This document provides information about Cisco NetFlow technology and its usage to protect networks from different types of attacks. Part of the document is a summary of common security risks in term of their detection on network and transport layer. There are specified characteristics of NetFlow data containing samples of security risks. On the basis of these characteristics, an application for detection these risks is designed and implemented.

Master thesis involves the development of quality measurement issues and performance parameters in data networks. It describes the main technologies as they affect the quality and performance parameters and the effect of these parameters for voice, video and data services. Next are listed some methods for measuring parameters of the data network.In the practical part is selected one method of measuring network parameters and properties of this method are demonstrated by illustrative examples.

This document deals with design, implementation and testing of software system for detecting p2p (peer-to-peer) networks based on combination of BPF prefiltering and POSIX regular expressions packet payload matching with known p2p protocol communications. The proposed detection system includes a database with some rules of most effuse p2p protocols in format resembling to definitions for L7-filter classifier. The application is implemented in C, runs in userspace and is targeted to all POSIX compatible platforms. The combination of detector with user attached QoS controlling is complete solution for traffic reduction of common p2p protocols.

This master's thesis addresses processing of flow monitoring records from a point of view of an IPFIX collector. It analysis the current solution of the modular collector, which went through considerable historical development, and focuses on revealing its strengths and weaknesses. Based on acquired knowledge, a new collector is designed. The new solution, which significantly modifies individual components for processing of flow records, focuses on high throughput and adds missing functionalities. The document also compares performance of both generations and the new collector clearly dominates.

This master thesis deals with the problems of memory reduction in the stateful network traffic processing. Its goal is to explore new possibilities of memory reduction during network processing. As an introduction this thesis provides motivation and reasons for need to search new method for the memory reduction. In the following part there are theoretical analyses of NetFlow technology and two basic methods which can in principle reduce memory demands of stateful processing. Later on, there is described the design and implementation of solution which contains the application of these two methods to NetFlow architecture. The final part of this work summarizes the main properties of this solution during interaction with real data.

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 aim of this master's thesis is to design a language through which it would be possible to monitor a stream of network flows in order to detect network policy violations in the local network. An analysis of the languages used in the data stream management systems and an analysis of tasks submitted by the potential administrator were both carried out. The analysis specified resulted in the language design which represents pipelining consisting of filtering and aggregation. These operations can be clearly defined and managed within security rules. The result of this thesis also results in the Policer modul being integrated in the NEMEA system, which is able to apply the main commands of the proposed language. Finally, the module meets the requirements of the specified tasks and may be used for further development in the area of monitoring network policies.

My Master's thesis deals with the problems of flow compression in network devices. Its outcome should alleviate memory consumption of the flows and simplify the processing of network traffic. As an introduction I provide a description of protocols serving for data storage and manipulation, followed by discussion about possibilities of compression methods that are employed nowadays. In the following part there is an in-depth analysis of source data that shows the structure and composition of the data and brings up useful observations, which are later used in the testing  of existing compression methods, as well as about their potential and utilization in flow compression. Later on, I venture into the field of lossy compression and basing on the test results a new approach is described, created by means of flow clustering and their subsequent lossy compression. The conclusion contains an evaluation of the possibilities of the method and the final summary of the thesis along with various suggestions for further development of the research.