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In this paper, we present a new communication protocol for low-cost Internet-of-Things (IoT) devices that need to gather and transmit sensor data and receive remote commands. Taking into account that an IoT-network may employ different communication technologies, we define several important protocol features such as data encryption, integrity checking, sender authentication and data retransmission in case of packet delivery failures. We describe our approach to implementing each of the protocol features as part of our HybridNET system for industrial device control and communication. The hardware base includes cheap 32-bit microcontrollers, radio connectivity (SX1276 and others) and wired connectivity (mainly RS485 and Ethernet). We also describe the protocol packet structure in detail as well as our implementation for routing packets in larger IoT-networks. The experimental results are very promising and show that our protocol performs very well and delivers very good performance and reliability.

For single-owner multi-user wireless sensor networks, there is the demand to implement the user privacy-preserving access control protocol in WSNs. Firstly, we propose a new access control protocol based on an efficient attribute-based signature. In the protocol, users need to pay for query, and the protocol achieves fine-grained access control and privacy protection. Then, the protocol is analyzed in detail. Finally, the comparison of protocols indicates that our scheme is more efficient. Our scheme not only protects the privacy of users and achieves fine-grained access control, but also provides the query command validation with low overhead. The scheme can better satisfy the access control requirements of wireless sensor networks.

Full-duplex wireless information and power transfer allows the implementation of wireless sensor networks without batteries. In a full-duplex wireless network, an access point and sensor nodes transmit information and power signals simultaneously. However, this simultaneous transmission leads to a collision problem. To solve this collision problem, we propose a media access control (MAC) protocol, namely the Full-Duplex Simultaneous Wireless Information and Power Transfer Medium Access Control (FD-SWIPT MAC) protocol, for full-duplex wireless information and power transfer. The evaluation results show that the proposed FD-SWIPT MAC protocol outperforms other MAC protocols.

When the same content is simultaneously downloaded by several terminals with unicast in a wireless LAN, the bandwidth must be divided among the terminals and download speed is reduced. With using broadcast nature of wireless media, we propose an efficient method that can achieve reliable content distribution by using overheard TCP flows of a specific content going to other terminals in a wireless LAN. In the proposed method a content is divided into pieces and the server distributes them according to the download status of the receivers in application level. To accelerate downloading, we propose a method for selecting the piece and the terminal for transmission taking the effect of network coding for efficient overhearing. We developed a testbed and confirmed that the proposed scheduling accelerates the download speed even where the communication speed of each terminal is different.

This paper introduces a novel wireless collaborated hybrid data center architecture called RF-HYBRID that could optimize the effect of wireless transmission while reduce the complexity of wired network. RF-HYBRID improves throughput and packet delivery latency through flexible wireless detours and shortcuts, with a comprehensive routing and congestion control method.

The rapid advancements in wireless communication technologies and micro-electronics systems have fostered the development of small and intelligent micro-components that incorporate sensing devices and wireless communications into a single miniature circuit that are wearable or implementable inside the human body for the purpose of medical and healthcare applications. These components when deployed are mainly known as WBANs for Wireless Body Area Networks. One of the main issues in such networks is the medium access techniques mainly for those data which could be urgent. The design of a medium access control protocol for a WBAN is a challenge due to the characteristics of wireless channel, the diversity of traffic, access latency and the need for minimization of energy consumption. Based on the integrated super frame structure of IEEE 802.15.4 and IEEE 802.15.6, an hybrid medium access control protocol named Priority MAC (PMAC) is proposed in this paper. In PMAC protocol, data channels are separated from control channels and the priority is given to the life critical traffic (emergency traffic). Furthermore, a sleep mode is used in order to save energy of the wearable wireless sensors and hence increase their lifetime.

IEEE 802.11ac is an upcoming standard for wireless LAN physical layer and MAC layer for very high throughput (VHT) communication with targeted throughput greater than 1 Gbps [1] below 6 GHz band. The IEEE 802.11ac (also termed as VHT wireless LAN) physical layer is based on orthogonal frequency division multiplexing (OFDM) modulation and signal processing with multiple antennas at transmitter and receiver (MIMO). A device compliant to IEEE 802.11ac standard should be backward compatible to wireless LAN standards IEEE 802.11a and IEEE 802.11n. The VHT Physical layer supports legacy frame format, high throughput (HT) mixed frame format, HT green-field frame format and VHT mixed format [2, 3]. The VHT wireless LAN receiver has to synchronize for any of these frame formats. The OFDM modulation is sensitive to timing synchronization in multipath fading channel. The cyclic shift diversity (CSD) used in VHT wireless LAN introduces pseudo multipath at the receiver and causes error in the symbol boundary estimate. Hence, there is a need for a robust and adaptive time synchronization that suits for all frame formats in VHT wireless LAN. Without the accurate time synchronization, there will be inter symbol interference (ISI) and inter carrier interference (ICI) in the demodulated data, and cause many bit errors in the decoded data. In this paper, we propose a robust and adaptive timing synchronization technique for VHT Wireless LAN device compliant to IEEE 802.11ac standard. We will show the need for the adaptive window length in time synchronization theoretically. The proposed method works well for all frame formats and BW options of the IEEE 802.11ac standard. We will give simulation results to show the usefulness of the method.

IEEE 802.11 wireless local area network (WLAN) has become popular and has been providing excellent solution for wireless networking. With the popularity of WLAN and Voice over the Internet (VoIP) protocol, it is very essential to measure the performance of the VoIP over WLAN. The main goal of this paper is to compare the performance of the Voice over IP protocol in both LAN (802.3) and WLAN (802.11). This paper examines how this communication protocol performs in two different network setups and analyzes the results obtained using OPNET modeler. It also examines the optimization of 802.11e for Quality of Service (QoS) using the priorities to provide real-time service for voice over the Internet protocol.

The prospect of establishing wireless local area network (WLAN) has many major issues, one of which happens to be the determination of the best placement of the access points (AP). This problem consists of determining the optimal locations for AP in order to maximize the coverage area with a minimum number of access points. Because there happens to be a large number of possible solutions, this problem is suitable to be tackled with evolutionary techniques, so in this work it has been developed inspired on the well-known Differential Evolution (DE) method. Experimental results have revealed the efficiency of this proposed algorithm.

Data Center Networks (DCNs) suffer from the congestions caused by unbalanced traffic distributions. Nevertheless, it is difficult to address such a challenge with the existent Ethernet-based DCN architecture. Wireless networking has been considered as a viable approach with a high potential to tackle the problem due to its flexibility. This paper presents Wireless Link Scheduling for Data Center Networks (WLS-DCN) to provide a feasible wireless DCN. More specifically, we propose a wireless DCN architecture as well as a scheduling mechanism. In our wireless scheduling, two different optimization objectives are considered, with one targeting the unbalanced traffic distribution and one maximizing the total network utility, under the constraints of limited wireless resources and co-channel interference. We propose two heuristics for the two problems and carry out extensive simulation study to validate the performance of our design. Our results demonstrate that WLSDCN can significantly improve the performance of DCN.

The increasing use of wireless technologies in enterprise networks demands strong security management and policy enforcement mechanisms. The conventional security management frameworks used in wired LAN do not suit in wireless domain due to dynamic topology and mobility of hosts. The enforcement of organizational security policies in wireless LAN requires appropriate access control models as well as correct distribution of access control rules in the network access points. In this paper, we propose a WLAN security management framework supported by a spatio-temporal RBAC (STRBAC) model. The concept of mobile IP has been used to ensure a fixed layer 3 address of a mobile host. Each wireless policy zone consists of a Policy Zone Controller that coordinates with a dedicated Local Role Server to extract the low level access configurations corresponding to the zone access routers. The system can be mapped into a reconfigurable hardware to exploit the parallelism in computing. We also propose a formal STRBAC model to represent the global security policies formally and a SAT based decision procedure to verify the access configurations

Cross-layer design has proven to be a promising approach to achieving optimal performance in wireless networks. However, care must be taken when designing cross-layer protocols and frameworks so as to avoid excessive complexity and loss of standardization. In this paper, we propose a cross-layer framework for wireless sensor networks which preserves modularity and clearly defines the inter-layer interactions allowing for ease of standardization and long-term development. This Central-Networked framework consists of the centered physical and centered application models.

We present VPSI, which is a Virtual Protocol Stack Interface for wireless network simulators. VPSI provides two features; 1) a unified programming interface for developing network protocols, and 2) separation of simulator engine and the network protocols. By using VPSI, developers do not need to understand multiple different simulator engines. We implemented and adapted VPSI on existing well-known simulation packages, and we observed that VPSI works well with different wireless network simulators.

This paper presents an automatic planning software tool for indoor wireless networks. As a consequence of increasing number of wireless interface based systems, automation of deployments becomes actually relevant. There are a lot of parameters that influences network performance, so designers have to take them into account. The larger the network is, the more complex its planning results are. Planning determines performance, and getting it manually is not efficient. Mentioned tool automatically looks for an optimal planning solution, in terms of base stations distribution and frequency planning. It consists of analyzing data obtained by means of environment simulation. The user is able to decide the optimization criterion and the algorithm for searching solutions. This tool obtains an optimal solution in a short period of time, and it shows results such as power received at each user spatial point, interference level or traffic load for each station.

The ubiquitous IEEE 802.11 standard exhibits a significant amount of MAC protocol overhead inherent to contention-based random access protocols. To alleviate this overhead and improve protocol performance, a dynamic protocol timing adaptation scheme is proposed whereby the fundamental 802.11 slot time and inter-frame spacing are reduced based on techniques that exploit the actual maximum propagation distance within a wireless LAN, in addition to advances in PHY layer technologies that facilitate faster MAC processing and carrier sensing. We show through numerical analysis that the proposed scheme has the theoretical potential to increase system throughput and improve the performance of both current and emerging high-throughput 802.11 wireless LAN standards.

IEEE 802.11 is the most wide-spread standard for wireless LAN due to easy installation and low cost. Most of the WLAN established around the world are working on infrastructure mode. In such mode, there exists an access point (AP) to be a portal to the Internet for wireless users in its coverage. For communications inside a cell, the infrastructure mode is not an efficient way for data transmission. When the number of traffics increases in the WLAN, the contention for accessing the channel makes the system throughput degrade dramatically. How to improve the effectiveness of bandwidth utilization is always one of the most important issues in wireless communications. A better way would be setting up a direct link connection for transmissions between non-hidden stations. In this paper, we refer to Address Resolution Protocol (ARP) and propose a simple new scheme, called ARP-like Direct Link Transmission scheme, to set up direct link connections among non-hidden stations in the same cell. The proposed scheme can effectively improve the overall system throughput and reduce the delay and jitter as shown in the simulation results.

Measuring 802.15.4 reception in three testbeds, we find that most intermediate links are bursty: they shift between poor and good delivery. We present a metric to measure this link burstiness and name it β. We find that link burstiness affects protocol performance and that β can predict the effects. We show that measuring β allows us to reason about how long a protocol should pause after encountering a packet failure to reduce its transmission cost. We find that using β as a guide to setting a single constant in a standard sensor network data collection protocol reduces its average transmission cost by 15%. In addition to data from 802.15.4 testbeds, we examine traces from 802.11b networks and find β has a broader relevance in the wireless domain.

Wireless networks have been widely accepted and deployed in our world nowadays. Consumers are now accustomed to wireless connectivity in their daily life due to the pervasive- ness of the 802.11b/g and wireless LAN standards. Specially, the emergence of the next evolution of Wi-Fi technology known as 802.11n is pushing a new revolution on personal wireless communication. However, in the context of WLAN, although multiple novel wireless access technologies have been proposed and developed to offer high bandwidth and guarantee quality of transmission, some deficiencies still remain due to the original design of WLAN-MAC layer. In particular, the performance anomaly of 802.11 is a serious issue which induces a potentially dramatic reduction of the global bandwidth when one or several mobile nodes downgrade their transmission rates following the signal degradation. In this paper, we study how the use of adaptive erasure code as a replacement of the Auto Rate Feedback mechanism can help to mitigate this performance anomaly issue. Preliminary study shows a global increase of the goodput delivered to mobile hosts attached to an access point.

Developing and evaluating wireless protocols is challenging because it requires flexible network interface hardware, which is not readily available. To reduce the efforts of conducting realistic wireless experiment, we have developed FlexMAC, a wireless protocol development and evaluation platform based on commodity hardware. FlexMAC targets CSMA wireless protocols and allows customization of functions such as backoff, retransmission, and packet timing. In this demo, we will show that FlexMAC is a useful tool for wireless protocol development. We will demonstrate two projects that are developed using FlexMAC, including a software-based 802.11 implementation and an opportunistic relaying protocol in 802.11.

Rogue (unauthorized) wireless access points pose serious security threats to local networks. In this paper, we propose two online algorithms to detect rogue access points using sequential hypothesis tests applied to packet-header data collected passively at a monitoring point. One algorithm requires training sets, while the other does not. Both algorithms extend our earlier TCP ACK-pair technique to differentiate wired and wireless LAN TCP traffic, and exploit the fundamental properties of the 802.11 CSMA/CA MAC protocol and the half duplex nature of wireless channels. Our algorithms make prompt decisions as TCP ACK-pairs are observed, and only incur minimum computation and storage overhead. We have built a system for online rogue-access-point detection using these algorithms and deployed it at a university gateway router. Extensive experiments in various scenarios have demonstrated the excellent performance of our approach: the algorithm that requires training provides rapid detection and is extremely accurate (the detection is mostly within 10 seconds, with very low false positive and false negative ratios); the algorithm that does not require training detects 60%-76% of the wireless hosts without any false positives; both algorithms are light-weight (with computation and storage overhead well within the capability of commodity equipment).

The exponential increase in the deployment of IEEE 802.11-based wireless LAN (WLAN) technology has transformed it into an essential building block of the networking infrastructure of commercial enterprises. How to effectively manage these WLAN networks and stop malicious intruders are the two main barriers for further spread of this technology. At the same time, the enormous economies of scale behind IEEE 802.11-based WLAN products also result in rapid technological advances and astounding pricing efficiencies. In this paper, we describe the design, implementation, and evaluation of a scalable wireless LAN traffic monitoring system called WIreless Network senTRY (Wintry), which provides real-time visibility of the usage of an enterprise's wireless links in a way that is completely transparent to the monitored WLAN networks. Moreover, Wintry is able to leverage low-cost programmable WLAN access points and reduce the total hardware cost to the minimum. A key feature of Wintry is an accurate radio channel busy time estimation algorithm that correctly takes into account both back-off delay and corrupted packets in WLAN traffic load computation without requiring any modification to monitored WLAN devices.

Nintendo DS handheld game units are popular. They are capable of wireless game play using IEEE 802.11 networks. In this paper, we investigated the local Nintendo wireless game traffic and the effect of this game traffic on other wireless users. We analyzed the wireless traffic generated by up to six players for a number of different games. Our analysis showed that the local wireless traffic differed significantly from wide-area wireless traffic for the same games and hardware. The bit rates used made the small game packets appear large to higher speed networks that shared the wireless channel. Also, Nintendo used a point coordination function (PCF) to arbitrate channel access for local games. Ideally, the contention free slots provided by PCF can provide better quality of service for the game traffic. However, this added extra overhead for the coordination traffic, about 98% of polls for Pictochat produced no game data. Also, this PCF coordination packets were unaware of the coexistence of distributed coordination function (DCF) traffic from typical wireless access points; catastrophically interfering with the wireless traffic of other wireless LAN users.

We have built a wireless mesh network testbed, which is tolerant of disaster and aim to resolve a digital divide issue in rural mountain areas. This testbed is located in two areas and has total 22 nodes which are installed on the power poles in these areas. Two areas are connected to a control server at Niigata university with broadband wireless access systems using 5 GHz band via a gate way node at the local-government office, which is located at the center of two areas. Each node has two wireless LAN interfaces with IEEE 802.11b/g and a wireless LAN access point. We measure the throughput and the packet transmission successful ratio of links in our testbed. Moreover, we investigate the technical issues to manage and operate the mesh network in the rural mountain areas.

Nowadays, wireless personal devices, such as cell phones and Personal Data Assistants (PDAs), have gradually taken an important part of our daily lives. With two-factor authentication, the wireless personal devices can be further promoted to more security demanding and mission-critical applications, such as e-commerce, home surveillance, and medical monitoring, etc. Facility access is one of applications that have demonstrated a tremendous market potential for replacing the conventional physical key approach. In this paper, we present a novel keyless facility access control system by using wireless personal devices, where the devices serve as a second authentication factor to assure security. The proposed system is not only cost-efficient, but also capable of mitigating security threats existing in the traditional key control system. Furthermore, the proposed authentication protocol is featured in two different authentication processes for the first time and subsequent accesses by using a one-time authentication mechanism based on one-way hash chain while considering the resource constraints of the wireless personal devices and E-lock. Finally, a role-based access control (RBAC) system is adopted to reduce the complexity of key maintenance.

The low price of commodity wireless LAN cards and access points (APs) has resulted in the rich proliferation of high density WLANs in enterprise, academic environments, and public spaces. In such environments wireless clients have a variety of affiliation options that ultimately determine the quality of service they receive from the network. The state of the art mechanism behind such a decision typically relies on received signal strength, associating clients to that access point (AP) in their neighborhood that features the strongest signal. More intelligent algorithms have been further proposed in the literature. In this work we take a step back and look into the fundamental metrics that determine end user throughput in 802.11 wireless networks. We identify three such metrics pertaining to wireless channel quality, AP capacity in the presence of interference, and client contention. We modify the low level software functionality (firmware and microcode) of a commercial wireless adaptor to measure the necessary quantities. We then test, in a real testbed, the ability of each metric to capture end user throughput through a range of diverse network conditions. Our experimental results indicate that user affiliation decisions should be based on metrics that do not only reflect physical layer performance, or network occupancy, but also concretely capture MAC layer behavior. Based on the acquired insight, we propose a new metric that is shown to be highly accurate across all tested network scenarios.

Despite their widespread deployment, many aspects of wireless network performance are poorly understood, and there is great room from improvement in wireless network reliability and performance. A key obstacle to understanding and improving wireless networks has been the lack of a realistic yet flexible experimental methodology. Physical layer wireless network emulation promises to achieve much of the flexibility of wireless simulators while maintaining much of the realism of real wireless networks. We have developed a software architecture that tames the complexity of physical layer wireless network emulation, and presents users with a powerful yet ease-to-use interface. We present several case studies showing how this software architecture allows complex wireless experiments to be conducted in an efficient manner while still enabling novice users to quickly run simple experiments.

The problem of service delivery over heterogeneous wireless access networks is quite complex and is a topic of ongoing research. Although a unifying aspect of current packet based wireless access technologies is that all of them support IP transport, a common architecture that would allow a mix of autonomous heterogeneous wireless networks to coexist and inter work to provide ubiquitous service using the best network for service delivery at any location does not currently exist. Such a common architecture is essential to enable interoperability across autonomous wireless systems. This paper provides components of a common architectural solution that enables automatic network selection at user terminals with network assistance. It defines new network layer nodes along with new functionality for some of the existing nodes in current systems. A concept of directory assistance type of functionality is introduced where the network could inform the user terminal about the best suited network for the requested service. The proposed architecture allows the user terminal to intelligently and automatically select the network, based on several parameters including service to be used, network QoS capabilities and current network conditions. The proposed architecture is flexible and would enable a variety of business models through different deployment scenarios.

A promising new class of wireless networks has recently emerged, the so-called Wireless Mesh Networks (WMNs). WMNs inherit many advantages from both wired infrastructure and also ad-hoc networks. However, in spite of their distinct characteristics, they also face many technical problems that were present in older classes of wireless networks, such as wireless LANs or pure ad-hoc networks. The much discussed hidden terminal problem is one of them. We argue that an accurate analysis of the effect of hidden nodes in the performance of a random access protocol is still an open issue. In this paper we show the problems and the limitations stemming from common assumptions used in the literature and propose a novel method of modeling time that uses a fixed size channel slot as the unit of time in order to take into account the desynchronisation of nodes. Finally we apply our general method to the classic hidden terminal problem incorporating an iterative step. The proposed analytical model is shown to have a very good match to simulation results for an IEEE 802.11 MAC protocol.

Recently, wireless LAN is achieving remarkable growth, and maturity. On the other hand, by the advance of the Internet, the demand for the multimedia communication services which include video and voice will be expected to grow. Therefore, in the future, the mechanism of QoS guarantee must be realized even in wireless LAN environment. So far, IEEE 802.11e EDCF has been proposed, which is a contention based channel access method to achieve the QoS guarantee in wireless LAN. However, this cannot realize the desired throughput ratio or deterministic target throughput in principle. In this paper, we expand the EDCF to solve such QoS issues and enable more flexible QoS control. Moreover, we show the effectiveness of our proposal by computer simulation.

The advances in the wireless technology, represented by the improved computational capabilities of third generation (3G) and fourth generation (4G) wireless devices and the wider bandwidth wireless networks, make it possible to support a variety of security-sensitive applications such as m-banking and m-commerce. This, however, requires increasingly robust End-to-End security solutions.The contribution of this paper is twofold. First, it presents a design and an implementation of a light weight application-level security solution for handheld devices in wireless LAN. Second, it analyzes the impact of the processing power, time, and memory on the performance of two of the widely known encryption algorithms—RC4 and AES—used by the lightweight handheld devices in the wireless network environment.The work in this paper uses pure Java components to provide end-to-end client authentication and data confidentiality and integrity between wireless J2ME-based clients and J2ME-based servers.

Deployments of wireless LANs consisting of hundreds of 802.11 access points with a large number of users have been reported in enterprises as well as college campuses. However, due to the unreliable nature of wireless links, users frequently encounter degraded performance and lack of coverage. This problem is even worse in unplanned networks, such as the numerous access points deployed by homeowners. Existing approaches that aim to diagnose these problems are inefficient because they troubleshoot at too high a level, and are unable to distinguish among the root causes of degradation. This paper designs, implements, and tests fine-grained detection algorithms that are capable of distinguishing between root causes of wireless anomalies at the depth of the physical layer. An important property that emerges from our system is that diagnostic observations are combined from multiple sources over multiple time instances for improved accuracy and efficiency.

Wireless networks are becoming increasingly popular in professional environments as well as in the home. The success of IEEE 802.11 has cut down equipment costs and people are now building their own residential wireless networks, connecting PCs, MP3 players, broadband gateways and Hi-Fi systems.However, such dramatic growth is creating problems in crowded areas, as the Wi-Fi bandwidth is limited and interference effects start to limit the technology usability.This paper describes a management system for handling the quality of the overall home wireless network, so that interference or bulk noise effects can be alleviated allowing users to enjoy digital content with the reliability they expect. By means of Universal Plug 'n Play, events that may deteriorate the quality of existing services can be propagated to all interested devices so that a smart allocation of network resources can be applied. A simple Admission Control scheme is also used to regulate the admission of real-time streams. Copyright 2006 ACM.

We develop an analytical model of rate adaptive Wireless LAN and downlink traffic flows to randomly located users in the range of an access point. We first calculate the service time distribution of packets being served by the access point. Then, we show that the location of each user determines the throughput that all other users may achieve. Finally we verify our findings with simulations.

State Based Key Hop (SBKH) protocol provides a strong, lightweight encryption scheme for battery operated devices, such as the sensors in a wireless sensor network, as well as small office home office (SOHO) users. Although SBKH can be applied to many underlying protocols, in this paper, we focus on integrating SBKH with 802.11. Hence we compare SBKH with other 802.11 security protocols and show that SBKH eliminates all the issues with wired equivalent privacy (WEP) protocol, using the existing hardware and software as much as possible at a power and processing cost that is much lower than WiFi Protected Access (WPA) 1.0 or 2.0, and is cheaper than WE.

Development in Wireless LAN and Cellular technologies has motivated recent efforts to integrate the two. This creates new application scenarios that were not possible before. Vehicles with Wireless LAN radios can use other vehicles with both Wireless LAN and Cellular radios as mobile gateways and connect to the outside world. We aim to study the feasibility of such global connectivity from the road through simulation of the underlying connectivity characteristics for varying traffic and gateway densities. The connectivity results suggest that each vehicle should be able to connect to at least one gateway for a majority of time. The average path lifetimes are found to be good enough many traditional Internet applications like FTP and HTTP. The effectiveness of the AODV wireless ad-hoc routing protocol over this scenario is evaluated and shown to perform well for the densities considered. However, the routes created by AODV can break very frequently due to the dynamic nature of mobility involved. We introduce a couple of prediction based routing protocols to minimize these route breakages and thus improve performance. These protocols take advantage of some deterministic characteristics of the mobility model to better predict route breakages and take preemptive action.

This paper considers the problem of using wireless LAN location-sensing for security applications. Recently, Bayesian methods have been successfully used to determine location from wireless LAN signals, but such methods have the drawback that a model must first be built from training data. The introduction of model error can drastically reduce the robustness of the location estimates and such errors can be actively induced by malicious users intent on hiding their location. This paper provides a technique for increasing robustness in the face of model error and experimentally validates this technique by testing against unmodeled hardware, modulation of power levels, and the placement of devices outside the trained workspace. Our results have interesting ramifications for location privacy in wireless networks.

Wireless LANs (WLAN), using the IEEE 802.11b standard, have been shown to be inherently insecure. Given the widespread use of this type of WLAN for public and corporate access, it is important to have an "idiot proof" method for securing WLAN from hacking, sniffing, and unauthorized access.In this paper, we present a simple solution using IPSEC that provides an inexpensive, easy to implement, wireless gateway, and an access point that is secure. The client configuration involves no additional software, and the simple steps needed to configure a client are provided using a captive portal. Thus, the gateway is designed to minimize the intrusion to the end user, will only be slightly different from using a standard wireless network, and will require no additional software or hardware.

Understanding usage patterns in wireless local-area networks (WLANs) is critical for those who develop, deploy, and manage WLAN technology, as well as those who develop systems and application software for wireless networks. This paper presents results from the largest and most comprehensive trace of network activity in a large, production wireless LAN. For eleven weeks we traced the activity of nearly two thousand users drawn from a general campus population, using a campus-wide network of 476 access points spread over 161 buildings at Dartmouth College. Our study expands on those done by Tang and Baker, with a significantly larger and broader population.We found that residential traffic dominated all other traffic, particularly in residences populated by newer students; students are increasingly choosing a wireless laptop as their primary computer. Although web protocols were the single largest component of traffic volume, network backup and file sharing contributed an unexpectedly large amount to the traffic. Although there was some roaming within a network session, we were surprised by the number of situations in which cards roamed excessively, unable to settle on one access point. Cross-subnet roams were an especial problem, because they broke IP connections, indicating the need for solutions that avoid or accommodate such roams.

The growing popularity of IEEE 802.11 has made wireless LAN a potential candidate technology for providing high speed wireless access services. Also, by supporting Mobile IP, wireless LAN can meet demands for expanded wireless access coverage while maintaining continuous connectivity from one wireless LAN to another. In the Mobile IP procedure, mobile node movement can be detected from advertisements of foreign agents that differ from the previously received advertisement and the new "care-of" address is registered with the home agent. However, user packets are not forwarded to the new foreign agent until registration is completed and this interruption may degrade the quality of service especially in real-time applications such as audio and video or may lower the TCP throughput due to retransmission timeout. To tackle these issues, we propose a new low latency handoff method, where access points used in a wireless LAN environment and a dedicated MAC bridge are jointly used to alleviate packet loss without altering the Mobile IP specifications. In this paper, we present the design architecture of the proposed method and evaluate its performance in an actual network environment to verify the effectiveness of our approach.

Fairness is an important issue when accessing a shared wireless channel. With fair scheduling, it is possible to allocate bandwidth in proportion to weightsof the packet flows sharing the channel. This paper presents a fully distributed algorithm for fair scheduling in a wireless LAN. The algorithm can be implemented without using a centralized coordinator to arbitrate medium access. The proposed protocol is derived from the Distributed Coordination Function in the IEEE 802.11 standard. Simulation results show that the proposed algorithm is able to schedule transmission such that the bandwidth allocated to different flows is proportional to their weights. An attractive feature of the proposed approach is that it can be implemented with simple modifications to the IEEE 802.11 standard.