Abstract
This thesis begins by addressing the problems and challenges faced in a multimedia, ATM compatible. Wireless LAN environment. A brief overview of the ATM will also be presented. An extension to the conventional wireless (cellular) architecture, which takes advantage of the ATM characteristics, is considered. The needs of the applications that will use such a network along with the services this network is expected to offer, are discussed. The existing wireless protocols (both in the wireless LANs and in the cellular architecture) are presented. The differences among the MAC schemes and discussion on the criteria they must satisfy to support ATM are brought up. Finally, the most promising MAC schemes are discussed in further details. Furthermore, the introduction of terminal and user mobility in an ATM LAN causes the need for modification of the existing network functions. There are new problems, associated with the mobile stations that must be addressed, such as location management, paging, registration, authentication and network security and handover implementation. Furthermore, existing functions of the fixed ATM, such as Connection Admission Control and traffic shaping need to be extended to support the requested QoS in the wireless environment. The next part of the report discusses the different types of handover mechanisms and presents possible extensions of the UNI and PNNI that support the exchange of handover messages. The concept of the Mobile Agent (MA) is also introduced and its use in the extended UNI and PNNI for handover execution, registration and location management purposes is presented. Finally, a further extension of the PNNI protocol, which could be used among the different MAs, in order to support portability across different private ATM LANs, is being discussed. Without a doubt there will be a requirement for interworking between ATM and the already established wireless networks (e.g. HIPERLAN, DECT, IEEE 802.). The use of ATM as a wireless network backbone is particularly advantageous in microcell and/or integrated voice/data scenarios, and is cost-competitive with other possible implementations. Taking that into consideration, the transmission of ATM cells over a WLAN, based on the IEEE 802.11 MAC layer has been investigated. Initially, the IEEE 802.11 MAC layer and its model (developed in BONeS software package), are being discussed. The simulation results show the existence of upper bound delays for delay sensitive applications, such as voice and video, which are not affected by the traffic load on the network. Moreover, a power saving addition to a Dynamic Time Division Multiple Access (D-TDMA) MAC protocol, suitable for ATM cell transmission, discussed in [APOS95], will be proposed. A short presentation of the MAC protocol and the proposed power saving algorithm will follow. The trade-off between the power saving gain and the size of the buffer in the Access Point (AP) are shown for different kinds of services. Finally (based on Markov chains), the calculation of the call blocking and dropping probabilities for different services in a radio environment will be addressed. This method considers both the different QoS requirements for each service and the load on the network. The results obtained with the analysis are being compared to the ones obtained from simulations.