Wireless has its advantage over wired side particularly in supporting its users with mobility. The IEEE 802.11 Wireless Local Area Network (WLAN) popularity has far exceeded its expectations, by the rapid growth in its deployments. Beside supporting mobility, this technology can provide high data rate with a lower cost when compared to other technologies from the same category. However, the increasing demands on supporting the QoS for the emerging multimedia streaming applications while using this technology has exposed the need to reconsider the specifications of the 802.11 standard and its variations (a, b, and g), specially for the horizontal handoff when Mobile Hosts (MHs) roam in between the Basic Service Set (BSS) cells for the reason that the latency results from performing this procedure observed and measured to be much higher than the strict delay constraints recommended for multimedia streaming applications, which also known as delay sensitive applications Like VoIP and IPTV.
In this thesis, the conventional 802.11 handoff procedure and its related work have been comparatively studied to characterize the factors affecting the total handoff delay. In addition, an advanced handoff mechanism is presented. The proposed mechanism is mainly to assign a threshold value for terminating the handoff procedure which can reduce the total handoff delay and energy consumption by minimizing number of channels scanned. Furthermore, we developed the proposed mechanism for more QoS considerations by applying the cross layer communication concept, to dynamically deliver the imperative Application Layer's information to the MAC Layer. The performances of the proposed handoff mechanism and its enhanced version are evaluated by simulations. Simulation results show that both of the proposed mechanisms outperform the conventional handoff procedure by reducing the handoff latency to a value acceptable for delay sensitive applications, and enhancing the MH's power consumption.
Besides its apparent benefits in supporting QoS for WLAN side, the proposed handoff mechanism can be shown as a possible solution to reduce loss probability of high priority class packets in a converged WLAN over Optical Burst Switching (OBS) systems. Here, we present guidelines for designing such system by proposing a synchronization technique to be performed between horizontal handoff of the WLAN side, and the process of dissolving the bursts into packets in OBS systems which we consider here as vertical handoff. Along with synchronization technique, a Dynamic Dropping Policy (DDP) is proposed, which has the major role in reducing the loss probability of high class packets.
