The diploma thesis is focused on exploring the possibility of VoIP service in a wireless network of University of Economics, Prague. This thesis describes the basic principles of VoIP and related wireless technologies necessary for its quality and stable operation. Subsequently, different configurations of wireless network and end clients are tested and compared, including its impact on ordinary users, in a laboratory environment with idle and fully utilized frequency band. Finally, a roaming operation with the use of several advanced 802.11 standards is tested in the real environment of the Old building in Žižkov. In conclusion, the ideal settings for all telecommunication devices are recommended in order to maximize the quality of VoIP operation and to minimize the negative impact on ordinary users.

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.

Communication is often limited in a disaster area and other emergency situations where no infrastructure exists or existing infrastructure has been destroyed. This makes its difficult for relief workers in the field to communicate with one another and with their home head office. Ericsson Response has developed a Wireless LAN in Disaster and Emergency Response (WIDER) solution. WIDER is based on broadband Wireless LAN internetworking to satellite and GSMnetworks. The WIDER solution has identified ways for organizations to share their communication infrastructure, and information in a secure and cost effective manner during an emergency response operation. Data over WIDER needs to be secured to prevent from unauthorized access to sensitive information of relief organizations. VoIP calls should be protected against eavesdropping. The thesis investigated how to enhance security solution in WIDER and implement a secure VoIP client. Measurements of the performance of WIDER and the total delay of VoIP over satellite were used to estimate the capability of WIDER before deployment in the field. / Kommunikation är ofta begränsad i katastrofområden och andra nödsituationer där infrastruktur saknas eller har blivit förstörd. Det gör det svårt för fältarbetande personal att kommunicera, både med varandra och centraliserade kontor. Ericsson Response har utvecklat en lösning kallad "Wireless LAN in Disaster and Emergency Response" (WIDER). WIDER använder trådlöst LAN och är en bredbandsbaserad internetteknik mot satelit- och GSM-nätverk. WIDER har identifierat lösningar för organisationer att dela deras infrastruktur för kommunikation och information på ett säkert och kostnatseffektivt sätt vid nödsituationer. Informationen som skickas via WIDER behöver bli skyddad för att förhindra oaktorisierad tillgång till känslig information. VoIP förhindrar obehöriga att avlyssna trafiken. Examensarbetet har undersökt den utökade säkerhetslösningen för WIDER och har implementerat en säker VoIP-klient. Mätningar av prestanda hos WIDER och den fördröjning som sker med VoIP över satelitlänk användes för att estimera WIDERs kapacitet innan systemet används i fält.

IEEE 802.11 based Wireless Local Area Networks (WLANs) in addition to being used as access networks for providing traditional data services, are now also being used as access networks for providing realtime services such as VoIP and multimedia streaming. These realtime services are sensitive to latency, hence requiring seamless or low delay service from the lower layers throughout an ongoing session. The IEEE 802.11 standard does not define any technique or algorithm to provide seamless connectivity during the process of handoff, hence it does not require 802.11 based WLANs to provide the same. Thus, it is typical that there is a latency of 500 milliseconds to 1000 milliseconds during the handoff, before the mobile station can connect and receive data from the new access point (AP). However, many realtime services can not tolerate this much latency. The problem of handoff latency is further aggravated when WLANs are secured using IEEE 802.11i standard and when Authentication, Authorization & Accounting (AAA) services are involved in controlling network access to 802.11 based WLANs. This thesis will address the entire handoff process and examine the latency -- especially regarding AAA services. Different techniques and suggestions will be presented and analyzed closely at different layers and based on the results, an appropriate/efficient algorithm is suggested which will reduce this handoff latency, such that that seamless handoff can be achieved and realtime services can be provided over 802.11i enabled IEEE 802.11 WLANs. / Wireless Local Area Network (WLAN), baserat på IEEE 802.11 har traditionellt nyttjats som som accessnät för vanliga datatjänster. Ett allt vanligare användningsområde har blivit att nyttja samma nät för realtidstjänster som Voice over IP (VoIP) och mutimedia. Realtidstjänster är känsliga för fördröjningar. Fördröjningar som bland annat kan erhållas från de lägre nivåerna i OSI-stacken. IEEE 802.11-standarden definierar ingen teknik eller algoritm för att säkerställa avbrottsfri/fördröjningsfri transmission av data vid handoff och följdaktligen så kan man idag inte luta sig mot denna standard för att erhålla denna funktionalitet. Med nyttjande av befintlig IEEE 802.11 standarder erhålls fördröjningar på mellan 0,5 till 1 sekunder. Detta är naturligtvis inte acceptablet för många realtid och realtidsliknande tjänster. Problemet vid handoff accentueras ytterliggare om kravs ställs på AAA-tjänster för att säkerställa säkerheten i ett IEEE 802.11-baserat WLAN. Denna uppsats adresserar hela handoffprocessen med tillhörande fördröjningar – speciellt med hänsyn till AAA-tjänsterna. Olika tekninker och förslag presenteras och analyseras på olika nivåer. Baserat på erhållna resultat föreslås en algoritm för att reducera tidsåtgång vid handoff, så att realtidsliknande tjänster erhålls, utan störande fördröjningar, vid nyttjande av 802.11i.

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