In Vehicular Ad-hoc Networks (VANETs), fast and reliable dissemination of safety messages is a key step toward improving the overall road safety. In a highly dynamic VANET environment, safety message dissemination in a multi-hop manner is a challenging and complex problem that has gained significant attention recently. Many protocols and schemes have been proposed to efficiently share safety messages among vehicles. However, most existing techniques do not perform well under real-world traffic conditions, or perform adequately only under very limited scenarios and traffic conditions. This research proposes a highly efficient and reliable multi-hop broadcasting protocol, Intelligent Forwarding Protocol (IFP), that exploits handshake-less communication, ACK Decoupling, and an efficient collision resolution mechanism. In this research, IFP has been extensively studied and evaluated to establish its robustness and superiority over existing schemes. A key contribution of this paper is to present an in-depth analysis and optimization of IFP using theoretical modeling, thorough simulations, and extensive real-world experimentation. With IFP, the message propagation delay is significantly reduced and packet delivery ratio is drastically improved.

Online advertising is one of the primary funding sources for various of content, services, and applications on both web and mobile platforms. Mobile in-app advertising reuses many existing web technologies under the same ad-serving model (i.e., users - publishers - ad networks - advertisers). Nevertheless, mobile in-app advertising is different from the traditional web advertising in many aspects. For example, malicious app developers can generate fraudulent ad clicks in an automated fashion, but malicious web publishers have to launch click fraud with bots. In spite of using the same underlying web infrastructure, advertising threats behave differently on the two platforms.

In this work the Doppler effect is exploited for identifying a collision between two vehicles under Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) conditions. A measurement campaign at 5.9GHz is conducted to observe the Doppler effect for Vehicle-to-Vehicle (V2V) networks. In our previous work, we developed a collision avoidance estimator based on tracking the LOS Doppler shift in the Doppler domain. We now report real-world captures of the Doppler phenomenon in terrestrial V2V networks during a collision and present a method for collision identification by tracking the NLOS Doppler spread in the channel. The classification method by Cepstral coefficients is shown to be reliable in NLOS and LOS conditions, allowing for 360-degree coverage of the vehicle using a single omni-antenna. Through machine learning, classification of collision feature observations is accurate with an accuracy of nearly 100% and reliable with a misclassification rate less than 1%.

This work presents a novel method we call: Frequency Injection Interfacing (FII), for OFDM communication systems. With FII, an external system or observer can communicate to an OFDM receiver through a frequency encoder that injects additional frequency content into the received signal. Specifically, the null subcarriers at the edges of the OFDM waveform are turned on or off to represent a binary code word which references a lookup table. OFDM transmitters do not broadcast wireless energy in the OFDM sidebands in order to comply with regulatory policies. To avoid violating transmission laws, FII uses a direct connection between the frequency encoder and OFDM receiver. Because FII can deliver a unique code word per packet in real time, FII could potentially allow new applications and optimizations for OFDM systems, without requiring a separate application program interface. The FII method is validated through experimentation using software defined radios, a GNU Radio IEEE 802.11 receiver, and a COTS vehicle-to-vehicle radio. A packet reception rate above 95% proves FII operates transparently within existing OFDM architectures, furthermore the non-optimized implementation of FII presented in this work reveals that FII could reliably deliver up to 2047 code words with 67% success and zero false alarms.

The IEEE 1609.4 standard allows a single radio device to utilize multiple channels by alternating control channel (CCH) and service channel (SCH). During the SCH interval, the RTS/CTS/data/ACK handshake can be triggered to transmit large size of data without the hidden node problem. However, it can cause the exposed node problem that hinders concurrent transmissions, which is fatal in highly dynamic VANETs. Even though judicious SCH selection in a multi-channel environment can mitigate the exposed node problem, IEEE 1609.4 does not specify how to select a SCH, which can cause the randomly selected SCHs to be biased. Conforming to the current standards, we therefore propose a novel scheme that enables the exposed vehicles to avoid selecting the same SCH by piggybacking a candidate SCH selection within the optional field of the basic safety message. Through extensive simulations, it is verified that the average throughput can be improved by up to 26%.

For human-driven as well as autonomous vehicles, one of the key requirements is continuous awareness of the surroundings to detect any potential threats (vehicles, pedestrians, wild-life etc.). This requires continuous cooperation between the vehicles by efficiently sharing safety information in a timely manner. However, this is a multi-dimensional and challenging problem due to the complex nature of the vehicular environment. To solve this problem, this paper proposes an elegant solution to efficiently share the safety information among vehicles by using only Basic Safety Messages (BSM), which are part of the existing V2V standards. Through this research, the vehicles are able to quickly and preemptively identify potential threats, not only in their close proximity, but also those which are further along the roadway by intelligently exchanging safety information between neighboring vehicles. Additionally, for the first time, the proposed architecture presents a practical approach of incorporating the onboard sensor data with the V2V communications. This leads to vehicles having improved visibility and situational awareness further outside of their one-hop coverage. Simulation results show that improved visibility of vehicles up to 2.6 km can be achieved while placing minimum overhead and complexity on the network.

The Doppler effect is typically an impairment for wireless communications in mobile-to-mobile environments. Multipath effects leading to delay dispersion at the receiver can create a challenging doubly selective time-frequency channel response. In Vehicle-to-Vehicle (V2V) communications, small-scale effects of the V2V channel over short durations are well understood. However, observing the Doppler response over longer durations can provide observations directly related to the vehicle dynamics. Understanding the channel contributions of the Doppler response in the macro could enable context aware Doppler sensing leading to enhanced collision avoidance or location based services. To model the large-scale Doppler channel response, geometry-based stochastic channel models (GSCM) provide the best representation of how the Doppler profile is changing with the vehicle motion (or lack of). In this novel work, we build upon an existing GSCM by including the double-bounced scattering off the participating vehicles themselves and validating these contributions through real-world experimentation. The model enables the study of a potentially new "sensor" in connected vehicle networks: the large-scale Doppler response, in which mobile scatters are observable and the V2V radio can be aware of the surrounding communication environment.

The current IEEE 1609.4 standard defines multi-channel operations to alternate control and service channel intervals during a period of 100ms. However, there is no mention of service channel selection for a service provider, which allows hidden service providers to select the same service channel. This limitation can cause the hidden terminal problem during the service channel intervals, leading to significant performance deterioration. Without modifying the existing standards, our proposed scheme enables hidden service providers to avoid selecting the same service channel by delivering their candidate service channel number in the optional field of the basic safety message (BSM). Through extensive simulations, it is verified that the packet reception ratio can be improved by up to 23% in typical broadcast scenarios.

To date, app developers are allowed to monetize their apps in two services: in-app advertising and in-app billing. Of these two, in-app billing is not prevalently used by users, whereas in-app advertising is considered an important funding source for developers. However, this service incurs a number of criticisms: (1) users must passively receive all mobile ads while using apps, (2) users get nothing from viewing or clicking ads, (3) ad networks transfer user private information to remote servers in an unencrypted format without user consent, and (4) negative impressions brought from irrelevant ads may harm the advertised brands. To overcome these problems, we propose In-App AdPay, a framework that combines the advantages of "in-app advertising" and "in-app billing" together so that ad networks can overtly ask users' permissions in order to serve more tailored ads, but in return, advertisers will pay targeted users' virtual transactions within the app (e.g., coins in mobile games) via a secure channel. While mobile users can be brought into the monetization loop, it will be technically and legitimately easier for ad networks to study users. We implemented the proof-of-concept framework and conducted a test with 42 volunteers. Based on these studies, we believe that "In-App AdPay" would balance user privacy and user experience without interfering with the existing monetization arrangements. Lastly, we reveal how tracked-by-consent users react in different test scenarios and value the permissions used in ad libraries.

Sharing emergency messages amongst vehicles on the road can greatly reduce traffic accidents. In Vehicular Ad Hoc Networks (VANETs) to share these emergency messages, fast and reliable message dissemination is the key objective in a highly dynamic VANET environment. This research proposes a novel broadcasting protocol to achieve these goals by introducing handshake-less broadcasting, ACK Decoupling and efficient collision resolution mechanism. A key contribution of this paper is to analyze and optimize the broadcasting algorithm using thorough mathematical modeling with extensive simulations. With the suggested optimization process, the message propagation delay can be significantly reduced.

Vehicle-to-Vehicle (V2V) communication is expected to make a global impact on improving driver safety by alerting motorists of potential collisions, but the full safety benefit can only be realized if every vehicle is equipped with a transceiver. Motivated to provide collision avoidance for drivers of vehicles only equipped with a V2V transceiver, we develop a framework for using the V2V communication signal simultaneously as a radar without suggesting any changes to the existing V2V standards or spectrum. The theoretical system treats the IEEE 802.11p waveform as a Multi-Frequency Continuous Wave signal to estimate the velocity and range of a vehicular threat not equipped with a V2V transceiver. While spectrum and upper layers of the protocol stack can vary depending on geographic region, the IEEE 802.11p physical layer protocol is adopted globally. Restrictions in waveform design due to IEEE 802.11p standardization are considered and leveraged for enhancing the radar operations. Through a rigorous simulation treatment, the V2V radar system would be capable of detecting a head-on collision with a 35.12% accuracy using only safety message packets. If non-safety packets are included in the detection operation, then up 100% accuracy is achievable.

The periodic broadcast of a safety message (SM) containing vehicle position and motion data is the salient mechanism for providing drivers pre-crash alerts in Vehicle-to-Vehicle (V2V) networks. However, if SMs are compromised or contain erroneous information, drivers may be unaware of impending danger. Even if vehicles were also equipped with active sensors, awareness may not be achievable in severe non-line-of-sight (NLOS) conditions where collision avoidance is needed most. In this work, a novel system for providing collision avoidance using the Received Signal Strength Indication (RSSI) in V2V networks is presented. Experimental observations of RSSI during collision and no-collision outcomes are analyzed to develop the system's prediction methodology, which is then rigorously tested through a simulation environment to assess the detection performance. The proposed system does not use traditional (Received Signal Strength) RSS distance estimation, fingerprinting, or cooperative methods, which depend heavily on a priori knowledge of path loss conditions. Instead, the decentralized system identifies specific trends in RSSI indicative of a collision. In comparison to RSS distance estimation methods, the proposed system is shown to detect over 35% more collisions in a variety of channel conditions, including NLOS.

Modeling large-scale fading effects in Vehicle-to-Vehicle communications (V2V) in the 5.9GHz Dedicated Short Range Communication band has received broad coverage in the literature over the last 15 years. The majority of V2V channel measurement campaigns have focused on describing the expected path loss of the V2V channel through empirical models. The path loss is a channel metric which describes how fast the received signal strength decays with distance. It is well known that the path loss exponent and reference path loss (y-intercept) varies for different environments, but it is not well understood how the channel changes in a given environment relative to lane separation or vehicle orientation. This paper presents an improved path loss model for line-of-sight (LOS) V2V communications at distances less than 100m. The path loss model removes the Gaussian random variable component, typically used to model shadowing in classic power law path loss model, and instead makes the y-intercept and path loss exponent Gaussian random variables. Derived from extensive empirical measurement campaigns in which vehicle orientation, approach direction, and lane separation are considered, the new channel model is compared to experimental data in which the vehicles move at different speeds. The improved path loss model performs a better fit to experimental data than existing path loss models, including two-ray ground reflection, dual-slope piecewise linear, and classic power law.

Vehicular Ad-hoc networks (VANETs) provide a way for a vehicle to deliver various types of information to users or drivers in other vehicles. Distributing a large amount of information such as multimedia messages in a single control channel makes the control channel easily congested. Transmitting multimedia messages through multi-channel to avoid this congestion becomes a feasible solution. However, low-connectivity in a low vehicle density in multi-channel poses unique challenges and can produce connection failure if this issue is not carefully addressed. In this paper, a network coding technique with divide-and-deliver is introduced to solve this unique challenge for delivering multimedia contents through multiple service channels in a low vehicle density. Through the rigorous analytical derivation and extensive simulation, we show the proposed scheme significantly improves reliability with minimum usage of the control channels in a typical VANETs environment.

Vehicular Ad Hoc Networks (VANETs) is an extension of Mobile Ad Hoc Networks (MANETs) to share traffic information and emergency alerts amongst vehicles on the road. To support many applications in VANETs, most studies use GPS to find the furthest node with ACK to ensure successful message reception. However, this ACK procedure can be removed if a channel between the sender and receiver is clear such that the sender can overhear the broadcasted messages from the receiver. If the sender fails, nodes closer to the sender inform the sender of successful rebroadcasting, which serves as an ACK to the sender. This process will either entirely remove costly ACKing processes or at least decouple the messages propagation from ACKing to the sender, which will significantly improve the speed of message propagation. In this paper, we use Signal-to-Noise Ratio (SNR) with ACK decoupling to ensure fast message propagation with reliable message recovery. Detailed simulation results show that the proposed SNR based approach with ACK decoupling outperforms the Smart Broadcast (SB) by 200% in average throughput and per hop delay, while ensuring the reliable dissemination of emergency messages in typical VANETs environments.

Cryptographically-Curated File System (CCFS) proposed in this work supports the adoption of Information-Centric Networking. CCFS utilizes content names that span trust boundaries, verify integrity, tolerate disruption, authenticate content, and provide non-repudiation. Irrespective of the ability to reach an authoritative host, CCFS provides secure access by binding a chain of trust into the content name itself. Curators cryptographically bind content to a name, which is a path through a series of objects that map human meaningful names to cryptographically strong content identifiers. CCFS serves as a network layer for storage systems unifying currently disparate storage technologies. The power of CCFS derives from file hashes and public keys used as a name with which to retrieve content and as a method of verifying that content. We present results from our prototype implementation. Our results show that the overhead associated with CCFS is not negligible, but also is not prohibitive.

Providing tools to achieve a high level of safety transportation is the important objective in VANETs research. Hence, most of the works are devoted to developing safety-message dissemination algorithms. However, non-safety applications can also contribute to the network efficiency by exchanging traffic information. To support these applications, VANETs adopt the wireless access in the vehicular environment (WAVE) to guarantee the quality of service (QoS) using four different access categories. However, the WAVE could not provide the QoS to the users due to the collisions caused by the small contention-window size for the top priority traffic when top-priority traffic is dominant. Therefore, this small contention-window size setting for the prioritization induces severe performance degradation. In this paper, the Dynamic Service-Channels Allocation (DSCA) method is proposed to maximize throughput by dynamically assigning different service channels to the users. Theoretical analysis and extensive simulation works suggest that the DSCA improves the average throughput by 22% over the uniform channel allocation method. Moreover, the DSCA can be easily implemented in real devices without any protocol modifications.

As network attacks increase in complexity, network administrators will continue to struggle with analyzing security data immediately and efficiently. To alleviate these challenges, researchers are looking into various visualization techniques (e.g., two-dimensional (2D) and three-dimensional (3D)) to detect, identify, and analyze malicious attacks. This paper discusses the benefits of using a stereoscopic 3D parallel visualization techniques for network scanning, in particular, when addressing occlusion-based visualization attacks intended to confuse network administrators. To our knowledge, no 2D or 3D tool exists that analyzes these attacks. Hence, we propose a novel 3D Parallel coordinate visualization tool for advanced network scans and attacks called P3D. P3D uses flow data, filtering techniques, and state-of-the art 3D technologies to help network administrators detect distributed and coordinated network scans. Compared to other 2D and 3D network security visualization tools, P3D prevents occlusion-based visualization attacks (e.g., Windshield Wiper and Port Source Confusion attacks). We validate our tool with use-cases from emulated distributed scanning attacks. Our evaluation shows P3D allows users to extract new information about scans and minimize information overload by adding an extra dimension and awareness region in the visualization.

A hidden-node problem is one of the major challenges that cause severe performance degradation in wireless ad-hoc networks. Even though RTS/CTS (Request To Send/Clear To Send) exchange can remove the hidden-node problem, the inefficiency of exchanging the RTS/CTS has brought attentions to many researchers. While most of these efforts have been focused on the theoretical analysis, very little efforts were given to the verification of proposed models through real-world experiments. Random-bit error is another important factor that deteriorates the network performance in wireless environments. Through rigorous real-world experiments, this paper demonstrates a feasible methodology to enhance network throughput in the existence of hidden nodes by using optimal fragments. Our previous analytical model that incorporates the impact by random-bit error and hidden nodes on the throughput is validated under various real-world environments. These experimental results will provide a solid foundation to the research communities in solving the hidden-node problem in noisy MANET environments.

As network attacks increase in complexity, the ability to quickly analyze security data and mitigate the effect of these attacks becomes a difficult problem. To alleviate these challenges, researchers are looking into various two-dimensional (2D) and three-dimensional (3D) visualization tools to detect, identify, and analyze malicious attacks. These visualization tools often require advanced knowledge in networking, visualization, and information security to operate, navigate, and successfully examine malicious attacks. Novice users, deficient in the required advanced knowledge, may find navigation within these visualization tools difficult. Furthermore, expert users may be limited and costly. We discuss the use of a modern recommender system to aid in navigating within a complex 3D visualization for network security applications. We developed a visualization module called NAVSEC, a recommender system prototype for navigating in 3D network security visualization tools. NAVSEC recommends visualizations and interactions to novice users. Given visualization interaction input from a novice user and expert communities, NAVSEC is instrumental in reducing confusion for a novice user while navigating in a 3D visualization. We illustrate NAVSEC with a use-case from an emulated stealthy scanning attack disguised as a file transfer with multiple concurrent connections. We show that using NAVSEC, a novice user's visualization converges towards a visualization used to identify or detect a suspected attack by an expert user. As a result, NAVSEC can successfully guide the novice user in differentiating between complex network attacks and benign legitimate traffic with step-by-step created visualizations and suggested user interactions.

We present the Secure SOurce-BAsed Loose Synchronization (SOBAS) protocol to securely synchronize the events in the network, without the transmission of explicit synchronization control messages. In SOBAS, nodes use their local time values as a one-time dynamic key to encrypt each message. In this way, SOBAS provides an effective dynamic en-route filtering mechanism, where the malicious data is filtered from the network. With SOBAS, we are able to achieve our main goal of synchronizing events at the sink as quickly, as accurately, and as surreptitiously as possible. With loose synchronization, SOBAS reduces the number of control messages needed for a WSN to operate providing the key benefits of reduced energy consumption as well as reducing the opportunity for malicious nodes to eavesdrop, intercept, or be made aware of the presence of the network. Albeit a loose synchronization per se, SOBAS is also able to provide $(7.24 \mu)$s clock precision given today's sensor technology, which is much better than other comparable schemes (schemes that do not employ GPS devices). Also, we show that by recognizing the need for and employing loose time synchronization, necessary synchronization can be provided to the WSN application using half of the energy needed for traditional schemes. Both analytical and simulation results are presented to verify the feasibility of SOBAS as well as the energy consumption of the scheme under normal operation and attack from malicious nodes.

ABSTRACT For wireless mobile multihop relay (MMR) networks, we have chosen orthogonal frequency division multiple access (OFDMA) and time division duplex as a multiple access scheme and a duplex communication technique, respectively. We have also selected nontransparent relay stations (nt‐RSs) as relay nodes to extend the MMR network coverage. Through the nt‐RSs, far‐off subscriber stations (SSs) or hidden SSs can communicate with a base station (BS) that is connected to backhaul networks. In these MMR networks, the way in which a BS and nt‐RSs use OFDMA resources (e.g., OFDMA symbols and subcarriers) and share them might reduce system capacity and network throughput. Therefore, we proposed a new adaptive OFDMA frame structure for both the BS and the nt‐RSs. The proposed scheme is the first approach that incorporates the adaptive technique for wireless MMR networks. Based on the proposed adaptive OFDMA frame structure, an adaptive OFDMA resource allocation for SSs within a BS as well as nt‐RSs was proposed. To derive the maximum OFDMA resource that nt‐RSs can be assigned and to synchronize access zones and relay zones between a superior station and its subordinate nt‐RSs, three properties are introduced: a data relay property, a maximum balance property, and a relay zone limitation property. In addition, we propose max‐min and proportional fairness schemes of the proposed adaptive frame structure. Our numerical analysis and simulations show that the proposed OFDMA allocation scheme performs better than the nonadaptive allocation scheme in terms of network throughput and fairness especially in the asymmetric distribution of subscriber stations between access zones and relay zones in the MMR networks. Copyright © 2011 John Wiley & Sons, Ltd.

Hidden nodes cause unexpected collisions and interferences in mobile ad-hoc networks (MANETs). However, little attention has been given to the behavior of hidden nodes, especially when channels are under random bit errors. Exchanging RTS/CTS can avoid hidden node problems. However, undesirable overheads in every packet cause performance degradation, and this motivates many researchers to design new algorithms with modification of the IEEE 802.11 standard. In this paper, the impact of hidden nodes is thoroughly modeled using Markov chains. This model incorporates critical network parameters (random bit errors, packet lengths, number of users) in noisy MANETs channels. Through rigorous analysis, the study suggests the optimal packet lengths to be used in various channel conditions with the existence of hidden nodes. These optimal fragments effectively reduce the number of retransmissions caused by collisions from hidden nodes and corrupted packets due to random bit errors, which significantly improves throughput in noisy MANETs channels without modification of the standards.

Reliability is a critical concern in disseminating safety messages in vehicular ad-hoc-networks (VANETs). Thus far, redundant broadcast (or next relay broadcast) has been used to ensure reliable transfer of safety messages. However, redundant broadcast fails to meet high-reliability requirement owing to lack of a feedback or acknowledgment (ACK) mechanism. In this work, a power controlled negative-acknowledgment (NACK) mechanism is introduced as a feedback technique to ensure reliable reception of safety messages. Significantly, this work also attempts to cover vehicles present in transmission holes in the broadcast region. Vehicles in the immediate neighborhood detect and recover safety message for a vehicle present in the transmission hole by estimating propagation loss for the vehicle. NACK together with hole detection and recovery mechanism nearly guarantees safety-message delivery in VANETs. Reliability of the proposed technique is formulated mathematically with packet reception ratio (PRR) as the reliability metric. Using theoretical analysis and simulation evaluation in ns-3 we establish that the proposed technique guarantees safety-message reception by mitigating packet loss caused by interference from hidden nodes, and at instances where vehicles are located in the transmission holes.

Network Disaster Recovery research has examined behavior of networks after disasters with an aim to restoring normal conditions. In addition to probable loss of connectivity, a disaster scenario can also lead to security risks. However, network security has been examined extensively under normal conditions, and not under conditions that ensue after disasters. Therefore, security issues should be addressed during the period of chaos after a disaster, but before operating conditions return to normal. Furthermore, security should be assured, while still allowing access to the network to enable public communication in order to assist in disaster relief efforts. In general, the desire to help with public assistance requires opening up access to the network, while security concerns add pressure to close down or limit access to the network. In this study, we show that the objectives of availability and confidentiality, two objectives that have not previously been considered together in disaster scenarios, can be simultaneously achieved. For our study, we evaluated six wireless devices with various network configurations, including a laptop, a Kindle Fire e-reader, an Android tablet, a Google Nexus phone, an IP camera, and an Apple TV, to approximate behaviors of a communication network under a disaster scenario. Actual data leakage was tracked and observed for these devices. To the best of our knowledge this has not previously been examined in a systematic manner for post-disaster scenarios. After illustrating the data leakage of various devices, we analyze the risk associated with the various types of leakage. Moving private traffic to a VPN would free the physical network for use as a public resource.

A network has several attributes which play a role in determining the security of the network and its robustness to external threats. These attributes are related to security through a complex nonlinear function which is generally unknown to the network management personnel. Since the network security is an explicit function of these attributes, the managers do not realize when the value of a certain attribute has become critical to the point of threatening network security. In this paper we take a theoretically rigorous approach to quantifying the effect each of the individual attributes has on the network. By using ideas from probability and decision theory, we can order the significant factors determining network security. This is similar to dimensionality reduction which is commonly employed for model based identification methods. Based on our analysis we can come up with critical coefficients which must be maintained by the administrator if the network is to remain secure to external threats. We show how the mathematical framework leads to the prediction of network's security health, and how real world data can be used to substantiate these claims. Paper concludes by validating our results on a list of compromised machine and determining if our identified metrics played the significant role in the infection.

As the volume of network data continues to increase and networks become more complex, the ability to accurately manage and analyze data quickly becomes a difficult problem. Many network management tools already use two-dimensional (2D) and three-dimensional (3D) visualization techniques to help support decision-making and reasoning of network anomalies and activity. However, a poor user interface combined with the massive amount of data could obfuscate important network details. As a result, administrators may fail to detect and identify malicious network behavior in a timely manner. 3D visualizations address this challenge by introducing monocular and binocular visual cues to portray depth and to increase the perceived viewing area. In this work, we explore these cues for 3D network security applications, with a particular emphasis on binocular disparity or stereoscopic 3D. Currently, no network security tool takes advantage of the enhanced depth perception provided by stereoscopic 3D technologies for vulnerability assessment. Compared to traditional 3D systems, stereoscopic 3D helps improve the perception of depth, which can, in turn reduce the number of errors and increase response times of network administrators. Thus, we introduce a stereoscopic 3D visual Framework for Rendering Enhanced 3D Stereoscopic Visualizations for Network Security (FRE3DS). Our novel framework uses state-of-the art 3D graphics rendering to assist in 3D visualizations for network security applications. Moreover, utilizing our framework, we propose a new 3D Stereoscopic Vulnerability Assessment Tool (3DSVAT). We illustrate the use of 3DSVAT to assist in rapid detection and correlation of attack vulnerabilities in a subset of a modified local area network data set using the enhanced perception of depth in a stereoscopic 3D environment.

Vehicular Ad hoc Networks (VANETs) provide vehicle-to-vehicle and vehicle-to-infrastructure communication using Dedicated Short-Range Communications (DSRC). The core objective of VANETs is to provide safety message communication among vehicles. In dense urban traffic, safety message communication encounters severe packet collisions due to excessive number of nodes contending to access the control channel. In such a complex dense and mobile scenario, an ideal single vehicle per time slot has yet not been achieved. This paper introduces the use of lane level location information to achieve a single vehicle per time slot configuration. The transmission range of a message originator is divided into a grid using distance and lanes as the two variables. Each block within the grid houses a single vehicle at most that is assigned a unique time slot. The contention among nodes for the same time slot is virtually removed. Theory and ns-3 simulation justify the feasibility, and prove that the technique reduces packet collisions by 2%, and improves message dissemination speed by as much as 30% each hop.

Cognitive radio (CR) users are expected to be uncoordinated users that opportunistically seek the spectrum resource from primary users (PUs) in a competitive way. In most existing works, however, CR users are required to share the interference channel information and power strategies to conduct the game with pricing mechanisms that incur the frequent exchange of information. The requirement of significant communication overheads among CR users impedes fully distributed solutions for the deployment of CR networks, which is a challenging problem in the research communities. In this paper, a robust distributed power control algorithm is designed with low implementation complexity for CR networks through reinforcement learning, which does not require the interference channel and power strategy information among CR users (and from CR users to PUs). To the best of our knowledge, this research provides the solution for the first time for the incomplete-information power control game in CR networks. During the repeated game, CR users can control their power strategies by observing the interference from the feedback signals of PUs and transmission rates obtained in the previous step. This procedure allows achieving high spectrum efficiency while conforming to the interference constraint of PUs. This constrained repeated stochastic game with learning automaton is proved to be asymptotically equivalence to the traditional game with complete information. The properties of existence, diagonal concavity and uniqueness for the game are studied. A Bush-Mosteller reinforcement learning procedure is designed for the power control algorithm, and the properties of convergence and learning rate of the algorithm are analyzed. The performance of the learning-based power control algorithm is thoroughly investigated with simulation results, which demonstrates the effectiveness of the proposed algorithm in solving variety of practical CR network problems for real-world applications.

Vehicular Ad-hoc Network(VANET) enables a wireless communication between vehicles to improve driver's safety. For the safety, a message including safety-related information is broadcast between vehicles and forwarded for farther vehicles. VANET poses challenges that broadcast attempts from many vehicles cause collisions between packets and result in packet drops. Many researches have concentrated on removing collisions in those excessive broadcasts. These approaches lead one vehicle to be selected as a rebroadcast vehicle. However, it makes difficult to forward the safety message to all directions at intersections. In this paper, we suggest an efficient way to broadcast a safety message to all directions at an intersection with a short delay and without a collision. Our simulation results show a coverage improvement of as much as 70% and a delay reduction of as much as 100msec.

In the consumer electronics market, the need for error tolerance in wireless systems is increasing especially from I-Q imbalances and non-linearity in RF front-end. In most applications such as encoded image transmission, not all bits are equally important. However, current error tolerance schemes give equal importance to all transmitted bits. In this paper, an OFDM data transfer methodology that has the least impact on image data in the presence of persistent bit errors due to I-Q imbalances and non-linear compression is proposed.

This study provides a general framework for distributed multi-user power control problems in cognitive radio (CR) networks over fading channels. Using a non-cooperative game with coupled constraints in CR and primary channel outages, the fundamental performance traits of power control for multiple CR users are analyzed in the present of multiple primary users (PUs) in fading environments for the first time. While the feasibility of target SINRs are always guaranteed in most studies for no-fading environments, the adopted channel outage model incorporates the probability that the SINR falls below a target threshold due to fast fading or interferences from other CR users. For the tractable analysis of the formulated problem, geometric programming approach is used to transfer it as a convex one. A dual decomposition approach is applied with layered structure for the constrained game, where each subproblem is full of economic interpretation. The properties of Nash Equilibrium (N.E.) for the proposed game are thoroughly investigated. An asynchronous distributed power control algorithm converging to the N.E. is designed, which ensures the robust implementation in fading environments. Finally, the simulation results and analysis are shown to enforce the effectiveness of the proposed algorithms for CR users over fading channels.

Vehicular ad hoc networks (VANETs) rely on multi-hop communication in order to disseminate information to locations beyond the transmission range. In this paper, the use of handshaking mechanism is evaluated against instant transmission for safety message routing in VANETs for the first time. It is argued that due to the small size of VANET safety message (mean payload size of 100 bytes), handshaking may not be advantageous to avoid hidden node problem and may incur overhead delay. The simplified instant broadcast routing without the use of handshake mechanism is recommended. Theoretical analysis of message propagation delay using instant broadcast routing is shown which can be easily extended for any broadcast method. Two prominent handshake based broadcast routing schemes are implemented in ns-3 along with instant broadcast scheme. The simulation results reveal that instant broadcast effectively lowers the message propagation delay by 100% each hop and guarantees reliable dissemination of safety messages to all endangered vehicles on the road.

The growing interest in vehicular ad hoc networks (VANETs) enables decentralized traveler information systems to become more feasible and effective in Intelligent Transportation Systems (ITS). Major challenges in such network environments include varying path characteristics and vulnerable channel quality resulting from dynamic traffic conditions and the design of the road. This paper demonstrates a feasible methodology that can enhance inter-vehicle information dissemination using dynamic optimal fragmentation with rate adaptation algorithm (DORA). DORA achieves maximum goodput in wireless mobile networks by computing a fragmentation threshold and transmitting optimal sized packets with maximum transfer rates. To estimate the SNR in the model, an adaptive on-demand UDP estimator is designed to reduce estimation overhead. Several test-beds were developed to evaluate the performance of DORA in channel estimation accuracy, ad hoc network goodput, and vehicle-to-vehicle network goodput along I-85 in Atlanta, Georgia. The proposed algorithm is an energy-efficient, generic CSMA/CA MAC protocol for wireless mobile computing applications, and enhances system goodput in ad hoc networks and vehicle-to-vehicle networks without modification of the base protocols.

Because of the high cost of construction and maintenance of infrastructure-based networks, researchers have concentrated their efforts on studying wireless mesh/relay networks with lower cost and high scalability. Due to the demand for real-time multimedia communication in heterogeneous networks, IEEE 802.16 multi-hop mesh/relay networks with IEEE 802.11e WLANs for QoS support can be an effective multi-hop network model instead of IEEE 802.11-based mesh networks without any QoS mechanism. In addition, to provide end-to-end QoS support for different QoS mechanisms of IEEE 802.lie, IEEE 802.16, and the Internet protocol, differentiated services architecture can be applied. Therefore, we propose a design of cross-layer DiffServ architecture in wireless multi-hop mesh/relay networks with WLANs for end-to-end QoS support. Simulations of the proposed QoS architecture using OPNET Modeler show an excellent end-to-end QoS guarantee in the multi-hop mesh/relay networks.

Given that transmission cost is significant in a Wireless Sensor Network (WSN), sending explicit keying control messages significantly increases the amount of energy consumed by each sensing device. Thus, in this paper, we address the issue of security for WSNs from a completely novel perspective. We present a technique to secure the network, without the transmission of explicit keying messages needed to avoid stale keys. Our protocol, the TIme-Based DynamiC Keying and En-Route Filtering (TICK) protocol for WSNs secures events as they occur. As opposed to current chatty schemes that incur regular keying message overhead, nodes use their local time values as a one-time dynamic key to encrypt each message. Further, this mechanism prevents malicious nodes from injecting false packets into the network. TICK is as a worst case twice more energy efficient than existing related work. Both an analytical framework and simulation results are presented to verify the feasibility of TICK as well as the energy consumption of the scheme under normal operation and attack from malicious nodes.

This paper studies the repeated power control game in cognitive radio (CR) networks through reinforcement learning without channel and power strategy information exchange among CR users. Unlike traditional game-theoretical approaches on CR power control, this research solves the incomplete information power control problems for selfish and autonomous CR users for the first time. Each CR user in the problem only knows its own channel and power strategy while the information of primary users (PUs) and other different types of CR users are unknown. The formulated power control problem is a constrained repeated stochastic game with learning automaton. The objective of this repeated game is to maximize the average utility of each CR user under the interference power constraints of PUs. At each time step, the CR user only knows its own utility and the interference functions after the play but no further information. This power control game is proved to be asymptotically equivalent to the traditional game theory approaches. The properties of existence, diagonal concavity and uniqueness for this game are illustrated in detail. A Bush-Mosteller reinforcement learning procedure is designed for the power control algorithm. Finally, the learning based power control algorithm is implemented, and the simulation results with detailed analysis are shown to enforce the effectiveness of the proposed algorithms.

Cognitive radio ad hoc networks (CRAHNs) solve the problem of spectrum utilization when the licensed or primary user (PU) activity changes over time. This affects not only the spectrum availability, but also the network topology, making the analysis of scaling laws very challenging. Currently, the effect of PU activity on the network scaling laws has not been theoretically analyzed, to the best of our knowledge. In this paper, throughput capacity and delay scaling laws are introduced for CRAHNs by capturing the impact of PU activity in dense, and sparse PU deployment conditions. In the former case, it is observed that the scalability for the CRAHN is very low, with the capacity strongly related to the 'off' transmission times of the PU. Moreover, this is possible only under specific conditions of buffering, and queuing assumptions for the CRAHN. In the second case with sparse PUs, both the average throughput capacity and network delay of CRAHN are significantly improved. Interestingly, in both cases, the distribution of the PU locations does not impact the scalability in CRAHNs.

Understanding and analyzing the past and current behavior of the Internet will be instrumental in building tomorrow's more efficient and scalable networks (e.g., the future Internet). In this paper, we study the impact of Autonomous Systems (ASs) paths' end-to-end latency. Unfortunately, due to the diverse set of non-disclosed routing policies among ASs, packets belonging to a certain end-to- end connection may traverse different ASs, causing fluctuating AS paths. Fluctuation of AS paths has been studied in the literature directly from the core of the network. In this paper, we take a different approach to the analysis of the fluctuation, solely from the edge of the network. Specifically, from the end user's perspective, some AS paths may be optimal (or better) and some sub-optimal. Furthermore, there is not a unique definition for sub- optimality as it may be reflected with various measures (e.g., latency) depending on the application requirements and expectations. In this paper we analyze fluctuating AS path lengths (ASPLs) and investigate their impact on the end-to-end latency over the Internet at a greater scale than previous studies. This study was conducted using Scriptroute to probe various PlanetLab nodes. Our results show that all of the source nodes experienced some AS path differences and the ASPL values that the sources use greatly vary. At worst, some nodes experienced different paths over 70% of the time during our measurements. We observed that the largest difference in ASPLs on a particular connection was as high as 6 with an average of 2.5. Moreover, we present real cases where ASPL and latency values are related, inversely related, and not related at all. Finally, we provide a simple definition for suboptimality and analyze the collected data against this definition. We show that overall 82% of the fluctuating paths and 9% of all the traces between source-destination pairs faced sub-optimal AS paths.

In this paper, we propose a mutual authentication and key agreement scheme for V2I communications. Our scheme improves security and privacy protection compared with the existing protocols. We consider common driver's tendency to design a more efficient scheme. The results of the security and performance analysis show that our scheme is suitable for practical use in terms of security, privacy, and performance.

Designing cost-efficient, secure network protocols for Wireless Sensor Networks (WSNs) is a challenging problem because sensors are resource-limited wireless devices. Since the communication cost is the most dominant factor in a sensor's energy consumption, we introduce an energy-efficient Virtual Energy-Based Encryption and Keying (VEBEK) scheme for WSNs that significantly reduces the number of transmissions needed for rekeying to avoid stale keys. In addition to the goal of saving energy, minimal transmission is imperative for some military applications of WSNs where an adversary could be monitoring the wireless spectrum. VEBEK is a secure communication framework where sensed data is encoded using a scheme based on a permutation code generated via the RC4 encryption mechanism. The key to the RC4 encryption mechanism dynamically changes as a function of the residual virtual energy of the sensor. Thus, a one-time dynamic key is employed for one packet only and different keys are used for the successive packets of the stream. The intermediate nodes along the path to the sink are able to verify the authenticity and integrity of the incoming packets using a predicted value of the key generated by the sender's virtual energy, thus requiring no need for specific rekeying messages. VEBEK is able to efficiently detect and filter false data injected into the network by malicious outsiders. The VEBEK framework consists of two operational modes (VEBEK-I and VEBEK-II), each of which is optimal for different scenarios. In VEBEK-I, each node monitors its one-hop neighbors where VEBEK-II statistically monitors downstream nodes. We have evaluated VEBEK's feasibility and performance analytically and through simulations. Our results show that VEBEK, without incurring transmission overhead (increasing packet size or sending control messages for rekeying), is able to eliminate malicious data from the network in an energy-efficient manner. We also show that our framework performs better than other comparable schemes in the literature with an overall 60-100 percent improvement in energy savings without the assumption of a reliable medium access control layer.

Various vehicular communication technologies have been proposed to provide reliable and seamless wireless communications. Short-range vehicular communications can be established using IEEE 802.11p, and the range of these protocols can be extended using mobile multi-hop ad hoc networks. To provide consistent quality of service (QoS) with maximum achievable transmission rate, many algorithms assume that the signal to noise ratio (SNR) of the receiver is known, or can be obtained by modifying protocols. In this paper, we present an efficient on-demand adaptive channel estimation technique. Using simple UDP messages without changing protocols, the estimator predicts the SNR with minimum signaling overheads. Extensive experiments in vehicular environments along the I-85 highway and residential areas in Atlanta, Georgia reinforce that the proposed algorithm is efficient and reliable channel estimation technique for next generation wireless mobile networks.

we apply the concept of the common spectrum coordination channel (CSCC) etiquette protocol to form a spectrum sharing protocol among access points in 802.11 networks. It efficiently allocates operating frequencies among access points. As a result, it reduces interference from wireless devices using the 802.11 MAC/PHY protocol. This is motivated by the lack of intelligent spectrum sharing among Wi-Fi access points. We show that the CSCC protocol is not suitable for point to multipoint (PMP) networks. Through simulation, our proposed spectrum sharing protocol improves throughput and reduces media access delay in Wi-Fi networks.

Due to the high cost of construction and maintenance of infrastructure, engineers and researchers have focused their investigations on wireless mesh/relay networks with lower cost and high scalability. For current wireless mesh/relay networks, the end-to-end QoS guarantee is an important functionality because the demand for real-time multimedia communications has recently been increasing. Therefore, We propose an adaptive end-to-end delay assurance algorithm with the differentiated services architecture of hybrid mesh/relay networks with IEEE 802.16 and IEEE 802.11e to support a QoS guarantee for the mesh/relay networks. By simulating the mesh/relay networks using OPNET Modeler and analyzing the traffic of applications with different QoS requirements, we show that the proposed algorithm with the differentiated services architecture provides excellent end-to-end QoS support.

WiMAX with wired infrastructure has been popularly deployed. However, due to the high cost of the construction and the maintenance of the infrastructure, researchers have focused their investigations on IEEE 802.16 wireless multi-hop networks with low cost and high scalability. With IEEE802.11e WLANs, which provide user-level QoS support for WLANs, the multi-hop networks of IEEE 802.16 using DiffServ can provide an excellent network architecture for QoS support. In the multi-hop networks, polling services for the bandwidth request and grant play an important role for a QoS guarantee for IEEE 802.11e clients. Thus, we propose an adaptive polling algorithm with differentiation strategy for unicast and multicast polling services in IEEE 802.16 multi-hop networks with IEEE 802.11e WLANs using DiffServ to provide a QoS guarantee. By simulating the polling algorithm and the DiffServ network architecture using the OPNET Modeler and analyzing bandwidth utilization and the number of clients with rejected bandwidth requests, we show that the novel polling algorithm provides excellent QoS support.

To support the quality of service in wireless multimedia communications, wireless systems should work well in typical wireless environments characterized by the path loss of the signals, multipath fading, interference to adjacent channels, and random errors. A variety of researches in the application-layer have been proposed to adapt the video encoder to the link quality by compressing the data with different rates. However, these approaches introduce additional overhead and are inefficient when the round-trip delays are long. This paper proposes an algorithm to prevent packet losses and skipped frames by using optimal fragmentation technique with rate adaptation. Using an adaptive SNR estimator, the sender estimates the SNR of the receiver, and shapes arbitrary sized packets into optimal length packets with rate adaptation. Through rigorous analysis and extensive experiments with an implemented test-bed, we show that the algorithm significantly enhances the visual quality of real-time multimedia streaming in noisy ad hoc networks. The experimental results reinforce the fact that the algorithm is a realistic approach that can be deployed without modifying existing standards.

Abstract Worldwide interoperability for microwave access (WiMAX), designed by the IEEE 802.16 standards group, is one of the most promising broadband wireless technologies with respect to delivering high‐speed connectivity in the last mile. A mesh network configuration was added for improved coverage and throughput. We describe security concerns for WiMAX mesh mode such as malicious sponsor nodes and privacy. We also seek to reduce the processing load as a result of the use of link encryption. We introduce two different types of attacks as a result of different types of malicious sponsor nodes. The first type of attack occurs when the malicious sponsor node has not actually joined the current mesh network but solicits new nodes to join the mesh network through it. The second type of attack occurs when the malicious node is a member of the mesh network and selectively drops data from its child nodes. To prevent the first attack, we propose a new security protocol that adds to the standard control messages a pair of secret authorization keys (AK). To handle the second attack, we propose a reputation‐based scheme that is specific to WiMAX mesh networks. We conduct a numerical analysis and simulations to highlight the strengths of the proposed schemes. The proposed reputation‐based scheme uses the MSH‐NCFG control message that is used in the WiMAX standard to send reputation information about nodes in the mesh network. Nodes that are joining the mesh network receive and process MSH‐NCFG messages and decide which sponsor node through which to join the network. We conduct a numerical analysis to determine the amount of time for reputation information to propagate through the mesh network, thus allowing joining nodes to avoid malicious sponsor nodes. The simulation results show that the proposed scheme can reduce the overall data drop rate in WiMAX mesh networks in the presence of the aforementioned attacks from malicious sponsor nodes. Copyright © 2009 John Wiley & Sons, Ltd.

Packet based wireless networks have provided high data rates, and the desire for ubiquitous wireless computing is growing rapidly. To accommodate these demands, wireless systems should work well in typical wireless environments. The most widely deployed WLAN technology, IEEE 802.11, uses the unlicensed ISM band, which is vulnerable to noise generated by electronic devices. This paper proposes a way to enhance system goodput in CSMA/CA MAC protocols using fragmentation. Our analytical model considers the number of contending stations, packet collisions, packet error probabilities, and fragmentation overheads. With extensive experiments in WLAN and ad hoc networks, we show the optimization improves the goodput approximately 18% in a typical WLAN and 48% in ad hoc networks. The proposed approach can be implemented to any CSMA/CA MAC protocol without modifying the standard.

We propose a routing overlay system, MobCast, for simple and efficient routing to mobile hosts. Mobcast nodes advertise the same address space at each proxy location, and each mobile host is assigned a "universal" IP address from this address space, so packets sent to a mobile host's universal IP address automatically go to the nearest proxy on the overlay. The overlay then delivers the packets to the mobile host. Our architecture enables seamless mobility for both micro and macro mobility. While our initial design is not as mature as Mobile IP, it shows great promise to solve the traditional problems of ingress routing, firewalls, NATs, and rapid mobility with much lower complexity. We present our design as a scalable and deployable alternative to mobile IP. In this paper, we focus on describing the MobCast system architecture. We form our arguments for scalability, handoff-speed, and simplicity, and give our initial results for scalability. We postpone a detailed discussion of MobCast's security model for future work.

IEEE 802.11 wireless networks are plagued with problems of unauthorized access. Left undetected, unauthorized access is the precursor to additional mischief. Current approaches to detecting intruders are invasive or can be evaded by stealthy attackers. We propose the use of spectral analysis to identify a type of wireless network interface card. This mechanism can be applied to support the detection of unauthorized systems that use wireless network interface cards that are different from that of a legitimate system. The approach is passive and works in the presence of encrypted traffic.

We developed a tool to help network administrators deal with the large amount of alarms generated from network security appliances. It efficiently uses screen space representing a high number of IP addresses along with time sequence so that general alarm activity for a network can be visualized along with details, if desired. The tool was useful but encountered problems when there was a significant increase in the amount of alarms. The issues that resulted are addressed in this paper along with methods to ease them.

Current tools for forensic analysis require many hours to understand novel attacks, causing reports to be terse and untimely. We apply visual filtering and tagging of flows in a novel way to address the current limitations of post-attack analysis, reporting, and sharing. We discuss the benefits of visual filtering and tagging of network flows and introduce FlowTag as our prototype tool for Honeynet researchers. We argue that online collaborative analysis benefits security researchers by organizing attacks, collaborating on analysis, forming attack databases for trend analysis, and in promoting new security research areas. Lastly, we show three attacks on the Georgia Tech Honeynet and describe the analysis process using FlowTag.

Use of private addresses in a mobile node's home network brings a challenge to mobile IP because a private address cannot uniquely identify the mobile node in the public network. Here we present an approach that a mobile node whose private home network is isolated from the public network by a realm specific IP (RSIP) gateway can communicate with a correspondent node when the mobile node visits the public network. Our solution neither uses any private addresses in the public network nor brings any additional security issues. In this paper, our methods are explained, and detailed procedures as well as packet formats are illustrated

The superior reconfigurability of software defined radio mobile devices has made it the most promising technology on the wireless network and in the communication industry. Despite several advantages, there is still a lot to discuss regarding security. One of the more dangerous threats in SDR wireless communication is cloning. Besides illegal billing, cloned units increase the competition of shared resources, the network congestion and degrade network services. In this paper, an anti-cloning framework for software defined radio mobile devices is proposed. In the framework, the SDR mobile device together with the wireless operator is responsible for detecting if it has been cloned or not. Another key point is that the framework is independent of the wireless communication technology, working well for different cellular technologies and the Internet. New pieces of hardware and new protocols are specified to avoid network services being used by cloned units. Proofs that analyze correctness of the protocols and the framework are also presented.

The massive amount of alarm data generated from intrusion detection systems is cumbersome for network system administrators to analyze. Often, important details are overlooked and it is difficult to get an overall picture of what is occurring in the network by manually traversing textual alarm logs. We have designed a novel visualization to address this problem by showing alarm activity within a network. Alarm data is presented in an overview where system administrators can get a general sense of network activity and easily detect anomalies. They then have the option of zooming and drilling down for details. The information is presented with local network IP (Internet Protocol) addresses plotted over multiple yaxes to represent the location of alarms. Time on the x-axis is used to show the pattern of the alarms and variations in color encode the severity and amount of alarms. Based on our system administrator requirements study, this graphical layout addresses what system administrators need to see, is faster and easier than analyzing text logs, and uses visualization techniques to effectively scale and display the data. With this design, we have built a tool that effectively uses operational alarm log data generated on the Georgia Tech campus network. The motivation and background of our design is presented along with examples that illustrate its usefulness.

Networked systems still suffer from poor firewall configuration and monitoring. VisualFirewall seeks to aid in the configuration of firewalls and monitoring of networks by providing four simultaneous views that display varying levels of detail and time-scales as well as correctly visualizing firewall reactions to individual packets. The four implemented views, real-time traffic, visual signature, statistics, and IDS alarm, provide the levels of detail and temporality that system administrators need to properly monitor their systems in a passive or an active manner. We have visualized several attacks, and we feel that even individuals unfamiliar with networking concepts can quickly distinguish between benign and malignant traffic patterns with a minimal amount of introduction.

Currently mobile IP can enable mobile users to enjoy seamless roaming. However, if home networks are firewall-protected, mobile users can not access their home networks without successful authentication. So mobile users are out of contact with their home agents and then get lost to some extent. In this paper, we consider the case that, in mobile IPv4, a mobile node away from home obtains a care-of address from a foreign agent and communicates with its home agent and a correspondent node that are both behind the firewall of the home network. Our solution can achieve successful firewall traversal as well as end-to-end security by applying IPsec mechanisms on network entities. It does not require any modification of protocols and network entities. Besides, if foreign agents are deployed hierarchically, the security associations do not need to be renegotiated whenever a mobile node changes its network attachment point.

As the cost of IEEE 802.11 hardware continues to fall, the appeal of inserting unauthorized wireless access into enterprise networks grows. These rogue access points (AP) expose the enterprise network to a barrage of security vulnerabilities in that they are typically connected to a network port behind the firewall. Most of the current approaches to detecting rogue AP are rudimentary and are easily evaded by hackers. We propose the use of temporal traffic characteristics to detect rogue AP at a central location. This detection is independent of the wireless technology (IEEE 802.11a, 802.11b, or 802.11g), is scalable, does not possess the inefficiencies of the current solutions, and is independent of the signal range of the rogue AP.

A scheme for enhancing the TCP performance when a handoff occurs within a heterogeneous mobile network is proposed. Currently, the research on the interworking between 3G cellular networks and a WLAN is actively being conducted. To integrate these two technologies, there are many issues such as the network architecture, mobility management, and security which should he solved. Implementing a seamless handoff between WLAN and 3G networks is an essential issue. In this paper, we present some issues to develop a network that supports interworking between WLANs and 3G cellular networks, especially focusing on the TCP challenges. We examine a TCP performance during an intersystem handoff between a WLAN and a 3G cellular network and discuss some problems that the current TCP experiences during intersystem handoff and propose some schemes to improve TCP performance.

We propose a deployable approach to improving QoS by using the familiar overlay architecture approach. The goals of this work are: (1) to create an overlay architecture which allows us to sample specific path quality metrics among different paths; (2) to utilize the proposed overlay architecture in order to implement our proposed QoS-based routing scheme, application layer switching (ALSW). We show that we are able to achieve better than best-effort QoS without modifying intermediate nodes (i.e., routers), thus encouraging immediate deployment. Additionally, this research is performed on an actual wide area network testbed, comprised of universities across the nation. Also, we assemble this architecture as a peer-to-peer framework, encouraging collaborating individuals with average workstations to improve the QoS of their traffic.

Current trends show that 3G cellular network and WLAN will coexist and work together to support more users with higher data rate services over a wider area. In this hybrid mobile network, the WLAN provides high bandwidth data service over a small area while the 3G cellular network provides a higher mobility with lower bandwidth data service. To provide seamless data service to mobile users, vertical handoff between WLAN and 3G cellular network has to be implemented. We present the challenges in the vertical handoff. We propose a TCP scheme for a seamless vertical handoff, and present a performance evaluation. In the proposed scheme, the TCP sender and receiver use the Handoff (HO) option field in TCP header to recognize an impending handoff and a completing handoff. After a vertical handoff, the sender tries to readjust its data rate, since the new network has drastically different characteristics in contrast with horizontal handoff where keeping the same data rate improves performance. The proposed scheme can be implemented incrementally. It is not necessary to change all of the TCP senders for compatibility since it uses an optional field in TCP header.

Popularity of the Internet and the availability of broadband links (e.g., xDSL and cable) to residential consumers have initiated a demand for high quality video streaming. In video-on-demand-like (VoD) applications, a server responds to a client's request by streaming a multimedia object. However, the delivered media quality is usually limited by the lowest-bandwidth link on the network path to the client. An approach that stores multi-rate (scalable) video sequence at a proxy can enhance the video quality and bandwidth efficiency. In this paper, we present bandwidth sensitive caching (BSC) strategy where variable-rate streams are cached into a proxy in order to maximize the perceived video signal quality. The proxy determines the optimum rate at which a video needs to be stored base on the client capabilities and network link characteristics. Simulation results show that the proposed BSC algorithm is adaptive and robust to change in delivery condition, yet it is still simple and efficient for deployment onto proxies.

On HFC cable networks, in order to develop a real-time game application, we face a design problem to efficiently transmit packets with reliability. This paper introduces the SCRA (server-based collision resolution and avoidance) scheme. SCRA is a reliable transport method using UDP for real-time applications on HFC networks. In this design, we first analyze the collision probability, and estimate the required throughput on an upstream contention channel. SCRA controls the packet delivery, de-correlates the traffic bursts, and maintains a stable throughput for the application. The simulation shows that SCRA achieves ideal transmission time and bandwidth utilization. We also give the formulae to derive the parameters for a specific real-time application using SCRA.

In this paper, we present an analysis of the collision resolution mechanism in the Home Phone-line Networking Alliance (Home PNA) 2.0 MAC protocol. We begin with a brief description of the collision resolution (CR) mechanism, bringing out the differences with respect to other CR mechanisms. We show that the mechanism can be modeled as a recursive one, with each CR cycle consisting of smaller CR cycles. This recursive model is then used to relate CR cycle periods with different variables in collision resolution. These relations form the basis of a numerical method to find the mean of CR cycle periods, as functions of initial collision multiplicity, the number of CR slots, and the priority class of traffic. Thus, having characterized the CR mechanism, we discuss how to operate it optimally, given the network conditions. We show that the choice of three slots for CR, as in the standard, is sub-optimal in many cases. We conclude with a proposal for a dynamic CR mechanism, in which the number of CR slots can be varied dynamically. Without going into the implementation details, we discuss how the analysis results can be used in this new mechanism.

All-optical switching or wavelength routing has the benefit of optical bypass that can eliminate expensive high-speed electronic processing at intermediate nodes and reduce significantly the cost of high-bandwidth transport. But all-optical switching has the limitations of coarse granularity, lack of multiplexing gain, and scarcity of wavelength resources, which do not mesh well with Internet traffic that has many small and diverse flows and emphasizes the importance of resource sharing. In particular, wavelength routed light paths have difficulty to seamlessly converge with multiprotocol label switching label-switched paths that have arbitrary bandwidth granularity and relatively abundant labels. In this paper, we propose a hybrid wavelength and subwavelength routing scheme that can preserve the benefits of optical bypass for large traffic flows at the same time provide multiplexing gain for small traffic flows. We first study the hybrid routing scheme using static optimization that produces an optimal path set and a partition between wavelength and subwavelength routing. We then present a dynamic heuristic that tracks the static optimization closely. During the process, we proposed a traffic arrival process called incremental arrival with sporadic random termination to more accurately model practical optical network traffic generation process.

Although wavelength routing has many advantages, it also has some inflexibilities. For one thing, the routing granularity is large, which could lead to waste of bandwidth when demand is fractional in the units of wavelengths. For another, full connectivity in a large network puts a serious stress on the number of wavelengths required in the network. To solve these problem, we propose a hybrid wavelength and sub-wavelength routing scheme, which provides, in addition to a set of dedicated wavelength channels where normal wavelength routing takes place, a pool of shared wavelength channels where sub-wavelength routing is performed. The hybrid scheme is designed to strike a right balance between the benefits of optical bypass and multiplexing gain. The problem involves optimal routing and traffic grooming in a mesh network. We formulated the problem in the hybrid scheme using integer linear programming, and studied its performance under different cost scenarios using a prototype network. Our result shows the hybrid scheme can invariably achieve lower total system cost, and is especially effective where the tension between the benefits of optical bypass and multiplexing gain is most intense. The proposed hybrid scheme provides a cost-effective and flexible way for network service providers to accommodate diverse customer bandwidth demand granularities, and offers a smooth migration path to integrate existing opaque network elements with newly introduced all-optical ones.

We consider the aggregation of link-state information for an asymmetric communication network that supports quality of service (QoS)-based routing. The common strategy used to improve routing scalability is to divide the network into multiple autonomous systems (AS). Only the aggregated link-state information is advertised among AS. Compared to the network reachability, the link-state information, such as the residual bandwidth used in computing QoS routes, changes frequently and it appears in simulations to be asymmetric. We focus on networks that employ rate-based service discipline schemes and map delay constraint into nodal rate guarantee as done with the guaranteed QoS proposed for the Internet; hence, we propose aggregation algorithms for link residual bandwidth, based on existing aggregation approaches of QoS-routing information, the full-mesh, star and spanning-tree approach. We evaluate the proposed algorithms with different traffic volumes and numbers of border nodes, based on simulations with a randomly-generated physical network. We compare these aggregation approaches in terms of their performance and scalability (the amount of link-state advertisement generated). Using our simulations, we provide heuristic solutions of achieving good performance and scalability for implementing inter-domain QoS routing. Our main results show that the spanning-tree approach with our aggregation algorithms could achieve similar performance to the full-mesh approach; both are superior to the star approach. The amount of generated advertisement traffic by the spanning-tree approach is less than that generated by the star approach or the full-mesh approach.

In an integrated network, QoS routing plays an essential role in supporting various classes with different priority and quality-of-service (QoS) characteristics. The path selection procedure is an important part of the QoS routing scheme. The existing path selection algorithms do not consider the class distribution information of residual bandwidth (RB-CDI). As a result, these algorithms may cause the sessions of higher priority classes to be preempted instead of those of lower priority classes. We propose a new and straightforward path selection algorithm to solve this problem. The proposed algorithm uses not only the information of residual bandwidth amount but also RB-CDI. We evaluate the proposed algorithm by comparing with existing path selection algorithms. The performance evaluations are done in various situations. We use the throughput of each class and the link utilization of the network as evaluation metrics.

In mid 1980s, congestion control algorithms were implemented in TCP, realizing that the original flow control mechanisms were not capable of protecting IP networks from severe congestion. In recent years, the limitations of endpoint congestion control have been realized. The active queue management method RED and the feedback scheme explicit congestion notification (ECN) have been proposed to complement the TCP congestion control with the goal of preventing congestion instead of curing the network after congestion occurred. We evaluate the performance of the RED/ECN congestion avoidance system, and show that it is not dynamic enough to provide successful congestion avoidance in different traffic conditions. As an alternative to random early setection (RED), we propose an adaptive queue management scheme that can maintain high throughput and low roundtrip delays under dynamic traffic loads.

In this paper, we are going to focusing on the scalability of routing advertisement schemes for establishing connections with on demand end-to-end QoS requirements. The correctness of QoS-based routing mainly depends on the accuracy of routing information such as link residual bandwidth. Advertising network resource availability could introduce the routing scalability problem, due to its frequent change. Within each routing area, each router needs to constantly advertise its resource availability information and this information is flooded into the entire routing domain. We investigate the trade-off between scalability and correctness of QoS routing. We consider periodic and dynamic (threshold and exponential-class) intra-domain QoS routing advertisement schemes combined with the use of a clamp down timer. We propose a simple "crankback with cache" scheme by modifying the traditional crankback, and compare their effects on different situations. We define a performance metric to reflect the correctness for each scheme. Our measurement aims to evaluate the correctness and scalability in the environment of inter-domain QoS routing. Using our simulations, we provide heuristic solutions of achieving good performance and scalability for implementing QoS routing.

A hybrid QoS aware SR-ARQ (HQSR-ARQ) is proposed to increase the network throughput for video delivery in a bandwidth limited and error prone wireless mobile environment with certain deterministic guarantees. HQSR-ARQ balanced the pros and the cons of the conventional SR-ARQ and FEC for error control. It also utilized the layer property of MPEG to provide more network resources for important data sections within a video stream. Comprehensive computer simulations were used to compare the performance of HQSR-ARQ with a conventional SR-ARQ and the original QSR-ARQ in terms of the same QoS matrix. The results demonstrated the effectiveness and performance improvement of HQSR-ARQ.

In future IP networks, nodes supporting new congestion avoidance mechanisms like RED and ECN are going to exist together with nodes carrying traditional drop tail buffers. We study the performance of a set of TCP flows passing through two congested nodes in such a heterogeneous network. Our results show that unequal hop behaviour (in the form of RED and drop tail) in the congestion points can increase the bias against TCP flows passing through multiple congested nodes. Parameter settings of RED become critical again in the dual-bottleneck situation just like in the single-bottleneck case. Furthermore, appropriate settings for single- and dual-bottleneck situations appear to be significantly different, making it more problematic for RED to provide a "better-than-drop tail" performance with a fixed set of parameters.

A multilevel resource allocation scheme is proposed to tackle the problem of how to flexibly allocate limited wireless network resources to high bandwidth demand video traffic with certain QoS guarantees. This scheme utilizes the resource allocation flexibility provided by a CDMA/TDD system and assigns available bandwidth to different traffic loads. The available bandwidth includes codes, time slots, and up/down channel capacity. A computer simulation system based on Ericsson's wideband packet-CDMA architecture has been developed. Multiple MPEG video traces are used to explore the system capacity. Moreover, an optimal smoothing technique is used to pre-process the video traces so that the bit-rate variability and the bandwidth requirement are reduced. The simulation results demonstrate the significant performance improvement.

This paper analyzes the trunking performance of ATM Adaptation Layer Type 2 (AAL2) for variable bit rate (VBR) voice transport. In order to transmit voice traffic over ATM networks, unstructured and structured circuit emulation services using AAL1 were proposed as possible standard-based methods. However, although AAL1 is offered as a standard-based solution by some ATM equipment manufacturers, it is not considered an optimum solution, in terms of bandwidth utilization efficiency, for voice transport due to the lack of support of multiple individual voice users per ATM connection, compression, and silence suppression. In order to satisfy the critical need in the market for voice-over-ATM, AAL2 is defined in the ITU-T Recommendation I.363.2 which is designed with the capabilities to support multiple voice users per ATM connection and transport compressed/silence-suppressed VBR voice traffic. In this paper, we conduct detailed quantitative analysis of the trunking performance of AAL2.

Asynchronous transfer mode (ATM) is designed to support various traffic classes. It is necessary to select a proper traffic class to support a specific application. Voice traffic in its inherent nature is time-sensitive and variable. Therefore, it is natural to consider voice as real-time VBR traffic. Human speech has a voice activity factor of about 42% on an average, which makes it possible to multiplex a lot of voice sources together. The study of cell loss is of great importance to the design of an ATM multiplexer whose input consists of voice sources. With a maximum delay allowed in the network, it is the behavior of cell loss, rather than the variation of network delay, that determines the quality of reconstructed voice at receivers. This paper analyzes the cell loss performance and multiplexing gain of an ATM multiplexer loaded with VBR voice sources, where multiple voice streams, utilizing compression and silence detection, are multiplexed into a fixed bandwidth circuit such as T1 or T3 ATU trunk. This paper shows that the cell loss ratio and multiplexing gain depend on the voice activity factor, the mean talk spurt length, the mean silence period, the link capacity, the compression ratio, and the buffer size of the ATM multiplexer.

The wireless medium is a s=ce shared resource in mobde computing.Consequently, the media access control (MAC) layer influences the fairness and robustness of the wireless network.According to the current MAC protocok, stations are not able to gain access equdy to the shared wireless medium.This problem is conunody known as the fairness problem.The fairness problem occurs mostly bemuse of the existence of hidden stations and the presumption of a non-Wy connected wird=s network topology.This paper addresses solutions to the fairness problem in wireless networks.persistent carrier sense mdtiple access based dg~ rithms are proposed in which a fair wirel=s access for each user is accomplished using a precsdtiated N acce~Probabfity, Pij, . .that represents the Eti access probabtity horn station i to j. Lii access probabfities are dcdated at the source station in two ways using connection-based and time-based media access methods.According to the used methods, each active user broadcasts information on either the number of Iogicd connections or the average cent ent ion time to the stations within the communication reach.This information exchange provides partird understanding of the topology of the network to the stations.Each station reserves a specific priority for itse~to gain access to the shared medium.It is suggested that the information is exchanged during the W access discovery procedure for the connection-based method, and periodidy for the time-based method.Link access probabtit ies are modified every time the exchanged information is received.The proposed algorithms are dynamic and sensitive to the changes in the network topology.The sdgoritb have been implemented in a specific media access control protocol [1], but they are app~mble to d media access control protocok.Simdation restits show that the algorithms restit in an order of magnitude performance improvement in terms of throughput in a wirel= network.

In this paper, we evaluate the performance of infrared communication methods using repetition-rate coding over L-PPM wireless links to provide reliable infrared transmission throughout indoor environments. All receivers adapt the communication data rate by monitoring the channel, and they instruct transmitters to use highest rate if it is possible. Reducing the user data rate by a factor of RR (rate reduction) results in an RR-fold SNR improvement. We analyze how repetition-rate coding improves the capture probability of the infrared modem over L-PPM links. We also discuss the effect of RR-fold transmission in utilization using go-back-N and selective reject ARQ schemes.

An adaptive technique is described for compressing data that are flowing through a communications channel, being transferred to and from a personal computer using a modem to connect to a remote computer or database service. The objective is to reduce the transmitted data to close to five bits for each character of input data in typical ASCII text files with an algorithm that is simple enough that an eight-bit microprocessor, such as a Z-80, can handle a 19200-b/s asynchronous channel and still be able to handle, in addition, X.25/LAPB error-control protocol functions. This allows the data to be transmitted from modem to modem at 9600 b/s with synchronous transmission using the fast-turnaround ping-pong protocol developed for the Hayes V-series 9600 modems, with the user connected to the modem at 19200 b/s. The technique described meets those objectives for most text files and for most Lotus worksheet files as well. Less effective compression is realized when more random data are transmitted, such as executable binary files; however, the compression ratio is always close to the theoretical limit given by information theory for character-by-character compression. As an example of the effectiveness of this technique, it reduced the ASCII text file of a draft of this paper from 10928 to 6583 bytes, or to 60% of the original size. This corresponds to 4.8 bits per character.>