Recent research results on buffer sizing challenged the widely used assumption that routers should buffer millions of packets. These new results suggest that when smooth Transmission Control Protocol (TCP) traffic goes through a single tiny buffer of size O(logW), then close-to-peak throughput can be achieved where W is the maximum window size of TCP flows. But the current routers have the buffer size much larger than that. It is shown that, we can reduce the buffer size by a factor of √N when the traffic is somehow smooth, where N is the number of flows. So, the main goal of this thesis is to show some directions on how the buffer size can be reduced in Internet routers. In this research, we adopted some measures like different packet sizes, different network scenarios, different buffer sizes, various link delays to see the performance of small buffers with the presence of both TCP and UDP traffic. / Graduate

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While developing networking for games and applications, developers have a list of network specific requirements to be met as well as decide how to meet them. It is not always easy to decide what protocol is best suited for a given network configuration, or what is the best size of a data packet. By performing a comparative analysis, it becomes possible to identify how protocols, packet size, and network configuration impact the one-way travel time and throughput of a given implementation. The result shows how the different implementations compared against each other and the analysis tries to determine why they perform as they do. This gives a good overview of the pros and cons of how TCP, TCP(N), UDP, and RakNet, behave and perform over LANs and WLANs with varying packet size.

Cognitive Radio (CR) has emerged as the key technology to enable dynamic spectrum access. Capabilities of CR can meet the unique requirements of many wireless networks. Hence, Cognitive Radio Sensor Networks (CRSN) is introduced as a promising solution to address the unique challenges of Wireless Sensor Networks (WSN) which have been widely used for reliable event detection for many applications. However, there exist many open research issues for the realization of CRSN. Among others, determination of optimal packet size for CRSN is one of the most fundamental problems to be addressed. The existing optimal packet size solutions devised for CR networks as well as WSN are not applicable in CRSN regime and would cause a waste of energy resources. Hence, the objective of this thesis is to determine the optimal packet size for CRSN that maximizes energy-efficiency while maintaining acceptable interference level for licensed primary users (PU) and remaining under the maximum allowed distortion level between tracked event signal and its estimation at sink. Energy-efficient packet size reduces energy consumption and increases the transmission efficiency for CRSN. In this thesis, the energy-efficient packet size optimization problem is analytically formulated. Then, sequential quadratic programming (SQP) method is used for solving the optimization problem. The variation of optimal packet size with respect to different parameters of CRSN network is observed through numerical analysis. Results reveal that PU behavior and channel bit error rate (BER) are the most critical parameters in determining energy-efficient optimal packet size for CRSN.

Modern applications commonly make use of several subsystems, usually a frontend and a backend. The communication link between these subsystems is commonly an API. Different APIs such as REST and SOAP have been around for a long time but with the increasing use of internet, other techniques as GraphQL have been developed to compensate for older techniques. The aim of this thesis is to measure the performance of GraphQL and how it compares to SOAP and REST and how the overhead reduction of GraphQL will affect the performance. The main method used to evaluate the performance differences between GraphQL, REST and SOAP is an experiment. The results show that GraphQL has the worst performance in all test cases. GraphQL has the lowest packet size out of all three APIs when only a few fields are fetched, however the packet size increases rapidly when multiple fields are requested.

The Information and Communication Technology (ICT) industry and network researchers use traffic generator tools to a large extent to test their systems. The industry uses reliable and rigid hardware-based platform tools for high-performance network testing. The research community commonly uses software-based tools in, for example, experiments because of economic and flexibility aspects. As a result, it is possible to run these tools on different systems and hardware. In this thesis, we examine the software traffic generators Iperf, Mausezahn, Ostinato in a closed loop physical and virtual environment to evaluate the applicability of the tools and find sources of inaccuracy for a given traffic profile. For each network tool, we measure the throughput from 64- to 4096-byte in packet sizes. Also, we encapsulate each tool with container technology using Docker to reach a more reproducible and portable research. Our results show that the CPU primarily limits the throughput for small packet sizes, and saturates the 1000 Mbps link for larger packet sizes. Finally, we suggest using these tools for simpler and automated network tests. / IT-branschen och nätverksforskare använder sig av trafikgeneratorer till stor del för att testa sina system. Industrin använder sig av stabila och pålitliga hårdvaruplattformar för högpresterande nätverkstester. Forskare brukar använda mjukvarubaserade verktyg i till exempel experiment på grund av ekonomiska och flexibilitet skäl. Det är därför möjligt att använda dessa verktyg på olika system och hårdvaror. I denna avhandling undersöker vi mjukvarutrafikgeneratorerna Iperf, Mausezahn, Ostinato i en isolerad fysisk och virtuell miljö, det vill säga för att utvärdera användbarheten av verktygen och hitta felkällor för en given trafikprofil. För varje nätverksverktyg mäter vi genomströmningen från 64 till 4096 byte i paketstorlekar. Dessutom paketerar vi varje verktyg med molnteknologin Docker för att nå ett mer reproducerbart och portabelt arbete. Våra resultat visar att processorn begränsar genomströmningen för små paketstorlekar och saturerar 1000 Mbps-länken för större paketstorlekar. Slutligen föreslår vi att man kan använda dessa verktyg för enklare och automatiserade nätverkstester.

Abstract This research work focuses on how to improve the toughness of heat affected zones (HAZs) of low heat input welds in the case of high strength thermomechanically processed (TMCP) and recrystallization controlled rolled and accelerated cooled (RCR) plates with yield strengths of 355–500 MPa. Experimental work was aimed at the investigation of the intragranular nucleation of acicular ferrite or bainite in hot-rolled plates and the evaluation of the Charpy V and CTOD toughness of the most critical sub-zones of the weld HAZ using simulated specimens with a cooling time t8/5 = 5 s. The zones studied were the coarse grained HAZ (CGHAZ), the intercritically reheated coarse-grained HAZ (ICCGHAZ) and the intercritical HAZ (ICHAZ), the metallographical analyses consisted of microstructural investigations complemented with hardness measurements. Optical, scanning and transmission electron microscopy techniques were employed together with image and electron backscatter diffraction (EBSD) analysis. The test results showed that the toughness of the various sub-zones of the HAZ is improved by promoting intragranularly nucleated ferritic-bainitic (acicular) microstructure in both the CGHAZ and in the base plate. In this way, the sub-zones subjected to intercritical thermal cycles (the ICCGHAZ and the ICHAZ) develop evenly distributed M-A constituents between ferrite and bainite laths. These favourable microstructures can be achieved by using titanium killing or by avoiding niobium microalloying by using copper plus nickel alloying instead. In the laboratory experiments titanium killed steel, containing titanium-manganese oxide/manganese sulphide inclusions with a number density of 300–750 particles/mm2, develops a largely acicular ferritic microstructure in the base plate provided the austenite grain size is greater than about 120 μm and the cooling rate is in the range 6–11 °C/s down to 500 °C. Under plate mill conditions, no significant amount of acicular ferrite could be obtained, because it was not possible to achieve austenite grain sizes larger than about 70 μm after rolling. However, a significant fraction of acicular ferritic-bainitic microstructure was achieved in the CGHAZ, when the austenite grain size exceeded 90 μm. When achieved, a uniform distribution of M-A particles in an acicular ferritic-bainitic microstructure improves toughness. Cracks nucleate at numerous sites on M-A/ferrite boundaries or bainite packet interfaces, but they are initially arrested in the acicular matrix. Crack growth finally occurs by linking of the numerous arrested microcracks.

Wireless sensor networks (WSN) are event based systems that rely on the collective effort of densely deployed sensor nodes continuously observing a physical phenomenon. The spatio-temporal correlation between the sensor observations and the cross-layer design advantages are significant and unique to the design of WSN. Due to the high density in the network topology, sensor observations are highly correlated in the space domain. Furthermore, the nature of the energy-radiating physical phenomenon constitutes the temporal correlation between each consecutive observation of a sensor node. This unique characteristic of WSN can be exploited through a cross-layer design of communication functionalities to improve energy efficiency of the network. In this thesis, several key elements are investigated to capture and exploit the correlation in the WSN for the realization of advanced efficient communication protocols. A theoretical framework is developed to capture the spatial and temporal correlations in WSN and to enable the development of efficient communication protocols. Based on this framework, spatial Correlation-based Collaborative Medium Access Control (CC-MAC) protocol is described, which exploits the spatial correlation in the WSN in order to achieve efficient medium access. Furthermore, the cross-layer module (XLM), which melts common protocol layer functionalities into a cross-layer module for resource-constrained sensor nodes, is developed. The cross-layer analysis of error control in WSN is then presented to enable a comprehensive comparison of error control schemes for WSN. Finally, the cross-layer packet size optimization framework is described.