Eliminating Software Failures - A Literature Survey

Software faults are expensive and cause serious damage, particularly if discovered late or not at all. Some software faults tend to be hidden. One goal of the thesis is to figure out the status quo in the field of software fault elimination since there are no recent surveys of the whole area. Basis for a structural framework is proposed for this unstructured field, paying attention to compatibility and how to find studies. Bug elimination means are surveyed, including bug knowhow, defect prevention and prediction, analysis, testing, and fault tolerance. The most common research issues for each area are identified and discussed, along with issues that do not get enough attention. Recommendations are presented for software developers, researchers, and teachers. Only the main lines of research are figured out. The main emphasis is on technical aspects. The survey was done by performing searches in IEEE, ACM, Elsevier, and Inspect databases. In addition, a systematic search was done for a few well-known related journals from recent time intervals. Some other journals, some conference proceedings and a few books, reports, and Internet articles have been investigated, too. The following problems were found and solutions for them discussed. Quality assurance is testing only is a common misunderstanding, and many checks are done and some methods applied only in the late testing phase. Many types of static review are almost forgotten even though they reveal faults that are hard to be detected by other means. Other forgotten areas are knowledge of bugs, knowing continuously repeated bugs, and lightweight means to increase reliability. Compatibility between studies is not always good, which also makes documents harder to understand. Some means, methods, and problems are considered method- or domain-specific when they are not. The field lacks cross-field research.

Desempenho físico-químico de metais e estruturas de concreto de redes de distribuição de energia: estudo de caso na região de Manaus

The influence of natural aging furthered by atmospheric corrosion of parts of electric transformers and materials, as well as of concrete poles and cross arms containing corrosion inhibitors was evaluated in Manaus. Results for painted materials, it could showed that loss of specular gloss was more intensive in aliphatic polyurethane points than in acrylic polyurethane ones. No corrosion was observed for metal and concrete samples until 400 days of natural aging. Corrosion in steel reinforcement was noticed in some poles, arising from manufacturing faults, such as low cement content, water/cement ratio, thin concrete cover thickness, etc. The performance of corrosion inhibitors was assessed by many techniques after natural and accelerated aging in a 3.5% saline aqueous solution. The results show the need for better chemical component selection and its concentration in the concrete mixture.

On Fault Tolerance Methods for Networks-on-Chip

Technology scaling has proceeded into dimensions in which the reliability of manufactured devices is becoming endangered. The reliability decrease is a consequence of physical limitations, relative increase of variations, and decreasing noise margins, among others. A promising solution for bringing the reliability of circuits back to a desired level is the use of design methods which introduce tolerance against possible faults in an integrated circuit. This thesis studies and presents fault tolerance methods for network-onchip (NoC) which is a design paradigm targeted for very large systems-onchip. In a NoC resources, such as processors and memories, are connected to a communication network; comparable to the Internet. Fault tolerance in such a system can be achieved at many abstraction levels. The thesis studies the origin of faults in modern technologies and explains the classification to transient, intermittent and permanent faults. A survey of fault tolerance methods is presented to demonstrate the diversity of available methods. Networks-on-chip are approached by exploring their main design choices: the selection of a topology, routing protocol, and flow control method. Fault tolerance methods for NoCs are studied at different layers of the OSI reference model. The data link layer provides a reliable communication link over a physical channel. Error control coding is an efficient fault tolerance method especially against transient faults at this abstraction level. Error control coding methods suitable for on-chip communication are studied and their implementations presented. Error control coding loses its effectiveness in the presence of intermittent and permanent faults. Therefore, other solutions against them are presented. The introduction of spare wires and split transmissions are shown to provide good tolerance against intermittent and permanent errors and their combination to error control coding is illustrated. At the network layer positioned above the data link layer, fault tolerance can be achieved with the design of fault tolerant network topologies and routing algorithms. Both of these approaches are presented in the thesis together with realizations in the both categories. The thesis concludes that an optimal fault tolerance solution contains carefully co-designed elements from different abstraction levels

Testausmenetelmien ja testauksen lähestymistapojen valintaperusteet kirjallisuudessa

Testaustapausten valitseminen on testauksessa tärkeää, koska kaikkia testaustapauksia ei voida testata aika- ja raharajoitteiden takia. Testaustapausten valintaan on paljon eri menetelmiä joista eniten esillä olevat ovat malleihin perustuva valinta, kombinaatiovalinta ja riskeihin perustuva valinta. Kaikkiin edellä mainittuihin menetelmiin testaustapaukset luodaan ohjelman spesifikaation perusteella. Malleihin perustuvassa menetelmässä käytetään hyväksi ohjelman toiminnasta olevia malleja, joista valitaan tärkeimmät testattavaksi. Kombinaatiotestauksessa testitapaukset on muodostettu ominaisuuspareina jolloin yhden parin testaamisesta päätellään kahden ominaisuuden toiminta. Kombinaatiotestaus on tehokas löytämään virheitä, jotka johtuvat yhdestä tai kahdesta tekijästä. Riskeihin perustuva testaus pyrkii arvioimaan ohjelman riskejä ja valitsemaan testitapaukset niiden perusteella. Kaikissa menetelmissä priorisointi on tärkeässä roolissa, jotta testauksesta saadaan riittävä luotettavuus ilman kustannusten nousua.

Combined dielectrophoretic and impedance system for on-chip controlled bacteria concentration: Application to Escherichia coli

The present paper reports a bacteria autonomous controlled concentrator prototype with a user-friendly interface for bench-top applications. It is based on a micro-fluidic lab-on-a-chip and its associated custom instrumentation, which consists in a dielectrophoretic actuator, to pre-concentrate the sample, and an impedance analyser, to measure concentrated bacteria levels. The system is composed by a single micro-fluidic chamber with interdigitated electrodes and a instrumentation with custom electronics. The prototype is supported by a real-time platform connected to a remote computer, which automatically controls the system and displays impedance data used to monitor the status of bacteria accumulation on-chip. The system automates the whole concentrating operation. Performance has been studied for controlled volumes of Escherichia coli (E. coli) samples injected into the micro-fluidic chip at constant flow rate of 10 μL/min. A media conductivity correcting protocol has been developed, as the preliminary results showed distortion of the impedance analyser measurement produced by bacterial media conductivity variations through time. With the correcting protocol, the measured impedance values were related to the quantity of bacteria concentrated with a correlation of 0.988 and a coefficient of variation of 3.1%. Feasibility of E. coli on-chip automated concentration, using the miniaturized system, has been demonstrated. Furthermore, the impedance monitoring protocol had been adjusted and optimized, to handle changes in the electrical properties of the bacteria media over time.

Methods and Models for Accelerating Dynamic Simulation of Fluid Power Circuits

The objective of this dissertation is to improve the dynamic simulation of fluid power circuits. A fluid power circuit is a typical way to implement power transmission in mobile working machines, e.g. cranes, excavators etc. Dynamic simulation is an essential tool in developing controllability and energy-efficient solutions for mobile machines. Efficient dynamic simulation is the basic requirement for the real-time simulation. In the real-time simulation of fluid power circuits there exist numerical problems due to the software and methods used for modelling and integration. A simulation model of a fluid power circuit is typically created using differential and algebraic equations. Efficient numerical methods are required since differential equations must be solved in real time. Unfortunately, simulation software packages offer only a limited selection of numerical solvers. Numerical problems cause noise to the results, which in many cases leads the simulation run to fail. Mathematically the fluid power circuit models are stiff systems of ordinary differential equations. Numerical solution of the stiff systems can be improved by two alternative approaches. The first is to develop numerical solvers suitable for solving stiff systems. The second is to decrease the model stiffness itself by introducing models and algorithms that either decrease the highest eigenvalues or neglect them by introducing steady-state solutions of the stiff parts of the models. The thesis proposes novel methods using the latter approach. The study aims to develop practical methods usable in dynamic simulation of fluid power circuits using explicit fixed-step integration algorithms. In this thesis, twomechanisms whichmake the systemstiff are studied. These are the pressure drop approaching zero in the turbulent orifice model and the volume approaching zero in the equation of pressure build-up. These are the critical areas to which alternative methods for modelling and numerical simulation are proposed. Generally, in hydraulic power transmission systems the orifice flow is clearly in the turbulent area. The flow becomes laminar as the pressure drop over the orifice approaches zero only in rare situations. These are e.g. when a valve is closed, or an actuator is driven against an end stopper, or external force makes actuator to switch its direction during operation. This means that in terms of accuracy, the description of laminar flow is not necessary. But, unfortunately, when a purely turbulent description of the orifice is used, numerical problems occur when the pressure drop comes close to zero since the first derivative of flow with respect to the pressure drop approaches infinity when the pressure drop approaches zero. Furthermore, the second derivative becomes discontinuous, which causes numerical noise and an infinitely small integration step when a variable step integrator is used. A numerically efficient model for the orifice flow is proposed using a cubic spline function to describe the flow in the laminar and transition areas. Parameters for the cubic spline function are selected such that its first derivative is equal to the first derivative of the pure turbulent orifice flow model in the boundary condition. In the dynamic simulation of fluid power circuits, a tradeoff exists between accuracy and calculation speed. This investigation is made for the two-regime flow orifice model. Especially inside of many types of valves, as well as between them, there exist very small volumes. The integration of pressures in small fluid volumes causes numerical problems in fluid power circuit simulation. Particularly in realtime simulation, these numerical problems are a great weakness. The system stiffness approaches infinity as the fluid volume approaches zero. If fixed step explicit algorithms for solving ordinary differential equations (ODE) are used, the system stability would easily be lost when integrating pressures in small volumes. To solve the problem caused by small fluid volumes, a pseudo-dynamic solver is proposed. Instead of integration of the pressure in a small volume, the pressure is solved as a steady-state pressure created in a separate cascade loop by numerical integration. The hydraulic capacitance V/Be of the parts of the circuit whose pressures are solved by the pseudo-dynamic method should be orders of magnitude smaller than that of those partswhose pressures are integrated. The key advantage of this novel method is that the numerical problems caused by the small volumes are completely avoided. Also, the method is freely applicable regardless of the integration routine applied. The superiority of both above-mentioned methods is that they are suited for use together with the semi-empirical modelling method which necessarily does not require any geometrical data of the valves and actuators to be modelled. In this modelling method, most of the needed component information can be taken from the manufacturer’s nominal graphs. This thesis introduces the methods and shows several numerical examples to demonstrate how the proposed methods improve the dynamic simulation of various hydraulic circuits.

Spectrometrical Monitoring of Laser Sintering Process of Ceramic Material

This thesis is done as a part of project called FuncMama that is a project between Technical Research Centre of Finland (VTT), Oulu University (OY), Lappeenranta University of Technology (LUT) and Finnish industrial partners. Main goal of the project is to manufacture electric and mechanical components from mixed materials using laser sintering. Aim of this study was to create laser sintered pieces from ceramic material and monitor the sintering event by using spectrometer. Spectrometer is a device which is capable to record intensity of different wavelengths in relation with time. In this study the monitoring of laser sintering was captured with the equipment which consists of Ocean Optics spectrometer, optical fiber and optical lens (detector head). Light from the sintering process hit first to the lens system which guides the light in to the optical fibre. Optical fibre transmits the light from the sintering process to the spectrometer where wavelengths intensity level information is detected. The optical lens of the spectrometer was rigidly set and did not move along with the laser beam. Data which was collected with spectrometer from the laser sintering process was converted with Excel spreadsheet program for result’s evaluation. Laser equipment used was IPG Photonics pulse fibre laser. Laser parameters were kept mainly constant during experimental part and only sintering speed was changed. That way it was possible to find differences in the monitoring results without fear of too many parameters mixing together and affecting to the conclusions. Parts which were sintered had one layer and size of 5 x 5 mm. Material was CT2000 – tape manufactured by Heraeus which was later on post processed to powder. Monitoring of different sintering speeds was tested by using CT2000 reference powder. Moreover tests how different materials effect to the process monitoring were done by adding foreign powder Du Pont 951 which had suffered in re-grinding and which was more reactive than CT2000. By adding foreign material it simulates situation where two materials are accidently mixed together and it was studied if that can be seen with the spectrometer. It was concluded in this study that with the spectrometer it is possible to detect changes between different laser sintering speeds. When the sintering speed is lowered the intensity level of light is higher from the process. This is a result of higher temperature at the sintering spot and that can be noticed with the spectrometer. That indicates it could be possible to use spectrometer as a tool for process observation and support the idea of having system that can help setting up the process parameter window. Also important conclusion was how well the adding of foreign material could be seen with the spectrometer. When second material was added a significant intensity level raise could be noticed in that part where foreign material was mixed. That indicates it is possible to see if there are any variations in the material or if there are more materials mixed together. Spectrometric monitoring of laser sintering could be useful tool for process window observation and temperature controlling of the sintering process. For example if the process window for specific material is experimentally determined to get wanted properties and satisfying sintering speed. It is possible if the data is constantly recorded that the results can show faults in the part texture between layers. Changes between the monitoring data and the experimentally determined values can then indicate changes in the material being generated by material faults or by wrong process parameters. The results of this study show that spectrometer could be one possible tool for monitoring. But to get in that point where this all can be made possible much more researching is needed.

Painelaitteiden kunnonvalvonta ja kemikaaliputkistojen rakennuttaminen

Painelaitteet ja kemikaaliputkistot ovat yleisiä varsinkin kemian alan yrityksissä. Omista-jan ja haltijan on tiedettävä niihin liittyvä lainsäädäntö, ja osattava soveltaa niitä käytän-töön. Työssä on selvitetty painelaitteisiin ja kemikaaliputkistoihin liittyvän lainsäädännön olen-naisin sisältö. Nykyisin painelaitteiden määräaikaistarkastuksia voidaan korvata painelait-teen seurannalla ja kunnonvalvontajärjestelmällä. Mitä se käytännössä tarkoittaa, ja onko Suomessa mahdollisuutta kuinka laajasti hyödynnetty? On tärkeää tuntea painelaitteiden ja kemikaaliputkistojen vikaantumismekanismit ja kunnonvalvontamenetelmät, jotta yritys voi luoda omaan toimintaympäristöön soveltuvan kunnonvalvontajärjestelmän tai paine-laitteiden seurannan. On pyrittävä siihen, että ongelmat havaitaan, ennen kuin vaurio syn-tyy. Kunnonvalvontajärjestelmän luomiseen ja ylläpitoon voidaan hyödyntää painelaittei-den riskiperusteiseen kunnossapitoon ja tarkastukseen tarkoitettua menettelyä. Työssä on tarkemmin käyty läpi menettelyn sisältö. Kustannustehokkuus ja tuotantolaitteiden käytettävyys ovat nousseet tärkeiksi osa-alueiksi kilpailukyvyn takaamiseksi. Painelaitteiden tarkastuksista ja muista painelaitteisiin ja ke-mikaaliputkistoihin liittyvistä ennakkohuolloista syntyvät kustannukset ovat merkittäviä. Näihin kohdistuvia kustannussäästöjä voidaan saavuttaa monin keinoin huonontamatta kuitenkaan turvallisuutta. Työssä on selvitetty kohdeyrityksen painelaitteet ja kemikaali-putkistot. Lisäksi on käyty läpi nykyinen tarkastusjaksotus, keskeisimmät viat ja tarkastuk-siin liittyvää kustannushistoriaa. Lopputuloksena on syntynyt esiselvitys ja kemikaaliputkistojen hankkimista helpottavaa tietoa. Esiselvityksen avulla kohdeyritys voi yhdessä kunnossapitoyrityksen kanssa laatia strategian painelaitteiden kunnossapidolle ja tarkastuksille. Merkittäviä kustannussäästöjä on saavutettavissa ehdotetuilla jatkotoimenpiteillä, vaikka päädyttäisiin edelleen painelait-teiden tarkastuksien osalta noudattamaan olemassa olevaa käytäntöä.

Integration of microgrids into electricity distribution networks

Existing electricity distribution system is under pressure because implementation of distributed generation changes the grid configuration and also because some customers demand for better distribution reliability. In a short term, traditional network planning does not offer techno-economical solutions for the challenges and therefore the idea of microgrids is introduced. Islanding capability of microgrids is expected to enable better reliability by reducing effects of faults. The aim of the thesis is to discuss challenges in integration of microgrids into distribution networks. Study discusses development of microgrid related smart grid features and gives estimation of the guideline of microgrid implementation. Thesis also scans microgrid pilots around the world and introduces the most relevant projects. Analysis reveals that the main focus of researched studies is on low voltage microgrids. This thesis extends the idea to medium voltage distribution system and introduces challenges related to medium voltage microgrid implementation. Differences of centralized and distributed microgrid models are analyzed and the centralized model is discovered to be easiest to implement into existing distribution system. Preplan of medium voltage microgrid pilot is also carried out in this thesis.

Hevonen irtaimen kaupan tapauksena - laatuvirhe ja siihen varautuminen

Tutkimuksessa tarkastellaan hevoskauppaa ja sen erityispiirteitä suhtees-sa irtaimen kauppaa säätelevään lainsäädäntöön. Tavoitteena on tuoda esiin hevosesta johtuvia erityispiirteitä ja pohtia sovellettavan lainsäädän-nön soveltuvuutta hevosen kauppaan. Tarkastelu kohdentuu erityisesti hevoselle ominaisiin laatuvirheen muotoihin, kuten sairauksiin ja fyysisiin vikoihin. Lisäksi tarkastellaan, miten esiin nostettuihin erityispiirteisiin on varauduttu hevoskauppaan tarkoitetuissa kauppasopimusmalleissa. Hevoskauppaan pätee sama lainsäädäntö kuin minkä tahansa muun ir-taimen tavaran kauppaan. Virheeseen varautuminen yksityiskohtaisesti sopimalla korostuu hevoskaupassa, koska täydellistä ja virheetöntä hevosta ei ole olemassakaan. Myyjän näkökulmasta onnistuneessa kauppaprosessissa neuvotellaan virheen mahdollisuus niin pieneksi kuin se on mahdollista. Tähän instrumentit antavat lainsäädäntö ja erityisesti sopimusoikeudelliset keinot. Ostajan näkökulmasta onnistuneessa kaupassa hän on kyennyt asiantuntijoihin tukeutuen tunnistamaan ennalta hevosen viat ja muut epämieluisat ominaisuudet. Nämä tiedostaen ostaja määrittää, mitä virheitä on valmis hyväksymään. Hevoskaupassa riidan välittömät ja välilliset kustannukset suhteessa maksettuun kauppahintaan voivat nousta korkeiksi. Hevoskaupassa usein ainoa kirjallinen dokumentti on omistajanvaihdosilmoitus, eikä kauppasopimuksen laatiminen kirjallisena ole itsestäänselvyys. Yksinomaan hevoskauppaan liittyvien juridisten kysymysten tekeminen näkyväksi on tärkeää. Irtaimen kauppaa säätelevä lainsäädäntö ei kuitenkaan tunnista riittävällä tarkkuudella hevosen erityispiirteitä persoonaesineenä, vaan väliin tarvi-taan vakiosopimusten kaltaisia apuvälineitä kaupan osapuolten tueksi.

Katsastuksen teknisen laadun mittaaminen ja johtaminen

Suorituskyvyn mittaamisella on monia myönteisiä vaikutuksia koko organisaation toimintaan. Mittaamisen avulla toimintaa voidaan johtaa haluttuun suuntaan. Tutkimuksen tavoitteena oli tutkia, minkälainen suorituskykymittaristo tarvitaan katsastusyrityksen ylimmän johdon käyttöön, jotta katsastuksen teknisen laadun johtaminen mahdollistuisi. Tutkimuksen tarkoituksena oli rakentaa katsastuksen teknisen laadun suorituskykymittaristo ylimmälle johdolle. Katsastuksen tekninen laatu on keskeinen kysymys katsastusyritysten olemassaololle. Tekninen laatu on koko katsastustoiminnan perusta, jonka päälle liiketoiminta voidaan rakentaa. Ilman tätä perustaa ei ole jatkuvuutta liiketoiminnalle. Teknisen laadun mittaaminen ei kuitenkaan ole tällä hetkellä järjestelmällistä, eikä käytettävissä ole ollut tehtävään soveltuvaa mittaristoa. Tutkimuksessa käytettiin A-Katsastus Oy:n vuosien 2008–2011 aikana syntyneitä katsastustilastoja. Tilastollista prosessin valvonta-menetelmää (SPC) soveltamalla määritettiin toimipaikka- ja katsastajakohtaiset valvontarajat hylkäysprosenteille ja vikojen määrille. Valvontarajojen avulla rakennettiin katsastuksen teknisen laadun suorituskykymittaristo toimiala-, yritys-, toimipaikka- ja katsastajatasoille. Mittariston avulla voidaan asettaa tekniselle laadulle tavoitteet, seurata tavoitteiden toteumaa ja käynnistää tarvittaessa korjaavat toimenpiteet.

On Dynamic Monitoring Methods for Networks-on-Chip

Rapid ongoing evolution of multiprocessors will lead to systems with hundreds of processing cores integrated in a single chip. An emerging challenge is the implementation of reliable and efficient interconnection between these cores as well as other components in the systems. Network-on-Chip is an interconnection approach which is intended to solve the performance bottleneck caused by traditional, poorly scalable communication structures such as buses. However, a large on-chip network involves issues related to congestion problems and system control, for instance. Additionally, faults can cause problems in multiprocessor systems. These faults can be transient faults, permanent manufacturing faults, or they can appear due to aging. To solve the emerging traffic management, controllability issues and to maintain system operation regardless of faults a monitoring system is needed. The monitoring system should be dynamically applicable to various purposes and it should fully cover the system under observation. In a large multiprocessor the distances between components can be relatively long. Therefore, the system should be designed so that the amount of energy-inefficient long-distance communication is minimized. This thesis presents a dynamically clustered distributed monitoring structure. The monitoring is distributed so that no centralized control is required for basic tasks such as traffic management and task mapping. To enable extensive analysis of different Network-on-Chip architectures, an in-house SystemC based simulation environment was implemented. It allows transaction level analysis without time consuming circuit level implementations during early design phases of novel architectures and features. The presented analysis shows that the dynamically clustered monitoring structure can be efficiently utilized for traffic management in faulty and congested Network-on-Chip-based multiprocessor systems. The monitoring structure can be also successfully applied for task mapping purposes. Furthermore, the analysis shows that the presented in-house simulation environment is flexible and practical tool for extensive Network-on-Chip architecture analysis.

Formal development and quantitative verification of dependable systems

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Taloushallinnon eettiset ongelmat verotarkastuskertomuksista tehtyjen havaintojen perusteella

Tässä tutkielmassa tutkittiin taloushallinnon eettisiä ongelmakohtia käyttäen aineistona verotarkastuskertomuksia. Tutkielman tavoitteena oli selvittää onko taloushallinnon eettisissä ratkaisuissa kyse kirjanpitäjän vai yrittäjän etiikasta, voidaanko verotarkastuksella havaitut virheet jaotella tahallisiin ja tahattomiin ja voidaanko näistä virheistä tehdä johtopäätöksiä veronmaksumyönteisyydestä. Kirjanpitäjän ja yrittäjän etiikan havaittiin ilmenevän eri tavoilla. Jos etiikkaa pohdittiin veronmaksuhalukkuuden merkityksessä, niin tällöin kyse oli yrittäjän etiikasta. Verotarkastuksilla havaitut virheet jaoteltiin virhetyyppeihin, joita käytettiin veronmaksumyönteisyyden analysointiin. Tutkielmassa käytettyjä virhetyyppejä olivat muun muassa luontois- ja henkilökuntaedut, kustannusten korvaukset ja edustusmenot. Veronmaksumyönteisyydessä havaittiin selviä eroja eri virhetyyppien välillä. Suurin osa virhetyypeistä kuului veronmaksumyönteisyyden perusteella joukkoon, jossa lakeja noudatetaan vain valvonnan alaisena. Näitä virheitä tekevien kohdalla verovalvonnan kattavuudella saavutetaan parhaat tulokset.

Adaptive Routing Approaches for Networked Many-Core Systems

Through advances in technology, System-on-Chip design is moving towards integrating tens to hundreds of intellectual property blocks into a single chip. In such a many-core system, on-chip communication becomes a performance bottleneck for high performance designs. Network-on-Chip (NoC) has emerged as a viable solution for the communication challenges in highly complex chips. The NoC architecture paradigm, based on a modular packet-switched mechanism, can address many of the on-chip communication challenges such as wiring complexity, communication latency, and bandwidth. Furthermore, the combined benefits of 3D IC and NoC schemes provide the possibility of designing a high performance system in a limited chip area. The major advantages of 3D NoCs are the considerable reductions in average latency and power consumption. There are several factors degrading the performance of NoCs. In this thesis, we investigate three main performance-limiting factors: network congestion, faults, and the lack of efficient multicast support. We address these issues by the means of routing algorithms. Congestion of data packets may lead to increased network latency and power consumption. Thus, we propose three different approaches for alleviating such congestion in the network. The first approach is based on measuring the congestion information in different regions of the network, distributing the information over the network, and utilizing this information when making a routing decision. The second approach employs a learning method to dynamically find the less congested routes according to the underlying traffic. The third approach is based on a fuzzy-logic technique to perform better routing decisions when traffic information of different routes is available. Faults affect performance significantly, as then packets should take longer paths in order to be routed around the faults, which in turn increases congestion around the faulty regions. We propose four methods to tolerate faults at the link and switch level by using only the shortest paths as long as such path exists. The unique characteristic among these methods is the toleration of faults while also maintaining the performance of NoCs. To the best of our knowledge, these algorithms are the first approaches to bypassing faults prior to reaching them while avoiding unnecessary misrouting of packets. Current implementations of multicast communication result in a significant performance loss for unicast traffic. This is due to the fact that the routing rules of multicast packets limit the adaptivity of unicast packets. We present an approach in which both unicast and multicast packets can be efficiently routed within the network. While suggesting a more efficient multicast support, the proposed approach does not affect the performance of unicast routing at all. In addition, in order to reduce the overall path length of multicast packets, we present several partitioning methods along with their analytical models for latency measurement. This approach is discussed in the context of 3D mesh networks.