There seems to be more security events happening on the network nowadays, so the administrators have to be able to find the malicious activities in progress as soon as possible in order to launch effective and efficient countermeasures. The Network administrators need to monitor the networks through collecting real time traffic measurement data on their networks, but they might find that the data gathered seems to be too little or too much detail. SNMP-based tools traditionally adopted most often give too little. However, packet sniffing tools investigate too much, so that the performance is sacrificed, especially on a large network with heavy traffic. Flows are defined as a series of packets traveling between the two communicating end hosts. Flow profiling functionality is built into most networking devices today, which efficiently provide the information required to record network and application resource utilization. Flow strikes a balance between detail and summary. NetFlow is the de facto standard in flow profiling. We introduce¡A describe¡Aand investigate its features, advantages, and strengths. Many useful flow-related tools are freely available on the Internet. A mechanism is proposed to make use of the flow logs to monitor the network effectively and efficiently. Through verification, it is believed that using flow logs can benefit the network administrator so much. The administrators can use them for timely monitoring, DoS and worm propagation detection, forensics et al.

Profiling techniques to detect performance bugs in applications are usually customized to detect a specific bug pattern and involve significant engineering effort. In spite of this effort, many techniques either suffer from high runtime overheads or are imprecise. This necessitates the design of a common and efficient instrumentation substrate that profiles the flow of objects during an execution. Designing such a substrate which enables profile generation precisely with low overhead is non-trivial due to the number of objects created, accessed and paths traversed by them in an execution. In this thesis, we design and implement an efficient instrumentation substrate that efficiently generates object flow profiles for Java programs, without requiring any modifications to the underlying virtual machine. We achieve this by applying Ball-Larus numbering on a specialized hy-brid ow graph (hfg). The hfg path profiles that are collected during runtime are post-processed o ine to derive the object flow profiles. We extend the design to handle inter-procedural objec flows by constructing flow summaries for each method and incorporating them appropriately. We have implemented the substrate and validated its efficacy by applying it on programs from popular benchmark suites including dacapo and java-grande. The results demonstrate the scalability of our approach, which handles 0.2M to 0.55B object accesses with an average runtime overhead of 8x. We also demonstrate the effectiveness of the generated profiles by implementing three client analyses that consume the profiles to detect performance bugs. The analyses are able to detect 38 performance bugs which when refactored result in signi cant performance gains (up to 30%) in running times.

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This thesis deals with the problem of water losses in the Loučenský brook and Bouřlivec basins. It was written on the basis of a project for the state enterprise Povodí Ohře, which dealt with the management of these streams. Loučenský potok and Bouřlivec are the sources of water for the Všechlapy reservoir, which provides a number of functions in the reservoir surroundings. However, the Všechlapy reservoir has been threatened by hydrological drought in recent years. For this reason, it is necessary to determine the water losses in the basin and focus on possible methods to ensure that the reservoir has sufficient water levels to maintain all of its major functions. In the first part of the thesis, the theoretical background related to the issue is explained. In the practical part of the thesis, water losses in the basin are detected mainly on the basis of longitudinal profiling of flows and recorded water withdrawals. Flow measurements were carried out on a total of 43 profiles in five different hydrological conditions with a focus on the dry season. The results show that there is a need to look for reserves in two areas. Firstly, in the management of the ponds, where it appears that a significant amount of water is being lost throughout the basins, and secondly, in the small-scale users who draw...