Mobility support is one of the most challenging issues in IEEE 802.11 networks. In the proactive neighbor caching (PNC) scheme, when a mobile host is connected to an access point (AP), its context (e.g. security association or QoS information) is propagated in advance to all of the AP’s neighbors to reduce handoff processing time. In this paper, we propose

With the proliferation of mobile wireless devices such as smartphones and tablets that are used in a wide range of locations and movement conditions, it has become important for wireless protocols to adapt to different settings over short periods of time. Network protocols that perform well in static settings where channel conditions are relatively stable tend to perform poorly in mobile settings where channel conditions change rapidly, and vice versa. To adapt to the conditions under which communication is occurring, we propose the use of external sensor hints to augment network protocols. Commodity smartphones and tablet devices come equipped with a variety of sensors, including GPS, accelerometers, magnetic compasses, and gyroscopes, which can provide hints about the device’s mobility state and its operating environment. We present a wireless protocol architecture that integrates sensor hints in adaptation algorithms. We validate the idea and architecture by implementing and evaluating sensor-augmented wireless protocols for bit rate adaptation, access point association, neighbor maintenance in mobile mesh networks, and path selection in vehicular networks. 1

In recent years, many protocols have been developed to support user mobility in wireless networks, e.g. Mobile IP suite of protocols designed to support IP routing to mobile nodes. However, support for truly seamless mobility requires more than just routing: every service associated with the mobile user needs to be transferred smoothly to the new access network. In this paper, we will concentrate on the problem of transferring service state (context) at both the link and the IP layers. We propose a method to estimate the best moment in time for transferring context information associated with the mobile user. As one of key issues in the proactive context transfer scheme is accuracy of handover prediction, we suggest and describe a new concept of Forced Handover that can provide very low handover latency. The simulation results and the following discussions show that our scheme is helpful in ensuring seamless mobility, while keeping the number of unnecessary handovers resulting from the proactive nature of the scheme at a controllable level. I.

With the growth of IEEE 802.11-based wireless LANs, VoIP and similar applications are now commonly used over wireless networks. Mobile station performs a handoff whenever it moves out of the range of one access point (AP) and tries to connect to a different one. This takes a few hundred milliseconds, causing interruptions in VoIP sessions. We developed a new handoff procedure which reduces the MAC layer handoff latency, in most cases, to a level where VoIP communication becomes seamless. This new handoff procedure reduces the discovery phase using a selective scanning algorithm and a caching mechanism.

This study first reviews state-of-the-art fast handoff techniques for IEEE 802.11 or Mobile IP networks. Based on that review, topology-aided cross-layer fast handoff designs are proposed for Mobile IP over IEEE 802.11 networks. Time-sensitive applications, such as voice over IP (VoIP), cannot tolerate the long layer-2 plus layer-3 handoff delays that arise in IEEE 802.11/Mobile IP environments. Cross-layer designs are increasingly adopted to shorten the handoff latency time. Handoff-related layer-2 triggers may reduce the delay between layer-2 handoff completion and the associated layer-3 handoff activation. Cross-layer topology information, such as the association between 802.11 access points and Mobile IP mobility agents, together with layer-2 triggers, can be utilized by a mobile node to start layer-3 handoff-related activities, such as agent discovery, address configuration, and registration, in parallel with or prior to those of layer-2 handoff. Experimental results indicate that the whole handoff delay can meet the delay requirement of VoIP applications when layer-3 handoff activities occur prior to layer-2 handoffs. 1.

Abstract — A research topic that is becoming increasingly popular is that of on-board mobile communication, where users on a vehicle are connected to a local network that attaches to the Internet via a mobile router and a wireless link. However, wireless data transmission is less efficient, prone to error and unreliable in a mobile environment. There is a need to make use of multiple access links simultaneously (so-called multihoming), to improve the aggregate bandwidth and the overall service availability on a mobile network. In this paper, we introduce a novel on-board Multihoming Agent for supporting the future on-board multihomed mobile routers. The Multihoming Agent can intelligently stripe user traffics into multiple active WAN interfaces based on the policy in use and the real-time network status and automatically shift user traffics from unavailable links to available ones. We show that by properly deploying the policies defined in the Policy Database and continuously collecting network status, a user can run intelligent load distribution algorithms on top of the mobile router to improve network performance and reliability via our Multihoming Agent. I.

In this paper, we focus on one of the most critical security issues authentication. Authentication within wireless networks is reviewed. Wi-Fi security weaknesses are illustrated. These drawbacks involve the necessity of designing a new generation of secure wireless systems. In fact, selfcontrol, flexibility, adaptability, autonomy and distribution are the main features to be addressed in a suitable architecture that fulfills modern requirements. In this context, we propose an incremental approach to the final solution which features secure access control with roaming. An acceptable management and installation price are expected. Intermediate steps are discussed in detail. Security goals and system architecture guidelines are outlined.

Abstract-- With the increasing popularity of powerful handheld / mobile computing devices and ubiquitous availability of wireless connectivity, protocols that support mobility are becoming increasingly important. It is critically important to explore and understand the design space, so that appropriate mechanisms are incorporated into the design to provide the required performance under varied environments and services provided by the lower layers. The mechanisms incorporated into the design may interact in subtle ways with the mechanisms of the higher layer to produce unintended effects. In this paper, we study how the different mechanisms of the lower layers (IP and MAC) that support mobility affect the performance of Transmission Control Protocol (TCP). We use the building block framework to capture and study the wide variety in the IP layer handover optimization mechanisms. We use detailed 802.11 models to study the effect of MAC layer mobility support on TCP. We show by simulation how different mechanisms affect TCP differently in different scenarios. We also show results that very counter intuitive, like buffering packets does not always improve TCP throughput and TCP-Tahoe performs better than its more sophisticated counterparts.

Not only the proliferation of 802.11, but also the capability to determine the position of mobile devices make 802.11 highly appealing for many application areas. Typically, a mobile device that wants to know its position regularly performs active or passive scans to obtain the signal strength measurements of neighboring access points. Active and passive scanning are survey techniques originally intended to be performed once in a while to learn about the presence and signal reception quality of access points within communication range. Based on this survey the best suitable access point is selected as the gateway to the wired network. However, so far, no investigations are known to have been launched into how regular scanning affects concurrent data transmissions from an end-user point of view. In this paper, we explore how common data communication is affected while actively or passively scanning at the same time. We found that with an active scanning interval of less than 2 seconds the network conditions such as throughput and round trip delay are insufficient for interactive applications. The same is true for passive scanning if a scanning interval of less than 7 seconds is chosen. Furthermore, we present a novel scan scheme called Monitor Sniffing to reduce client service disruptions. Monitor Sniffing exploits the fact that 802.11 operates on overlapping channels by overhearing the wireless interface. We have implemented our Monitor Sniffing algorithm using commodity 802.11g hardware, and we demonstrate that it is faster than active and passive scanning and does not disturb concurrent data communication. Finally, our approach only requires software modifications on the client side, making the adoption process quite easy. 1

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