Abstract Wireless local area networks (WLANs) have been rapidly developed in recent years. It is used for various applications. VoWLAN, which transmits VoIP data over WLANs, shows its amazing attraction and constitutes one of the most flourishing applications nowadays in WLANs. One of Wireless Local Area Networks (WLAN) main drawbacks, when compared to wired networks, is that WLANs are less predictable and efficient. Wireless physical medium is harder to be controlled than physical wire. WLAN medium is also unlicensed, and thus susceptible to interferences produced by other devices. Therefore, great effort is being done in order to obtain Quality of Service (QoS) in real-time voice communications using WLANs. This topic has opened plenty of new research lines to upgrade current WLAN standards. In this thesis, a study is carried out for the behavior of new Medium Access Control (MAC) protocols defined in IEEE 802.11e draft standard Enhanced Distributed coordination function EDCF as well as for its subsequent modified versions. The Adaptive Enhanced Distributed coordination function AEDCF, designed to support QoS when providing voice communication services between stations in WLAN. Also presents experimental results obtained from simulations, and compare our results with simulations made using IEEE 802.11 standard MAC. The simulation work was done using NS-2 simulator, with the addition of specific modules for 802.11e. A performance comparison is carried out between the modified MAC scheme and IEEE standard MAC scheme, using Experimental simulation models. It is found that the adaptive technique method not only increases the medium utilization ratio and lowers the collision rate by more than 50%, but also enhances vii the overall throughput by around 20% compared with the basic IEEE 802.11DCF technique.
حسين ابراهيم ازويه (2010)

The introduction of new services with different bandwidth requirements, e.g., data and multimedia, to cellular mobile radio networks makes many of the traditional mechanisms unusable or less efficient. The call admission control and the handover handling are the most sensitive issues to this extension. The performance of all services including the traditional voice and the new services can be dramatically effected if no appropriate schemes are used. In this research work, a new call admission and handover handling schemes for a cellular mobile network that offers two service types: voice and data is proposed. The data connections are assumed to be transmitted at different data rates, which are an integer multiple to that of one traffic channels, which are full speed(Cd1) & reduced peed(Cd2). In order to reduce the handover failure probability of data connections, the data mobile terminals (MT) are assumed to have the capability of transmitting at two different data rates. If the handover request can not be satisfied by the base station of the destination cell due to unavailable free traffic channels, the data mobile terminals tries with a lower data rate. The handover fails if the network is incapable on providing the minimum data rate at which the mobile terminal can transmit. The reduced data connection or data rate can be speeded up to full data rate or full speed as soon as enough bandwidth is available. The effect of different traffic and configuration parameters on the performance of the different models for two cell model with equal input traffic intensity, two cell model with different input traffic intensity, and two cell model with equal input traffic intensity considering the congestion rate for the highway model are studied as the models of this research. These models are built using MOSEL language (Modeling Specification and Evaluation Language). The results of investigating the mentioned models showed the effect of the handover, and speed of data on these different models.
W. ABUGHRES(1-2000)

Abstract Ad-hoc networking is a concept in computer communications, which means that users wanting to communicate with each other form a temporary network, without any form of centralized administration. Each node participating in the network acts both as host and a router and must therefore be willing to forward packets for other nodes.In a multi-hop wireless packet network, a packet traverses more than one wireless link in traveling from its source to its destination. Such wireless networks have received considerable attention recently in the context of ad hoc networks. Ad-Hoc networks are self-organizing multi-hop wireless networks where not all links along the path of a packet can be activated simultaneously. Hence the performance of a higher level mechanism, such as congestion window or Transport Layer protocol (TCP) will depend crucially on how the links are scheduled for transmission. In multiple access networks, such as the IEEE802.11 wireless LAN, the scheduling of transmissions is done by the medium access control (MAC) protocol. This transmission scheduling is completely unaware of the needs of the TCP congestion window protocol. This thesis is concerned with the poor interaction between the TCP adaptive window protocol, the IEEE 802.11 MAC protocol, and the IEEE 802.11 Ad-Hoc routing protocol. Our thesis follow on the work done by the researchers K. Nahm and C. Kuo in the paper entitled “TCP over 802.11 Multihop networks issues and Performance Enhancement” [1]. Our contributions are two-fold. First we have repeated and confirmed the simulation results reported by K.Nahm and C.Kuo using NS-2 network simulator. Second we have introduced a simple modification in the 802.11 DSR routing protocol which reduces the unnecessary VI reroutings triggered by MAC packet collisions and enforces the TCP to enter the fast retransmit / fast recovery phase to quickly recover the packet loses. This modification has been simulated using NS-2 network simulator and from the results we have found that it provides a substantial improvement in TCP performance in the situations that we have considered in the simulation models
يحي الشارف المبروك (2009)