Horizontal Handoffs within WLANs : A detailed analysis and measurement concerning voice like traffic

Abstract: 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.