Issues in designing transport layer multicast facilities

Multicasting denotes a facility in a communications system for providing efficient delivery from a message's source to some well-defined set of locations using a single logical address. While modem network hardware supports multidestination delivery, first generation Transport Layer protocols (e.g., the DoD Transmission Control Protocol (TCP) (15) and ISO TP-4 (41)) did not anticipate the changes over the past decade in underlying network hardware, transmission speeds, and communication patterns that have enabled and driven the interest in reliable multicast. Much recent research has focused on integrating the underlying hardware multicast capability with the reliable services of Transport Layer protocols. Here, we explore the communication issues surrounding the design of such a reliable multicast mechanism. Approaches and solutions from the literature are discussed, and four experimental Transport Layer protocols that incorporate reliable multicast are examined

Omejevanje dostopa pri obvladovanju API-jev

With ever growing usage of World Wide Web, number of requests to web APIs is increasing rapidly. DoS attacks and service abuses are becoming easier to execute, and more common every day. Quality of service is becoming more important as competition is rising. To build robust and reliable services, software engineers have to take this into account when designing web APIs, to deliver end users with a pleasant and reliable experience. In this thesis we delve into rate limiting in web API management to deal with those problems on scale. We propose an approach to rate limiting when request weighting is key, and cannot be estimated/calculated upfront. We show how integration of such approach into a real working system can help in achieving high stability and performance improvements, while unlocking some advanced API monetisation opportunities.Strma rast uporabe svetovnega spleta je silovito povečala število spletnih zahtevkov, ki jih morajo procesirati zaledni sistemi. Napadi za zavrnitev storitev in zlorabe le-teh so vse bolj pogosti in enostavni za izvedbo. Kvaliteta in zanesljivost sistemov sta ključnega pomena za ohranjanje konkurenčnosti. Naloga razvijalcev programske opreme je, da z upoštevanjem teh zahtev načrtujejo robustne sisteme, ki bodo uporabnikom omogočili prijetno in zane-sljivo uporabniško izkušnjo. V tej diplomski nalogi raziščemo pristop omejevanja dostopa pri obvladovanju API-jev za reševanje omenjenih problemov. Predlagamo pristop pri katerem je obteževanje spletnih zahtevkov ključnega pomena in ne more biti ocenjeno/izračunano pred procesiranjem zahtevka. Pokažemo kako lahko integracija takšnega pristopa v delujoč sistem občutno izboljša stabilnost in učinkovitost storitev ter odpre možnosti za nove načine trženja API-jev

Teleoperation of passivity-based model reference robust control over the internet

This dissertation offers a survey of a known theoretical approach and novel experimental results in establishing a live communication medium through the internet to host a virtual communication environment for use in Passivity-Based Model Reference Robust Control systems with delays. The controller which is used as a carrier to support a robust communication between input-to-state stability is designed as a control strategy that passively compensates for position errors that arise during contact tasks and strives to achieve delay-independent stability for controlling of aircrafts or other mobile objects. Furthermore the controller is used for nonlinear systems, coordination of multiple agents, bilateral teleoperation, and collision avoidance thus maintaining a communication link with an upper bound of constant delay is crucial for robustness and stability of the overall system. For utilizing such framework an elucidation can be formulated by preparing site survey for analyzing not only the geographical distances separating the nodes in which the teleoperation will occur but also the communication parameters that define the virtual topography that the data will travel through. This survey will first define the feasibility of the overall operation since the teleoperation will be used to sustain a delay based controller over the internet thus obtaining a hypothetical upper bound for the delay via site survey is crucial not only for the communication system but also the delay is required for the design of the passivity-based model reference robust control. Following delay calculation and measurement via site survey, bandwidth tests for unidirectional and bidirectional communication is inspected to ensure that the speed is viable to maintain a real-time connection. Furthermore from obtaining the results it becomes crucial to measure the consistency of the delay throughout a sampled period to guarantee that the upper bound is not breached at any point within the communication to jeopardize the robustness of the controller. Following delay analysis a geographical and topological overview of the communication is also briefly examined via a trace-route to understand the underlying nodes and their contribution to the delay and round-trip consistency. To accommodate the communication channel for the controller the input and output data from both nodes need to be encapsulated within a transmission control protocol via a multithreaded design of a robust program within the C language. The program will construct a multithreaded client-server relationship in which the control data is transmitted. For added stability and higher level of security the channel is then encapsulated via an internet protocol security by utilizing a protocol suite for protecting the communication by authentication and encrypting each packet of the session using negotiation of cryptographic keys during each session

Issues in providing a reliable multicast facility

Issues involved in point-to-multipoint communication are presented and the literature for proposed solutions and approaches surveyed. Particular attention is focused on the ideas and implementations that align with the requirements of the environment of interest. The attributes of multicast receiver groups that might lead to useful classifications, what the functionality of a management scheme should be, and how the group management module can be implemented are examined. The services that multicasting facilities can offer are presented, followed by mechanisms within the communications protocol that implements these services. The metrics of interest when evaluating a reliable multicast facility are identified and applied to four transport layer protocols that incorporate reliable multicast

Rate limiting in API management

With ever growing usage of World Wide Web, number of requests to web APIs is increasing rapidly. DoS attacks and service abuses are becoming easier to execute, and more common every day. Quality of service is becoming more important as competition is rising. To build robust and reliable services, software engineers have to take this into account when designing web APIs, to deliver end users with a pleasant and reliable experience. In this thesis we delve into rate limiting in web API management to deal with those problems on scale. We propose an approach to rate limiting when request weighting is key, and cannot be estimated/calculated upfront. We show how integration of such approach into a real working system can help in achieving high stability and performance improvements, while unlocking some advanced API monetisation opportunities

SysML for embedded automotive systems: SysCARS methodology

International audienceThis paper gives an overview of the years of Valeo experience in deploying a Model Based System Engineering (MBSE) approach for mechatronic automotive embedded systems and products. The different stages are described initial studies, language and tool benchmarking up to the last returns of experience on industrial projects. Particular emphasis is put on describing the SysCARS methodology which gives, not only a precise mapping of System Engineering work items to SysML artefacts, but also the sequence of modeling activities to be performed. It is shown how the SySCARS methodology has been implemented as a SysML profile, based on a powerful "workflow driven" mechanism, which helps the user during the modeling process. Finally it is presented how interoperability is ensured with the tools already in place for requirements management and control design

Design, development and testing of SOEC-based Power-to-Gas systems for conversion and storage of RES into synthetic methane

International and national initiatives are promoting the worldwide transition of energy systems towards power production mixes increasingly based on Renewable Energy Sources (RES). The integration of large shares of RES into the actual electricity infrastructure is representing a challenge for the power grids due to the fluctuating characteristics of RES. The adoption of long-term, large-scale Electric Energy Storage (EES) is envisaged as the key-option for promoting the integration of RES in the electricity sector by overcoming the issue of temporal and spatial decoupling of electricity supply and demand. Among the several EES options, one of the most promising is the conversion of energy from the electrical into the chemical form through the synthesis of H2 and synthetic natural gas (SNG) in Power-to-Gas (P2G) systems based on the electrolysis of water (and also CO2) in Solid Oxide Cells (SOCs). The application of SOC technology in P2G solutions shows attractiveness for the high efficiency of high-temperature electrolysis and the flexibility of SOCs that can operate reversibly as electrolyzers or fuel cells (rSOC) and can directly perform the electrochemical conversion of CO2 and H2O to syngas by co-electrolysis. The capability of reversible operation also allows the application of SOC-based systems to Power-to-Power (P2P) concepts designed for deferred electricity production. This dissertation is focused on the investigation of electricity storage using Power-to-Gas/Power systems based on SOCs. The aim of this Thesis has been the investigation of the thermo-electrochemical behavior of SOCs integrated P2G/P2P systems, with the purpose to identify the system configuration and the operating conditions that ensure the most efficient electricity-to-SNG (P2G) or electricity-to-electricity (P2P) conversion within the thermal limits imposed by state-of-the art SOC materials. To this purpose, a detailed thermo-electrochemical model of an SOC has been developed at cell level, validated on experimental data, extended at stack level and coupled with models of the main P2G/P2P components for the system analysis. Model validation was performed through the characterization of planar commercial SOCs in the reversible operation as electrolyzers (SOEC) and fuel cells (SOFC) with H2/H2O and CO/CO2 fuel mixtures at different reactant fractions and temperatures. The physical consistency of electrode kinetic parameters evaluated from the model was verified with the support of literature studies. The investigation of SOC-based P2P and P2G solutions was performed using the models developed. Three different configurations were analyzed and simulated: 1) hydrogen-based P2P with rSOC, 2) SOEC-based electricity storage into hydrogen with subsequent SNG production by methanation with CO2 and 3) electricity storage by co-electrolysis of water and carbon dioxide with SOEC for syngas production and subsequent upgrading to SNG by methanation. The performance of the P2P system was thoroughly assessed by analyzing the effects of rSOC stack operating parameters (inlet gas temperature, oxidant-to-fuel ratio, oxidant recirculation rate, cell current) and system configurations (pressurized/ambient rSOC operation, air/oxygen as oxidant/sweep fluid) on stack and system efficiency. The analysis allowed to identify the most efficient configuration of the P2P system, and to select the feasible operating currents (i.e., the currents included within the limits given by the physical thermal constraints of SOC materials) for which the highest roundtrip efficiency is achieved. Pressurized rSOC operation (10 bar) with pure oxygen as oxidant/sweep gas and full recirculation of the oxidant flow ensured the highest charging and discharging effectiveness, with a system roundtrip efficiency of 72% when the stack is operating at the maximum efficiency currents (-1.3 A/cm2 in SOEC and 0.3 A/cm2 in SOFC). A dynamic analysis was performed on the rSOC to determine the characteristic times of the thermal response of an SRU coupled with variable loads. The analysis showed that the SOEC is intrinsically more suitable to work with variable loads thanks to the balance between reaction endothermicity and losses exothermicity that reduces the magnitude and the rate of temperature fluctuations originated by current variations. A case study was presented to show the application of P2P with fluctuating RES. In the case study, the sizing of an rSOC-based P2P system designed for the minimization of the imbalance (i.e., the difference between effective and forecasted electricity production) of a 1 MW grid-connected wind farm was performed. An optimal number of cells was found, for which the imbalance is reduced by 77 %. The estimated roundtrip efficiency of the optimal-size P2P system coupled with the wind farm was 54 %. The P2G systems analyzed are composed by three main sections: a hydrogen/syngas production and storage section based on an SOEC stack; a methanation section based on chemical reactors; and an SNG conditioning section for the upgrading of the produced SNG to grid-injection quality. The design and operating conditions of the SOEC section were selected following the results of the analysis performed on the P2P system, and the SNG production section was designed on the basis of a commercial methanation process based on catalytic reactors. The plant efficiency evaluated by simulations was 65.4% for the H2-based P2G and 65.5% for the co-electrolysis based P2G without considering cogeneration or thermal integration between plant sections. Even if the efficiencies were similar for the two P2G configurations, the storage capacity of the H2-based P2G plant was higher, because of the higher operating current achieved by the SOEC stack. The results suggested that even if the co-electrolysis based P2G system presents a slightly higher efficiency, the choice of a H2-based P2G option can ensure a better exploitation of the installed capacity, and also eliminates the risks of carbon-deposition in the stack related to the use of carbon containing mixtures and of stack poisoning related to contaminants potentially present in CO2 streams (e.g., hydrogen sulphide). A case study assessing the effect of H2S poisoning of the SOEC stack on the P2G system performance was also presented. The results presented in this Thesis demonstrated that hydrogen-based P2P with rSOCs is the most efficient solution for local RES storage among the different SOC-based EES options investigated. The high values of roundtrip efficiency achieved demonstrated the competitiveness of rSOC-based P2P also with other large-scale EES options (PHS, CAES). The hydrogen-based P2P is however constrained to on-site applications due to the lack of a hydrogen transport infrastructure, while P2G solutions offer the possibility of transferring the electricity stored in the SNG form through the existing natural gas infrastructure, and also allow the direct use of SNG in already existing technologies (i.e., for mobility, heating, etc.), providing the technological bridge for transferring RES power to other markets different from the electrical one