The thesis contains a complete theoretical overview of high availability technologies in Microsoft SQL Server. For each technology, guidance is provided for the deployment of technologies. Technologies are analyzed from a security perspective, they are determined advantages and disadvantages of using technology in practice and is determined the optimal variant of use of the technology. High availability technology are compared with each other and is given the availability of individual technologies in versions of MS SQL Server. The thesis contains three scenarios with practical examples of using technology for high availability in practice. It provides an analysis of high-availability features in Oracle and are subsequently compared high availability features in Oracle environments with high availability technology in MS SQL Server.

In recent years, Internet and IP technologies have made inroads into almost every communication market ranging from best-effort services such as email and Web, to soft real-time applications such as VoIP, IPTV, and video. However, providing a transport service over IP that meets the timeliness and availability requirements of soft real-time applications has turned out to be a complex task. Although network solutions such as IntServ, DiffServ, MPLS, and VRRP have been suggested, these solutions many times fail to provide a transport service for soft real-time applications end to end. Additionally, they have so far only been modestly deployed. In light of this, this thesis considers transport protocols for soft real-time applications. Part I of the thesis focuses on the design and analysis of transport protocols for soft real-time multimedia applications with lax deadlines such as image-intensive Web applications. Many of these applications do not need a completely reliable transport service, and to this end Part I studies so-called partially reliable transport protocols, i.e., transport protocols that enable applications to explicitly trade reliability for improved timeliness. Specifically, Part I investigates the feasibility of designing retransmission-based, partially reliable transport protocols that are congestion aware and fair to competing traffic. Two transport protocols are presented in Part I, PRTP and PRTP-ECN, which are both extensions to TCP for partial reliability. Simulations and theoretical analysis suggest that these transport protocols could give a substantial improvement in throughput and jitter as compared to TCP. Additionally, the simulations indicate that PRTP-ECN is TCP friendly and fair against competing congestion-aware traffic such as TCP flows. Part I also presents a taxonomy for retransmission-based, partially reliable transport protocols. Part II of the thesis considers the Stream Control Transmission Protocol (SCTP), which was developed by the IETF to transfer telephony signaling traffic over IP. The main focus of Part II is on evaluating the SCTP failover mechanism. Through extensive experiments, it is suggested that in order to meet the availability requirements of telephony signaling, SCTP has to be configured much more aggressively than is currently recommended by IETF. Furthermore, ways to improve the transport service provided by SCTP, especially with regards to the failover mechanism, are suggested. Part II also studies the effects of Head-of-Line Blocking (HoLB) on SCTP transmission delays. HoLB occurs when packets in one flow block packets in another, independent, flow. The study suggests that the short-term effects of HoLB could be substantial, but that the long-term effects are marginal.

Orientador : Prof. Dr. Nunzio Marco Torrisi / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Ciência da Computação, 2016. / As redes de computadores estão sofrendo mudanças ao longo dos últimos anos e várias tecnologias vem sendo implementadas com o intuito de renovar a forma de comunicação entre os dispositivos, quer sejam mudanças em meio físico (como aumento largura de banda devido a tecnologia de fibra ótica e novas tecnologias de comunicação wireless), quer sejam mudanças no modo de comunicação (diminuição do overhead de cabeçalhos, novos protocolos de comunicação(HTTP2), utilização de software para definir comportamento de rede. Um dos poucos pontos em que essas mudanças tecnológicas não interferiram foi no modo com o qual os dispositivos recebem seu endereço de rede, que ainda é através de um servidor DHCP. Dado este fato e a evolução do modelo tradicional de rede para redes definidas por software, este trabalho foi desenvolvido utilizando as funções presentes tanto no protocolo DHCP quanto nas Redes Definidas por Software criando uma solução de redundância múltipla do serviço de DHCP. / Computer networks are changing over the last few years, many technologies are being implemented as a way to renew how hosts should communicate between themselves. Some physical changes: increase of bandwidth through fiber optics technology, new wireless protocol; some software changes: decreasing protocol header overhead, new communication protocols(HTTP2), use of software to define network behavior. On the other hand, the way of network devices gets their IP address inside a network is one of the few features that those technology changes did not interfere, devices¿ IP addresses are still delivered by a DHCP server. Through these facts and the evolution of traditional computer networks to software defined networks, this work was developed merging some software defined network functions with DHCP functions in order to raise a new multiple redundancy DHCP service solution.

The master‘s thesis deals with the implementation of server virtualization in the Entity production, s.r.o., which is a small company by it’s size, but needs modern IT technologies for the normal operations. The thesis shows how to reuse the server virtualization technologies from large corporations, that have been unavailable to small business companies in past. It also design show to optimize the current IT environment.

One of the main challenges in the Multi-access Edge Computing (MEC) issteering traffic from clients to the nearest MEC instances. If the nearest MECfails, a failover mechanism should provide mitigation by steering the trafficto the next nearest MEC. There are two conventional approaches to solve thisproblem, i.e., GeoDNS and Internet Protocol (IP) anycast. GeoDNS is notfailover friendly because of the Domain Name System (DNS) cache lifetime.Moreover, the use of a recursive resolver may inaccurately translate the IPaddress to its geolocation. Thus, this thesis studies and proposes a highlyavailable MEC platform leveraging IP anycast. We built a proof-of-conceptusing Kubernetes, MetalLB, and a custom health-checker running on theGNS3 network emulator. We measured latency, failure percentage, and MeanTime To Repair (MTTR) to observe the system’s behavior. The performanceevaluation of the proposed solution shows an average recovery time betterthan one second. The number of failed requests and latency overhead growslinearly as the failover time and latency between two MECs increases. Thisthesis demonstrates the effectiveness of IP anycast for MEC applications tosteer the traffic to the nearest MEC instance and to enhance resiliency withminor overhead. / n av de största utmaningarna i Multi-access Edge Computing (MEC) är attstyra trafiken från klienter till närmaste MEC instanser. Om den närmasteMEC misslyckas, bör en failover-mekanism ge begränsning genom att styratrafiken till nästa närmaste MEC. Det finns två konventionella metoder för attlösa detta problem, dvs GeoDNS och IP anycast. GeoDNS är inte failovervänligtpå grund av DNS-cache-livslängd. Dessutom kan användningen aven rekursiv upplösare felaktigt översätta IP-adressen till dess geolokalisering.Således studerar och föreslår denna avhandling en mycket tillgänglig MEC-plattform som utnyttjar IP anycast. Vi byggde ett proof-of-concept medKubernetes, MetalLB och en anpassad hälsokontroll som körs på GNS3-nätverksemulatorn. Vi mätte latens, felprocent och Mean Time To Repair(MTTR) för att observera systemets beteende. Prestationsutvärderingen avden föreslagna lösningen visar en genomsnittlig återhämtningstid som ärbättre än en sekund. Antalet misslyckade förfrågningar och latensomkostnaderväxer linjärt när failover-tiden och latensen mellan två MEC ökar. Den häravhandlingen visar effektiviteten hos IP anycast för MEC-applikationer för attstyra trafiken till närmaste MEC instans och för att förbättra elasticiteten medmindre overhead.

This thesis is focused on the optimization of distributed IP flow information collector. Nowadays, the centralized collector is a frequently used solution but is already reaching its performance limits in large scale and high-speed networks. The implementation of the distributed collector is in its early phase and it is necessary to look for solutions that will use it to its full potential. Therefore this thesis proposes a shared nothing architecture without a single point of failure. Using the above proposed architecture, the distributed collector is tolerant to the failure of at least one node. A distributed flow data analysis software, whose performance scales linearly with the number of nodes, is also part of this thesis.

The goal of this master thesis is to analyze Open Source resources for loadbalancing and high availability, with aim on areas of its typical usage. These areas are particularly solutions of network infrastructure (routers, loadbalancers), generally network and internet services and parallel filesystems. Next part of this thesis is analysis of design, implementation and plans of subsequent advancement of an fast growing Internet project. The effect of this growth is necessity of solving scalability on all levels. The last part is performance analysis of individual loadbalancing methods in the Linux Virtual Server project.

This thesis deals with a load testing of web applications. The text is introduced with a definition of the load testing, reasons for its execution and a description of its types. Recommended procedures are provided for preparation, execution and evaluation of the testing. Several commercial and open-source load testing tools are described. Cloud testing -- the contemporary phenomenon -- is also included. The entire process of load testing depicted in this text is demonstrated on a selected application. A following chapter briefly deals with a profiling of web applications. It, again, covers its definition and its purpose, accompanied with a practical example. The aim of this thesis is to introduce the reader to the world of load testing, which is primarily accomplished by describing an example, which provides an in-depth explanation for every step necessary in order to perform the web application testing successfully.