MeshScan: a Fast and Efficient Handoff Scheme for IEEE 802.11 Wireless Mesh Networks

As a next generation network solution, Wireless Mesh Networks (WMN) provides fast Internet access to a large area, which is from university campus to city scale. In order to provide an uninterrupted Internet experience to a mobile client, a process called handoff is required to maintain the network connection from one Mesh Node (MN) to another MN. Ideally, handoff should be completely transparent to mobile users. A critical application like VoIP will require a handoff capability that transfers a call from one mesh node (MN) to another in less than 50 msec. However the current IEEE 802.11 standards do not address the handoff well. Studies have revealed that standard handoff on IEEE 802.11 WLANs incurs a latency of the order of hundreds of milliseconds to several seconds. Moreover, the discovery step in the handoff process accounts for more than 99% of this latency. The study addresses the latency in the discovery step by introducing an efficient and powerful client-side scan technique called MeshScan which replaces the discovery step with a unicast scan that transmits Authentication Request frames to potential MNs. A prototype of MeshScan has been developed based on the MadWifi WLAN driver on Linux operating systems. The feasibility of MeshScan to support fast handoff in WMNs has been demonstrated through extensive computer simulations and experiments under same given conditions. The results from the simulations and experiments show that the latency associated with handoff can be reduced from seconds to a few milliseconds by using the MeshScan technique. Furthermore, it is shown that MeshScan can continue to function effectively even under heavy traffic loads

Multichannel Virtual Access Points for Seamless Handoffs in IEEE 802.11 Wireless Networks

Session: Handoff and Mobility Management 2International audienceWithin IEEE 802.11 Wireless Local Area Networks (WLANs), client stations can move freely, but because of the short range of their Access Points (APs), they usually need to reassociate with different APs to continue to communicate. When changing APs, a client station starts a process known as a handoff that can take up to 2 seconds, which is too long for real-time applications such as Voice over IP (VoIP). Various solutions have been proposed to change or improve the client behaviour when doing a handoff. Previously, we proposed the idea of Virtual Access Points (VAP) implemented on APs in which a client station changes APs without disrupting its current communication. Based on this new concept, we have developed a solution called Multichannel Virtual Access Points (mVAP) to take advantage of APs operating on multiple channels. We have implemented mVAP using PACMAP, a tool for packet manipulation, and evaluated its performance. Our results show that mVAP is a new efficient technique for seamless handoffs without performance degradation

Improving Ieee 802.11 Wlan Handoff Latency by Access Point-Based Modification

IEEE 802.11 WLAN provides multimedia services like live telecast, video streaming, video conferencing, Voice over IP (VoIP) to its users. For deployment of these fast real time services, it needs stringent Quality of service (QoS) requirement such as delay time less than 150ms for VoIP, and packet loss rate of 1%. The mobility service for users come with cost of handoff process required when mobile stations get connected from 1 Access point (AP) to another for continuous service. In existing 802.11 IEEE handoff procedure, the scanning phase can exceed duration of 200ms and packet loss can exceed 10%. Thus, proposed methodology focuses on achieving reduced overall handoff latency by implementing handoff delay duration less than 150ms which is the need for seamless service in IEEE 802.11 WLAN

An Adaptive Multimedia-Oriented Handoff Scheme for IEEE 802.11 WLANs

Previous studies have shown that the actual handoff schemes employed in the IEEE 802.11 Wireless LANs (WLANs) do not meet the strict delay constraints placed by many multimedia applications like Voice over IP. Both the active and the passive supported scan modes in the standard handoff procedure have important delay that affects the Quality of Service (QoS) required by the real-time communications over 802.11 networks. In addition, the problem is further compounded by the fact that limited coverage areas of Access Points (APs) occupied in 802.11 infrastructure WLANs create frequent handoffs. We propose a new optimized and fast handoff scheme that decrease both handoff latency and occurrence by performing a seamless prevent scan process and an effective next-AP selection. Through simulations and performance evaluation, we show the effectiveness of the new adaptive handoff that reduces the process latency and adds new context-based parameters. The Results illustrate a QoS delay-respect required by applications and an optimized AP-choice that eliminates handoff events that are not beneficial.Comment: 20 pages, 14 figures, 4 table

Application of the DQCA protocol to the optimization of wireless communications systems in cellular environments

This final career thesis (Master thesis) is a contribution on the enhancement of wireless communications, specifically WLAN multi-cell systems based on the IEEE 802.11 standard. The objectives were to propose and study different Cross-Layer AP selection mechanisms that include single, dual and multiple metric based criteria using PHY-MAC interactions. These mechanisms are designed in order to improve system efficiency through the increase of the utilization of the available transmission resources. The key idea of these mechanisms is to make use of certain PHY and MAC parameters, other than the traditional RSSI measurements, in order to optimize the association to the best AP, specially focusing on the innovative use of MAC level state metrics. In this regard, of special interest is the inclusion of MAC level AP traffic load estimations within these association decisions. All the proposals are based on the use of a high-performance MAC protocol called DQCA (Distributed Queueing Collision Avoidance), which is specially fitted to include the proposed techniques. Computer simulations have been carried out to evaluate and quantify the benefits of the proposed mechanisms and techniques in representative scenarios. Moreover, a completely new handoff procedure has been designed for the DQCA muti-cell operation. This handoff process allows implementing each of the proposed AP selection mechanisms. Furthermore, the interaction between a Cross-Layer scheduling technique at the MAC level and two proposed AP selection mechanisms has also been studied. The performance of these techniques has also been assessed by means of computer simulations. The analysis of the obtained results show that the proposed mechanisms perform differently under the considered scenarios. However, the main conclusion that can be drawn is that AP selection mechanisms that are based on joint multiple metrics considerations (SNR, AP load, delay, etc.) perform significantly better than those that use only single or dual metric based mechanisms. After the study, we can conclude that the proposed techniques and mechanisms provide significant efficiency enhancements for DQCA-based WLAN multi-cell systems so that all of them may be taken into account in future wireless networks

Behavior-Based Mobility Prediction for Seamless Handoffs in Mobile Wireless Networks

The field of wireless networking has received unprecedented attention from the research community during the last decade due to its great potential to create new horizons for communicating beyond the Internet. Wireless LANs (WLANs) based on the IEEE 802.11 standard have become prevalent in public as well as residential areas, and their importance as an enabling technology will continue to grow for future pervasive computing applications. However, as their scale and complexity continue to grow, reducing handoff latency is particularly important. This paper presents the Behavior-based Mobility Prediction scheme to eliminate the scanning overhead incurred in IEEE 802.11 networks. This is achieved by considering not only location information but also group, time-of-day, and duration characteristics of mobile users. This captures short-term and periodic behavior of mobile users to provide accurate next-cell predictions. Our simulation study of a campus network and a municipal wireless network shows that the proposed method improves the next-cell prediction accuracy by 23~43% compared to location-only based schemes and reduces the average handoff delay down to 24~25 ms

Behavior-Based Mobility Prediction for Seamless Handoffs in Mobile Wireless Networks

The field of wireless networking has received unprecedented attention from the research community during the last decade due to its great potential to create new horizons for communicating beyond the Internet. Wireless LANs (WLANs) based on the IEEE 802.11 standard have become prevalent in public as well as residential areas, and their importance as an enabling technology will continue to grow for future pervasive computing applications. However, as their scale and complexity continue to grow, reducing handoff latency is particularly important. This paper presents the Behavior-based Mobility Prediction scheme to eliminate the scanning overhead incurred in IEEE 802.11 networks. This is achieved by considering not only location information but also group, time-of-day, and duration characteristics of mobile users. This captures short-term and periodic behavior of mobile users to provide accurate next-cell predictions. Our simulation study of a campus network and a municipal wireless network shows that the proposed method improves the next-cell prediction accuracy by 23~43% compared to location-only based schemes and reduces the average handoff delay down to 24~25 ms