FBE- Bilgisayar Mühendisliği Lisansüstü Programı - Yüksek Lisans

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  • Öge
    Wireless access management design in software defined networks
    (Institute of Science and Technology, 2016-06-03) Ariman, Mehmet ; Canberk, Berk ; 504111551 ; Computer Engineering
    ISP based Wi-Fi Hotspot deployments have emerged potential for offloading cellular traffic through existing hotspot deployments, increasing indoor coverage and providing continuous service access to the end users. ISPs favors the utilization of existing Wi-Fi infrastructure for offloading the cellular traffic. Furthermore, growth in the number of hotspots continues as a result of ISPs investments on Wi-Fi based hotspots. Cisco VNI report also revealed the potential of Wi-Fi Hotspot deployment for service providers by estimating the number of Wi-Fi devices as three-fold of cellular devices by 2020. In addition, ISPs such as Turkish Telecom expands the Wi-Fi Hotspot coverage by offering contracted customers a free Wi-Fi access in public Wi-Fi access areas in exchange of using customer's equipment for broadcasting ISPs SSID and customer's line for carrying the traffic. Indoor coverage area of ISPs also increased with given marketing strategy. Furthermore, the customers benefit from the free access of carrier's Wi-Fi hotspots and reached a continuous service access in public places as well. However, management of radio resources such as channel assignments of hotspots, wireless user access control, flow admission control of the users and new service deployment are the main issues which need to be addressed by the ISPs. Lead access point vendors such as Cisco, Aruba and Ruckus Wireless which holds more than 50% of the market share in top five access point vendors offer vendor-specific solutions for the issues given above. However, architecture and protocol overlay of the Wi-Fi Access Network solution varies for different vendors. Thus, inter-operability of vendor-specific solutions are limited. To this end, service deployment process becomes unnecessarily complex for ISPs when vendor-specific solutions are applied to the field. Additionally, requirement for standardization is highlighted by ISPs and effort has been put by technology pioneers such as Cisco. As a result, CAPWAP [6] is developed and deployed as a solution candidate. What's more, CAPWAP [6] recently became the most common management protocol used for wireless access networks. As a result of bottleneck in traffic relayed to the wireless controller in CAPWAP [6] and requirement for vendor-specific implementation for resource utilization, research in ISP based Wi-Fi access management on vendor-agnostic solutions and resolving the bottleneck problem in controller still needs to be addressed. SDN separates the control logic and the forwarding logic of the network into two separate domains: control plane and data plane. A controller is employed in control plane for running the logical operations of the network such as forwarding logic, access control and firewall etc. The controller installs the forwarding and blocking rules into the flow tables of the access elements placed in the data plane of the SDN topology. The controller installs the rules to the flow tables using a protocol which is standardized by ONF and named as OpenFlow. The access elements placed in the data plane are generic devices designed to run forwarding logic installed in their flow tables by the controller and named as OpenFlow Switches. SDN approach enables the optimization of radio resources and load balancing in the access network using the global view of the controller. The highlighted features of the SDN enhanced together makes SDN a promising candidate for addressing the unresolved problems, vendor-specific nature of existing solutions and bottleneck in traffic relayed to the controller, in management of ISP based wireless access network. To this end, a new wireless access management protocol, SDN-WAM, has been designed within the context of this thesis. SDN-WAM virtualizes each wireless client as an interface of the generic access device. In addition, the access control of wireless users are mapped to the open and shutdown events of interfaces. Traffic monitoring interface module is developed to track the bandwidth consumption of each flow generated by the users. The flow admission is handled by the basic flow admission control algorithm module which utilizes information gathered by the traffic monitoring interface. Finally, the access control of wireless clients are handled by designed access control module, which aims to balance the load of access devices. Additionally, an SDWN testbed has been developed within the context of this thesis to prove the validity of the offered wireless access management protocol. Opendaylight is used as the controller of the SDWN network. Traffic Monitoring Interface Module, Flow Admission Control Algorithm Module and Access Control Module defined in SDN-WAM is implemented as a north-bound module to the Opendaylight. The hardware of OF switches implemented in the testbed consists of Raspberry Pi with Pi-Hut USB Wi-Fi dongle. The wireless driver of OF switches is modified to provide the virtualization function described in SDN-WAM. This thesis is finalized by presenting the monitoring results, which prove the applicability of the given protocol to real-life deployment scenarios.
  • Öge
    DCfRSM: Fault-Tolerant checkpoint approach for replicated state machines
    (Institute of Science and Technology, 2020) Çelikel, Niyazi Özdinç ; Ovatman, Tolga ; 637414 ; Department of Computer Engineering
    As a result of attractive offers including serverless hosting services by cloud vendors, usage of state machine models has been widely spread in various areas in terms of software development for cloud. Serverless computing phenomenon offers software developers not only eliminating the need to take care of many aspects of software development stack but also focusing on developing main tasks to be executed by cloud system. Using state machine models in order to express the required functionality in one of the popular approaches for serverless computing. Cloud vendors also offers non functional requirements such as fault tolerance, integrability, etc. Replicating a single state machine across cluster which is going to work in distributed manner with the aim of handling requests is very well-known approach for providing fault tolerance. With other words, a major approach that can be used in fault tolerance is checkpointing. Checkpointing offers saving the system state in specific frequencies in order to boot the system back in case of any failure. Especially, applying different checkpointing approaches in replicated state machine systems is an highly active research topic for today's cloud computing era. In this thesis, advantages of splitting snapshots of replicated state machine images with the aim of decreasing memory overhead during persisting the system context is investigated.
  • Öge
    Step length estimation using sensor fusion for indoor positioning
    (Institute of Science and Technology, 2020) Sevinç, Hasbi ; İnce, Gökhan ; 637456 ; Department of Computer Engineering
    People use navigation applications to go to one place from another. Especially, if people traveling go to a place for the first time or if there is not enough information about the place, people traveling can get help from navigation applications. Navigation applications detect the person's location from Global Positioning System (GPS) or base station signals. However, the quality of these signals is not sufficient to use navigation applications in closed areas. In closed areas such as shopping centers, map information is usually provided through kiosk devices. The person looking for a store finds the store using the signs on the map at the mall. However, this is not possible for visually impaired people. Visually impaired individuals can reach their destination in open areas with navigation applications that use voice guidance. However, it is not possible to use these applications indoors, since they do not work properly in these locations. This study aims to provide navigation in indoor locations by using wearable and mobile devices. Various studies have been carried out to provide navigation in indoor locations. These studies generally used wireless networks such as WiFi, Bluetooth, Radio Frequency Identification (RFID). The basic principle of these systems is the calculation of the distance to the network devices that emit signals. If the distance to three or more devices is known, the position of the person can be obtained. However, in these studies, some technical arrangements should be made in the building for the system to function properly. Therefore, indoor areas where navigation is provided with the help of signals are not widely available. In robotic studies, different methods have been developed for indoor location tracking. In these studies, robots generally find their positions according to predefined objects or Quick Response (QR) codes in the field. However, the robot needs to know the position of the objects in the environment to find its position. In the method presented in this thesis, it is aimed that there is no need for any installation inside the building to follow the position of the person. For the study of the method presented in the thesis, the following elements were used: 1) textile-based capacitive sensors, 2) smart mobile phone, 3) WeWALK smart cane developed for the visually impaired. The data collection that is required for training of machine learning models were carried out with five different subjects walking on the established course. This track consists of walking paths with different stride lengths. Data taken from the sensors while the subjects walked in these areas were recorded by the system for further processing. Textile-based capacitive sensors are placed in both knees of the subject. These sensors measure the angle changes in the subject's knee joint. Thus, the system obtains information about the steps that the subject takes while walking. Information about the characteristics of walking is obtained by using the accelerometer, gyroscope, and the compass sensor in the smart cane and mobile phone. The direction of the walking subject was obtained from the compass sensor inside the mobile phone. As the first stage of the study, the data on the sensors were transmitted via Bluetooth connection. The system includes acceleration, gyroscope, and compass signals on x, y, and z axes for each of the smart canes and mobile phones. It also collects signals from the textile-based capacitive sensor. In total, the system collects nineteen signals. Firstly, the data collected from the sensors are cleaned from noise and outlier data using signal processing methods. An algorithm has been developed to detect the onset and offset points of the steps in the signal received from textile-based capacitive sensors. This algorithm calculates the local maximum and minimum points in the sensor signal and treats the interval between these points as steps. The signals in all sensors are segmented according to the determined start and finish points. In order to use sensor signals in regression models, feature extraction is performed on these signals. To improve the performance of the system, the extracted features are simplified by different feature selection methods. The performance of different methods were compared and regression models were trained with the best selection method. The system was trained with 1) Linear Regression, 2) Vector Support Regression, 3) Random Forest, 4) k-Nearest Neighbor models to find the best-fitted regression for the collected data set. The results obtained with these trained models were compared and the model with the best results was used for step detection. Sensor fusion was used to better determine stride lengths. In order to determine the contributions of the three different sensors in the system, different fusion alternatives have been tested separately and in pairs. As a result of these tests, it was observed that the fusion of three different sensors together provided the highest accuracy for step detection and lowest localization error. An Android application using Google Maps has been developed to perform localization. First of all, the plan prepared with the actual dimensions of the test environment was loaded on the map of the application. The initial location of the person in the test environment is defined in the application and this location is shown on the map with a marker. The application uses the regression models developed to determine the step length. Sensor data collected via Bluetooth is subjected to the same signal processing methods as in the learning phase of the model. Thus, when the person starts walking, the application determines the step length of the person with the help of the model and it updates the marker on the map according to the person's direction information. In order to test the system performance, a track with the same origin and destination points was determined in the test environment. When the person completed the entire track starting from the initial point, the distance between their actual final position and the projected final position was calculated. The method developed in this thesis aims to enable the visually impaired to reach their desired destinations in indoor locations by using the smart cane, textile-based capacitive sensor, and smartphones. With the data collected in walking tests, the development of regression models, and the Android application showing the position on the map, this study contributes to literature in the indoor localization and navigation.
  • Öge
    An enhanced two phase commit protocol for high performance consistency management in replicated state machines
    (Institute of Science and Technology, 2020-07) Uyanık, Halit ; Ovatman, Tolga ; 637248 ; Computer Engineering Department
    State Machines are used to represent a set of transitions, which makes it a useful tool for representing life-cycle of a specific set of events. By utilizing this property, a state machine can be replicated into several machines and each one of them can communicate with one another in order to keep track of the order of changes. This is called the replicated state machine approach and it is highly used in replicated data services where there is a need to manage the consistency of a system. In order to provide any consistency, it is necessary to use a communication algorithm which provides both high throughput, and less number of failures in the case of conflicting operations. One of the widely known communication protocols used in our context is the two-phase commit (2PC) protocol. It provides a two step algorithm in order to manage the committing actions between different machines for the same resource. First it checks if every machine in a network is ready for writing operation, then if a machine receives a successful message from all other machines, it will then proceed to commit the specific operation to all of them. Finally it applies the commit to its own resource. In the case of no priority between the writing actions between different machines, algorithm gives the commit rights to the first machine which can successfully receive OK from all others. However, when priority comes into action, and it becomes necessary to cancel out transitions with less importance, algorithm starts to cancel out some incoming transitions, and in most cases, if the writing operations are too frequent, it cancels out a writing operation even if it obtains its OK from other machines. Disadvantage of the common 2PC algorithm in the case of priority introduction, due to its phases follow one another without any transitions, when an incoming writing request fails, it has to repeat all the preceding events from that point again. When the distance between the last important point of no-return, such as reading a value into cache, and the point of 2PC protocol becomes further away, this affect is increased and the number of messages for a successful transition is increased. In order to reduce the overhead introduced by this problem, a new algorithm is implemented by enhancing the existing 2PC algorithm. Both steps of the 2PC algorithm mentioned is separated from one another, and can be freely deployed in any place on a state machine, as long as their order is preserved.
  • Öge
    Etmen tabanlı otomatik müzayede ortamının tasarım ve gerçeklenmesi
    (Fen Bilimleri Enstitüsü, 2020) Güleryüz, Uğur ; Erdoğan, Takuhi Nadia ; 636880 ; Bigisayar Mühendisliği
    Teknolojinin gelişmesi ile beraber internetin yaygınlaşmasından önce reel olarak yapılan pek çok işlem sanal ortama taşınmış ve daha az efor harcayarak yapılabilir hale gelmiştir. Günümüzde alışverişler büyük oranda online olarak yapılmaya başlanmıştır, satıcılar ürünlerini farklı yöntemler kullanarak satabilmektedir. Müzayedeler ürün satışı yapmak için kullanılan yaygın yöntemlerden birisidir ve günümüzde pek çok ürün farklı müzayede yöntemleri ile internet üzerinden satılabilmektedir. Farklı müzayede yöntemleri ile ürün satışı yapılırken hem alıcı hem de satıcı tarafının müzayedenin her aşamasını dikkatle takip etmesi ve ürünü satın alma isteği ve bütçesine göre doğru stratejilerle hareket etmesi son derece önemlidir. Fakat müzayedeyi takip etmek için yeterli zamanı olmayan veya aynı anda birden fazla müzayedeye alıcı veya satıcı olarak katılmış katılımcılar için müzayedeyi takip etme işlemi oldukça zor hale gelmektedir. Bu sebeple kullanıcının önceden belirlediği parametrelerle hem alıcı hem de satıcı tarafında müzayede takibini kullanıcı yerine otomatik yapacak bir sisteme ihtiyaç duyulmaktadır. Bu çalışmada kullanıcıların farklı tip müzayede yöntemleri kullanarak ürün alma ve ürün satma işlemlerini isterse manual isterse önceden gireceği parametre ve stratejilere göre otomatik olarak yapabileceği bir ortam tasarlanmış ve gerçeklenmiştir. Bu ortam tamamen etmen tabanlı olarak gerçeklenmiş ve uygulamanın ana bileşenleri etmenlerle ifade edilmiştir. Server, arayüz, teklif, müzayede olmak üzere dört tip etmen bulunmakta ve her etmen kendi temsil ettiği bileşenle alakalı işleri gerçekleştirmektedir. Farklı etmen tipleri kendi aralarında haberleşerek sistemin ana akışını oluşturmaktadır. Sistem İngiliz ve Hollandalı tipi müzayedeleri desteklemektedir ve her müzayede tipi için alıcı ve satıcı tarafına farklı stratejiler sunmaktadır. Hollandalı tipi müzayedede ücret değişimlerini yapan satıcı tarafına farklı ücret düşürme stratejileri sunmaktadır. Alıcı tarafına ise otomatik olarak müzayedeyi takip ederek istediği ücrete düştüğünde ürünü satın alma seçeneği sunmaktadır. İngiliz tipi müzayedede ise satıcı tarafına istediği ücrete ulaştığında otomatik olarak ürünü satma seçeneği sunmadktadır. Alıcı tarafına ise ister otomatik olarak belirlediği stratejide periyodik olarak teklifler verme ister belirlediği zamanda belirlediği miktarda teklif yapma seçeneği sunmaktadır. Yapılan deneylerde sistemin sunduğu seçeneklerle iki tip müzayede tipi içinde kullanıcının isteklerini karşıladığı, alıcıların ve satıcıların bütçeleri, ürünü alma veya satma isteklerine göre belirlediği stratejiler ve girdiği parametrelerle müzayedelere katılım sağlayabildiği gözlemlenmiştir. Sunulan stratejiler karşılaştırılmış olup farklı durumlarda farklı stratejilerin öne çıktığı ve müzayedenin sonucuna büyük oranda etki ettiği gözlemlenmiştir.