Cette thèse étudie des problèmes de contrôle d'accès et de qualité de service (QdS) dans les réseaux ad hoc utilisant la norme IEEE 802.11. Dans la première partie de notre travail, nous proposons des améliorations pour la norme 802.11 de base qui ne tient pas compte de la QdS. Au niveau du contrôle d'admission, nous proposons un algorithme d'ordonnancement des flux multimédia qui attribue la priorité aux paquets de manière moins stricte que dans l'algorithme EDF et nous comparons les deux algorithmes par simulation. Au niveau du contrôle d'accès, nous proposons un algorithme qui modifie dynamiquement la fenêtre de contention, et nous effectuons des simulations pour montrer l'amélioration de l'équité entre les stations. Nous nous intéressons par la suite à la différenciation des services, et nous étudions la coexistence de deux classes de service, dont les fenêtres de contention évoluent de manière différente, et évaluons leurs performances en termes de débit et de délai moyen. Ce qui nous amène, dans la deuxième partie de notre travail, à présenter une étude complète de la différenciation des services de l'amendement 802.11e. Nous proposons un cadre analytique général modélisant la méthode d'accès EDCA à l'aide de chaînes de Markov, et définissons quatre méthodes de différenciation, et évaluons les performances des classes en termes de débit, délai moyen et taux de perte. Des approximations pour les réseaux de grande taille nous ont permis d'obtenir, pour un indice de performance fixé, une expression simple de celui de toutes classes en fonction de celui de l'une d'entre elles. Nous déterminons ensuite la relation entre les différents indices de performance des classes, et comparons les différentes méthodes de différenciation, malgré la nature différente de leurs paramètres. De plus, nous établissons analytiquement et vérifions par simulation les conditions d'équivalence, entre les méthodes de différenciation basées sur la distribution du temps de retrait, qui produisent les mêmes performances en termes de débit, délai moyen et taux de perte. Et dans ces conditions, nous analysons l'effet du choix de la distribution sur la gigue. Nos résultats représentent des outils importants pour l'aide à la décision en vue d'atteindre des objectifs de QdS. / This thesis deals with access control and quality of service (QoS) issues in ad hoc networks. In the first part, we propose enhancements of the legacy 802.11 standard which lacks of QoS. For admission control, we propose a scheduling algorithm for multimedia traffic, in which priority is provided to packets with a less strict way than the EDF algorithm, and we compare both algorithms by simulation. For access control, we propose an algorithm that tunes dynamically the contention window, and we use simulations to show improvement of fairness between stations. Then we are interested in service differentiation, and we analyze the coexistence of two service classes having their contention window evolving in different ways, and we evaluate their performances in terms of throughput and mean delay. This leads us, in the second part of this thesis, to present a complete study of service differentiation in the 802.11e amendment. We propose a general analytical framework in which we model the EDCA access scheme by Markov chains. We define and study four differentiation schemes and evaluate class performances in terms of throughput, mean delay and drop ratio. Using approximations for large networks, we derive, for a given class performance index, a simple expression of this index in the other classes. That allows us to determine the relationship between class performances, and compare the differentiation schemes even if the nature of their parameters is different. Moreover, we determine analytically and verify by simulation equivalence conditions, between differentiation schemes based on backoff time distribution, that produce the same performances in terms of throughput, mean delay and drop ratio. Then, in these conditions, we analyze the effect of backoff time distribution on jitter. Our results are important tools for decision making in order to meet QoS objectives.

The aim of this thesis was to create a web application used for centralized management and configuration of wireless networks on access points running on OpenWrt distribution. The reader is acquainted with common principles of wireless networks including description of existing solutions for their centralized management. After that the thesis introduces the reader to OpenWrt distribution and to a method of its configuration using UCI model. The reader is then introduced to the main technologies used in this thesis. Author further describes architecture, user interface and implementation of the web application. The created web application is platform agnostic and provides easy way to manage and configure access points with OpenWrt distribution.

This work describes security mechanisms of wireless network based on 802.11 standard and security enhancement 802.11i of these networks known as WPA2, where the analysis of vulnerabilities and attacks on these networks were performed. The work discusses two major security issues. The first is unsecure management frames responsible for vulnerability with direct impact on availability and the other is the vulnerability that allows executing the impersonalize type of attacks. The system for generation attacks was designed to realize any attack very fast and efficient. The core of the thesis is the design of a system for attack analysis using the principle of trust and reputation computation. The conclusion of the work is devoted to experimenting with the proposed system, especially with the selection of suitable metrics for calculating the trust value.

This work describes available and used standards, protocols and mechanisms used to secure IEEE 802.11 wireless networks. In the next section are listed vulnerabilities and possible attacks against different types of security. The principles of individual attacks on authentication, WEP security and WPA/WPA2 personal mode are described and realized using various software especially linux program aircrack-ng. Password for WEP security is obtained by passive eavesdropping data, using ARP replay injection and by creating own frames. The last two methods are used to generate traffic on the network, which is captured and then used to derive the WEP password. By injecting ARP frames, password was found in the number 60 000 captured frames and about 180 000 frames of data was needed for passive method. Decryption of WEP frame was done by fragment and KoreK chopchop attacks. This decrypted frame could be used to create fake frames and obtain WEP password. Brute force attack is realized for security WPA (WPA2) personal mode (often due to lack of strong password) by comparing password (passphrase) from password list. Speed of comparing is about 200 passwords/s.

This master thesis deals with all types of wireless networks security – in personal, local, metropolitan and also mobile networks. This work is mostly focused on wireless local area networks (WLANs), which are the most widespread at nowadays. This work describes attacks to the wireless local area network, attackers steps and possible protection against it. Some of these attacks are tested in practical part of this work. In this master thesis there were also designed and created two laboratory exercises. One of them is a simulation in the wireless network using Opnet Modeler application. The other exercise is strictly practical type.

Master´s thesis „Security risks of wireless access networks“ deals with wireless access networks, which are the most widespread in this time. The main target is realization of attacks wireless access networks protected by various using methods. This thesis shows main securities gaps, which originate from project this networks. These securities gaps are used for realization attacts in practical part. In the next part I took attention of network´s monitoring possibilities.

Wireless networks are currently the frequent access connection to the local network or the Internet. Until 2005 there was no support in the 802.11 standard priority data and the use of multimedia services in these networks is problematic. Thesis deals with the standard IEEE 802.11 standard and quality of service support including IEEE 802.11e. They discussed methods of access to transmission medium, differences in the MAC sublayer, the reader issues in the transmission of priority data and the requirements for these data. In Opnet Modeler was created wireless network with access points and stations on which they are carried out simulations at different strain of transmitted data. It studied the difference in the use of DCF and EDCF method, used in the network with QoS support. In particular, it examined the behavior of priority voice and video data in both networks. The focus is on key parameters such as throughput, dropping data, packet loss, delay, jitter and the size of broadcasting front. The measured data are analyzed, and differences in the network without the support and promoting the quality of services are compared and evaluated. Part of this work is the role of laboratory in the Opnet Modeler.

Nowadays every wireless radio-communication services encompass huge type of technology used for transfer video, voice or data. Wireless communication is the most expanded branch and many companies are using this technology because of low cost and simply management. The biggest advantage is easy connection to shared wireless medium and allows users of network to move around whole covered area. The most expanded types of wireless networks are called Wireless LAN (WLAN). With rising number of WLANs is rising chance to attack shared wireless medium by hacker and many sensitive information can be stolen or modified. To avoid this chance was created the first security protocol used in WLAN called WEP. Its goal was protect data transmitted trough WLAN as strong as were protected in wired networks. Unfortunately WEP was hiding a big weakness which can be used in a crack of WLAN in a minute with the aid of special software. Example of this kid of software can be Airsnort constructed to monitor shared medium and captured every packet transferred trough this medium. Based on statistical method Airsnort can obtain hidden password in a few minutes. The second type of this software can be Aircrack-ng, which can crack hidden password without any user connected to WLAN. Aircrack-ng uses active techniques to generate network load and can obtain password more effectively and faster. The result of both cases was successful and protection of WLAN was completely cracked. Later was created new security protocol called WPA, which had to fix the cryptography weakness of previous WEP. WPA was only temporary security protocol, during standard 802.11 was developing which had to offer highest security and integrity protection of transferred data trough WLAN. For this reasons was created new version of WPA called WPA2 which satisfy requirements of standard 802.11i. Both protocols WPA/WPA2 contain weakness, which can crash security of WLAN. This crack is based on authentication PSK. Attacker during authentication is using information from four-way handshake between user of WLAN and access point. Based on this information attacker can crack password with the aid of password list attack which took approximately 30 minutes. Based on previous result is important to chose strong password contains alphanumeric string or special strings with satisfy length.

This master´s thesis is about 802.11 standard security techniques and their features. Particular types of this standard and its features are shown in the introduction. Wireless network security cypher alghoritm types, their features, weaknesses and principles of functions are closely described in next few chapters. Realized attacks on these security alghoritms with their principles are described and shown in the practical part of thesis. One chapter is about effectivity, accessibility and practicability valorization of these attacks in practice.

This thesis describes the problems of access networks and their existing types. It discusses the important parameters for multimedia services. It considers the possibility of using various networks at the localities. It presents modern multimedia services and their requirements for access networks. Next step describes the possible use of QoS to optimize access networks used for multimedia services. Multimedia services to different types of networks and limits which these types of networks have, are simulated in the program Opnet Modeler. Measurements of values important for securing quality of services are implemented at selected real access networks. In conclusion, the results of simulations and measurements are subjected to comparative analysis.