distribution, assignment and follow up of tasks, 2) alignment of practises related to software development process, ways of working and common principles over all teams, 3) developing additional practises to facilitate collaboration between teams, to ensure interactions with the cross functional project dimensions and to strengthen the dependency management and decision making between all project dimensions and 4) possibly developing and aligning practises to facilitate teams' external communication. Results of the study are expected to be useful for software development and IS project practitioners when considering agile method adoptions or adaptations in a large scale project context. ACM Computing Classification System (CCS) 2012: - Social and professional topics~Management of computing and information systems - Software and its engineering~Software creation and management

Tutkielmassa arvioidaan aktoripohjaisten rinnakkaistamisratkaisujen soveltuvuutta pelimoottoreihin. Tutkielmassa esitellään ensin pelimoottoreiden ja aktoripohjaisen rinnakkaisuuden perusperiaatteet ja sitten aktoripohjainen Stage-pelimoottoritoteutus. Tutkielman lopuksi tutkitaan Stage-moottorin tehokkuutta ja helppokäyttöisyyttä verrattuna perinteisiä lukkopohjaisia rinnakkaistamisratkaisuja hyödyntävään pelimoottoriin.

The number of applications that are used for voice and video calls is growing day by day. The basic purpose of all of these applications is to provide better call services to their customers. These applications differ in their underlying communication protocols and encoding techniques. These variations in protocols are introduced to enhance the user experience, improve the performance of the VoIP applications and minimize the network delay between the end users. Thus, to make the call quality better, there is a lot of research done to analyze and detect VoIP traffic. There are two basic goals of this thesis: 1) Analysis of the VoIP traffic of five famous VoIP applications (Skype, Viber, WhatsApp, Facebook messenger, and IMO). 2) Classification of VoIP traffic based on the analysis in the first step. We adopted flow-based analysis technique for the analysis and classification of VoIP traffic. For the first step, we analyzed the three flow features (packet rate, Inter-packet gap, and packet size) of the above-chosen VoIP applications. In addition, we also presented a detailed explanation of the three factors (the access network, the underlying operating system, and the geographic distance between the caller and the callee) which can affect distribution of the flows features. To realize our second goal, we present an analysis algorithm that uses moving weighted average (EWMA) and standard deviation (EWMSD). Our analysis algorithm is based on the statistical distribution of EWMA/EWMSD for each of the selected flow features mentioned above. The advantage of using EWMA/EWMSD statistics for classification is that they are not dependent on network protocols. Thus, a generic classification approach can be applied to all of the three flow features described above. Finally, based on our analysis, we introduce a classifier algorithm and its variants to classify a VoIP call as voice or video call. The classifier algorithm monitors EWMA/EWMSD statistics for the flow features and classifies the content of VoIP call accordingly. Our results explain two important things: 1) Each of the above-mentioned flow features can be used with EWMA/EWMSD statistics for VoIP traffic classification. 2) The use of Inter- packet gap feature with EWMA/EWMSD statistics gives highly accurate results as compared to the Packet size and Packet rate.