This paper explores the complexities of designing a multi-element transceiver system for free-space optical (FSO) communication between unmanned aerial vehicles (UAVs). We formulate the problem of placing optoelectronic transmitters (TXs, e.g., lasers) and receivers (RXs, e.g., photodetectors (PDs)) on a transceiver plane. The formulation aims to maximize the Signal-to-Interference-plus-Noise Ratio (SINR) among two hovering UAVs. We prove that the optimum tiling of TX and RX elements on an in-band full-duplex (IBFD) transceiver is NP-complete. Using a genetic algorithm (GA), we investigate solutions to the optimum tiling problem for various transceiver shapes, including circular, hexagonal, rectangular, and square shapes. The optimum SINR does not occur at a fixed coverage ratio but instead varies non-monotonically with link range. For each transceiver shape, we find diverse tiling patterns until the grid size becomes equal to the beam footprint. Furthermore, we identify unique laser placement patterns for each transceiver shape that sustain optimal performance over varying link ranges. Despite the increasing number of TXs (28 at 40 m to 52 at 100 m for square shape transceiver), the GA finds the same optimized tiling geometry, allowing the design to scale across distances for multiple platforms without need for mechanical steering.

Underwater communication systems mostly use acoustic signals relayed from a buoy into the water. This approach avoids the high radio attenuation in the water but is limited to the narrow bandwidth of acoustic signals. Optical wireless communication (OWC) has emerged as a promising technology for high-speed underwater networking applications, including global climate monitoring, military operations, and marine biology research. Leveraging the unlicensed optical spectrum enables high data transmission rate. However, this approach faces challenges from absorption, scattering, and turbulence, particularly at the air-to-water (A2W) interface. The dynamic nature of water surfaces causes significant disruptions, compromising the stability and reliability of the end-to-end communication link. This study investigates the impact of water surface variations on the signal-to-noise ratio (SNR) and bit error rate (BER) at the underwater receiver in an A2W OWC channel when the transmitter is mounted on an unmanned aerial vehicle (UAV). A Monte Carlo–based ray propagation framework is adopted to model stochastic scattering effects, and the system performance is evaluated for two different configurations: a small-aperture receiver with lower transmit power and a large-aperture receiver with higher transmit power. We propose a movement optimization framework for the UAV. By dynamically adjusting its position, the UAV can compensate for signal degradation caused by variations in the water surface. We develop and evaluate three movement optimization strategies, tailored for performance, reliability, and value, and visualize the resulting UAV motion using streamplots. Furthermore, we analyze the influence of water surface and system parameters, such as water surface steepness and receiver depth, on different metrics of the UAV movement optimizations. Additionally, we analyze the overall SNR and BER performance by comparing these different optimization approaches. The findings demonstrate that adaptive UAV positioning significantly enhances communication performance, even in the presence of highly dynamic water surfaces.

Fifth-generation (5G) wireless networks harness the extensive spectrum available in the millimeter-wave (mmWave) frequency bands which set them apart from current wireless systems in terms of directivity, propagation loss, and susceptibility to blockages. Sub-6 GHz systems can attain omni-directional coverage, displaying limited sensitivity to physical obstacles. Still, they are incapable of achieving the same level of service quality as systems outfitted with electronically steerable directional antennas offering reduced propagation loss and higher gains due to the beam directionality. In our framework, we investigate the utilization of directional, steerable mmWave antennas as integral components. The nodes communicate by manipulating the orientation of their antennas, i.e., steering their beams. To minimize dependence on a base station, the nodes are categorized into primary antennas (PAs) and secondary antennas (SAs), and they communicate in three phases: Uplink (SA to PA), Downlink (PA to SA), and PA-PA. We delve into the impact of optimal steering of the main lobe beams transmitted by these antennas as well as optimizing the time sharing among three phases. Within each phase, we assume that the nodes follow a random transmission scheduling scheme and derive the achievable rates accordingly. Through meticulous design of polynomial-time heuristics, we maximize the overall network capacity.

Peering between Internet Service Providers (ISPs) is playing an increasingly critical role in Internet traffic exchange. As content delivery networks continue to expand, major content ISPs are increasingly opting for peering arrangements over transit services to facilitate faster exchange of traffic. The satisfaction of the ISP pair and the longevity of the peering arrangement depend on the stability and performance of these peering relationships. We introduce meta-peering, a term which refers to the set of tools needed to help and automate the ISP peering process – starting with identifying a list of ISPs that are likely to peer, writing router rules to establish BGP sessions with them, and extending the service to monitor all these sessions for notifying any major outages or peering agreement violations. In this paper, we first make a thorough analysis of recent trends in ISP peering and describe how meta-peering can be implemented by integrating some of the existing tools. We mainly focus on instrumenting the automation of the peer selection process with an aim to identifying potential peering partners and peering locations to exchange traffic. Using these direct peering links greatly reduces energy consumption as traffic takes much shorter paths to their destinations, going through reduced number of intermediary devices (e.g., routers, switches) compared to elongated transit routes, consequently reducing the environmental impact. Utilizing PeeringDB and CAIDA datasets to identify possible peering points for ISP pairs, we consider ISPs’ internal policies to generate a list of acceptable peering contracts (APCs). We design two methodologies to rank order each ISP in the APC list and offer guidance on which ones would be stable and beneficial for the potential peers. A study of more than 3,000 ISP pairs (mostly active in North America) shows that our peer selection methods can attain around 80% accuracy in predicting peering relations.

Millimeter-wave (mmWave) signals experience severe environmental path loss. To address this issue highly directional antennas with beamforming capabilities are used to align the transmit and receive antenna beams, allowing the signal to travel longer distances. However, advanced algorithms are needed to detect the angle-of-arrival (AoA) for better alignment of the antenna beams. Combining software-defined radios (SDR) with mmWave radio frequency (RF) antenna systems can enable researchers to develop advanced algorithms for real-world scenarios. Using low-cost mmWave RF front-end components and an SDR, we develop a testbed that uses open-source tools and high-level programming languages for beamforming algorithm development. In the testbed, we prototype a deep Q-network (DQN) algorithm for mmWave AoA detection. We evaluate the performance of the algorithm by fine tuning the reinforcement learning (RL) hyperparameters.

Low-Earth Orbit (LEO) satellite constellations are becoming a critical component of the global networking infrastructure. Integration of mesh networks of LEO satellites to the Internet and other mission-critical systems has the potential to revolutionize the global networking infrastructure. Routing traffic is a crucial need for the emerging LEO satellite networks to support communication between ground stations. In this paper, we propose a distributed routing mechanism, Two-Phase Geometric Routing (TPGR), that utilizes the geometry of the satellite constellation. TPGR splits the task of delivering a packet to its destination satellite into two phases: (1) Reaching the destination plane and (2) Reaching the destination satellite. This divide-and-conquer approach enables TPGR to handle all possible voids smaller than a hemisphere and all dead-ends, without any support from the Global Positioning System (GPS). On various Walker Delta satellite constellations, we compare TPGR to shortest-path routing and a simpler geometric routing mechanism. Our experiments show that TPGR attains path failure rates similar to shortest-path routing while incurring about 5ms additional latency on our baseline constellations with high inclinations and 2ms additional latency on the Starlink and Kuiper mega-constellations.

The field of underwater optical wireless communication (UOWC) has garnered significant attention due to its potential applications in global climate monitoring, military operations, and marine biology research. UOWC offers several advantages, including higher transmission data rates due to increased bandwidth utilization in unlicensed spectrum bands. However, it also faces challenges such as absorption, scattering, and turbulence, especially when dealing with the air-to-water (A2W) interface, which can be random and disruptive. This study involves simulations that demonstrate how a dynamic water surface disrupts the optical wireless communication channel between air and water in terms of received signal intensity. To address this issue, we explore the feasibility and advantages of optimizing the movements of an unmanned aerial vehicle (UAV) with an optical transmitter to counteract the interference caused by water surface waves. By simulating three optimized UAV movement strategies customized for value, reliability, and performance across both intermediate and deep water scenarios, this study demonstrates their effectiveness in achieving improved communication, even in the presence of a disruptive water surface.

Directional antenna systems are gaining widespread adoption in wireless communication solutions, particularly using super-6 GHz bands in the electromagnetic spectrum. Hence, neighbor discovery and beam alignment in these directional wireless systems have attracted notable attention from researchers. However, fast neighbor discovery using directional wireless while maintaining covertness from eavesdroppers by minimizing the probability-of-intercept (POI) is an open research problem. We address this trade-off by proposing a sequential transceiver (or direction) selection protocol based on a tuning parameter (α) that guides the nodes to prioritize either goal by selecting the next operational transceiver subset for probing. We consider a 2-D multi-sector directional wireless system with electronic steering of transmission among sectors, assuming each sector is equipped with a transceiver and the sectors collectively cover the 2-D 360°horizon around the node. We design a time-slotted neighbor discovery protocol that employs a probabilistic approach to select only one transceiver to use for the next time interval. By changing α, we study its capability to control the probing direction and impact on neighbor discovery speed and POI. Results show random selection offers fastest neighbor discovery but increases vulnerability to passive eavesdropping. Choosing from transceivers placed opposite to the active one accelerates discovery, while prioritizing the adjacent ones enhances covertness. During the search for the best α, we observe that exclusively prioritizing either rapid discovery or minimizing POI for a long stretch does not yield an optimal solution.

Immersive Virtual Reality (VR) applications demand low network latency, large bandwidth, and substantial computational resources. Despite significant progress in addressing these challenges, creating Distributed VR environments remains complex. Existing VR deployments are predominantly centralized. Extending VR to a distributed setup requires solving scalability challenges of the network support needed for VR servers distributed across a network. In particular, the scale of traffic between distributed VR servers and the interaction of this VR traffic's size with various features of the VR applications are unexplored. In this study, we present and evaluate a distributed multi-server VR environment based on Mozilla's popular open-source platform, Hubs, on a local area network (LAN). By conducting traffic measurements, we evaluate how the network traffic volume to support such distributed VR setups may evolve. Our work assesses the feasibility of creating such distributed VR environments. We find that the inter-server traffic exhibits logarithmic increase with respect to the client count when the clients make human-like movements, pointing to the scalability potential of Distributed VR environments. Additionally, the study lays the foundation for future optimizations, aiming to enhance the distributed VR experience for users.

We analyze traffic exchange between Internet Service Providers (ISPs) at an Internet Exchange Point (IXP) as a non-cooperative game with ISPs as self-interested agents. Each ISP has the choice of exchanging traffic either using the shared IXP facilities, or outside the IXP – through their transit providers or private peering. We analyze the efficiency (social cost optimality) of the traffic exchange equilibrium at the IXP taking into consideration the congestion cost experienced by the ISPs at the IXP. To model both non-profit and for profit IXPs, we consider several cases, i) where the IXP does not charge any price to ISPs for the traffic exchanged (zero pricing), ii) when it charges a price that is proportional to the aggregate level of congestion at the IXP (proportional pricing), and iii) when it charges a constant price per unit traffic (constant pricing). Further, we also analyze the profit earned by the IXP under these pricing policies, under two different models of the congestion cost (delay) functions. Simulations conducted using data for actual IXPs obtained from PeeringDB demonstrate that the theoretical bounds derived for social cost and profit optimality at equilibrium (measured as the Price of Anarchy) are fairly tight, and correctly capture the performance trends against the variation of key model parameters. Further, the results show that for proportional pricing, there is an operating price range that attains near-optimal social cost and near-optimal IXP profitsimultaneously. We also demonstrate -through both theoretical analysis and simulations -that as compared to zero and constant pricing policies, proportional pricing attains better tradeoff between social cost and IXP profit, and also results in a performance that is more robust to price variations.

Attaining higher speed data communication from underwater to airborne platforms is of high interest for a variety of applications. Existing solutions are cumbersome, involving buoys at the water surface. Direct wireless communication from underwater to an airborne platform using optical beams would resolve several practical issues and potentially enable new wireless applications. We studied the propagation of Gaussian coherent beams from an underwater laser transmitter to a receiver in the open air in the presence of gravity-generated water waves at deep ocean levels. We modeled the emission of coherent Gaussian beams in the presence of third-order Stokes water surface waves. Further, we explored the relationship between beam propagation and turbulence caused by the water waves. The effect of the water wave's steepness and the divergence angle of the underwater laser on the amount of received power was investigated, as well as the link's availability, link power capacity, and survivor analysis of the power collected at the receiver.

Evident by the Federal Communications Commission’s (FCC) incorporation of a light leasing approach, high utilization of the Citizens Broadband Radio Service (CBRS) spectrum can be achieved by the commercial Priority Access License (PAL) operators sharing resources with unlicensed General Authorized Access (GAA) users. However, proper integration of PAL operators and GAA users into this new three-tiered CBRS spectrum sharing market is an open issue. This work introduces a collaborative GAA-clustered framework to facilitate such integration. We propose GAA users form multiple distinct geographical clusters and utilize the CBRS spectrum collaboratively rather than through individual access requests. Each cluster will nominate a central entity called the GAA leader, who will directly communicate with the PAL operators regarding CBRS spectrum access and set up the necessary PAL-GAA connections. Such direct communication will reduce the messaging overhead between the central CBRS Spectrum Access System (SAS) and the users across PAL and GAA levels, providing a reliable and convenient spectrum-sharing platform. Here, we propose a novel leader selection algorithm (LSA) that uses a GAA user’s network density and perceived signal strength to assign a Leader Evaluation Score (LES) to evaluate and nominate the GAA user with the highest score as the cluster leader.

The Federal Communications Commission (FCC) recently deployed the Citizens Broadband Radio Service (CBRS), a three-tiered spectrum-sharing approach that allows incumbent federal users to share the 3,550-3,700 MHz band with commercial users. In addition, the FCC also aims to encourage licensed providers, called the Priority Access License (PAL), to lease/share their licensed spectrum with unlicensed users, named the General Authorized Access (GAA), for a limited duration, by adopting a light leasing approach. In this paper, we aim to facilitate PAL-GAA collaborative spectrum access by proposing a novel clustered framework where the GAA users are grouped into multiple distinct geographical clusters and request access to the CBRS spectrum resources through the clusters collaboratively rather than individually. This process reduces the control messaging overhead between the CBRS controller and licensed and unlicensed entities, providing a convenient platform for licensed spectrum sharing. Also, submitting aggregated requests from multiple users rather than individuals will allow PAL operators to estimate the data traffic that their network may experience due to sharing. Later, PALs can make arrangements to allocate appropriate spectrum resources for sharing to the GAA layer. Finally, to encourage PALs to share, we also propose a government incentive model where PALs are allotted additional bandwidth for a limited span to be used as an extension to their licensed spectrum based on their level of sharing.

Data centers are embracing the software-defined networking (SDN) as it is evident that this technology of completely separating the data plane from the control plane gives more flexibility for their internal routing management and provides better Quality-of-Service (QoS) to the users. Implementing a similar solution to serve the purpose of software-defined wide-area networking using public Internet routing is also gaining popularity. Although, instead of having a complete separation, a hybrid approach to keep most of the control plane along with the least of the data plane in the remote and vice-versa for the local platform may be more fitting. To this end, we propose a new hybrid SDN approach, Cloud-Assisted Routing (CAR), that utilizes the high computational services that cloud offers at a lower price by splitting both control and data plane functions between a local router and a remote cloud computing platform. Such delegation of data plane to a third-party authority requires proper control plane management policies and handling or avoiding possible loops and failures. We detail the architectural view of CAR, address its associated challenges, and present prototype-based evaluations of it for reducing routing table sizes.

Dense Visible Light Communication (VLC) networks may offer a cost-effective solution to meet the growing demand for wireless data as legacy radio frequency (RF) bands are getting crowded. In this paper, we present a detailed analytical model and link performance analysis for dense multi-element VLC networks in the presence of spatial and temporal optical interference caused by multiple transmitters broadcasting data over a Multi-Input Single-Output VLC channel. In dense VLC networks, we investigate how the spatial interference caused by cross-talk degrades the link performance and calculate the Bit Error Rate of the link to determine the maximum data rate capacity of the channel for reliable communications.

The importance of peering in traffic exchange be-tween ISPs is rapidly increasing. With continuing growth in content delivery networks, large content ISPs are becoming increasingly inclined to exchange traffic through peering rela-tionships rather than using transit services. The stability and performance of these peering relationships dictate the satisfaction of the ISP pair and the durability of the peering. Quantification of various parameters that indicate the efficiency of peering contracts is however difficult. From the perspective of any ISP pair, there are two key decisions to be made: whether to peer or not, and at which location(s) to peer. We propose two metrics, peering willingness and peering stability, towards quantifying an ISP’s decision to peer at a location with another ISP, and the stability of that relationship. We compute these metrics using publicly available data to characterize peering relationships for different ISP pair types. We observe that peering between Content and Access ISP pairs results in the most stable and efficient relationship.

We present a disconnection tolerant routing protocol, Binary State Distance Vector Routing (BSDVR), that can provide unicast routing on partitioned networks. BSDVR introduces binary state information for distance vector (DV) entries to compute unicast paths even if the network is partitioned. We compare BSDVR against the traditional DV routing (TDVR) in a controlled network. Our experiments confirm that BSDVR generates more control overhead during single link failures that do not cause partitions. In terms of partition-causing link failures, BSDVR’s control overhead is less than TDVR’s by an order of magnitude, leading to much better convergence times.

The Internet landscape is progressively transitioning towards a flat hierarchical model to prune multiple Internet Service Provider (ISP) tiers. At the core of this transition is settlement free peering, which plays a critical role in mediating traffic exchange among ISPs. It is pertinent to take a closer look at peering and accurately emulate their operative model into a computation model that enables a concrete characterization without losing generality. In this paper, we utilize publicly available data-sets to identify the importance of several factors that play role in the peering process. We conduct a detailed analysis on the relationship of ISPs and their motivation behind selecting a peer ISP and use these findings to develop a Machine Learning (ML) based model that identifies feasible peering relationships. Preliminary results show a high correlation to the ground truth.

In communication networks, the usage of multiple-input multiple-output (MIMO) systems may give advantages such as enhanced rates or diversity. This article investigates the performance of blind signal separation and symbol detection under the assumption of unavailable receiver information and the absence of a training sequence to aid in detection. The Constant Modulus Adaptive (CMA) method is assessed as the foundation technique for discussing blind source recovery in MIMO systems, demonstrating its powerful capabilities in source recovery without a training sequence. The performance and convergence speed of the Multi-Modulus Adaptive (MMA) algorithm are then compared to the CMA algorithm’s low efficiency in recovering Quadrature Amplitude Modulation (QAM) signals. The Simplified Constant Modulus Adaptive (SCMA) algorithm’s performance in MIMO structures with low computational complexity and a reasonable efficiency in signal estimation is further investigated as a well-known solution to reduce the computational complexity of CMA and MMA algorithms in MIMO systems with a large number of receiving antennas. Finally, using the Cross Correlation Simplified Constant Modulus Adaptive (CC-SCMA) algorithm, the non-uniqueness of the signals recovered by CMA, MMA, and SCMA algorithms is addressed.

In this paper, we consider a device-to-device (D2D) millimeter Wave (mmWave) network that allocates a spectrum band with bandwidth BcHz exclusively to support communication of N cooperative D2D pairs over Rayleigh fading channels. The available bandwidth is divided into Ncnon-overlapping sub-bands. Each node is equipped with a directional antenna that is capable of steering its beam within its field of view. Also, each transmitter can adjust its transmit power. Aiming at maximizing the network throughput, the cooperative D2D pairs form Ncdisjoint coalitions, where the D2D pairs in a particular coalition share the same sub-band for communication and hence cause co-channel interference. We address this question: What is the best coalition among the D2D pairs, the optimal beams steering angles of directional antennas of the D2D pairs within each coalition, and the optimal transmit powers such that the network throughput is maximized? We formulate the network throughput maximization problem, subject to certain constraints, and we propose an iterative method, based on the block coordinate descent (BCD) algorithm, to solve the constrained optimization problem. Specially, we propose a coalitional game approach for coalition formation among the D2D pairs. We numerically investigate the effects of different system parameters (e.g., N, Nc, the antenna gain, the maximum allowed total transmit power), as well as the impact of optimizing coalition formation only, and optimizing transmit power only, on the network throughput maximization.

Visible Light Communication (VLC) is a rapidly growing technology which can supplement the current radio-frequency (RF) based wireless communication systems. VLC can play a huge part in solving the ever-increasing problem of spectrum scarcity because of the growing availability of Light Emitting Diodes (LEDs). One of the biggest advantages of VLC over other communication systems is that it can provide illumination and data communication simultaneously without needing any extra deployment. Although it is essential to provide data rate at a blazing speed to all the users nowadays, maintaining a satisfactory level in the distribution of lighting is also important. In this paper, we present a novel approach of using mirrors to enhance the illumination uniformity and throughput of an indoor multi-element VLC system architecture. In this approach, we improve the Signal-to-Interference plus Noise Ratio (SINR) of the system and overall illumination uniformity of the room by redirecting the reflected LED beams on the walls to darker spots with the use of mirrors. We formulate a joint optimization problem focusing on maximization of the SINR while maintaining a reasonable illumination uniformity across the room. We propose a two-stage solution of the optimization problem: design solution and communication solution. In the design optimization, we formulate an equivalent binary linear optimization to achieve the best illumination quality by optimizing the mirror placements and the LEDs’ transmit powers. In the communication problem, however, we aim to improve the throughput of the system using a fair utility metric based on maximizing the minimum user’s data rate. Due to non-convexity of the communication problem, we propose three different heuristic solutions and analyze their performance. We also show that about threefold increase in average illumination and fourfold increase in average throughput can be achieved when the mirror placement is applied which is a significant performance improvement.

Cell tower locations are not publicly available due to business interests of wireless providers. Very often wireless providers provide exaggerated coverage maps that may mislead the public. In addition to providing a neutral check on the coverage maps, prediction of cell tower locations hosting multiple operators’ access nodes could also be helpful in disaster communications and public safety in general. The localization of the disaster-affected towers can be very conducive to respond and reach to the victims. Further, victims’ devices could utilize this knowledge to initiate device-to-device (D2D) or unmanned aerial vehicular (UAV) communications as alternatives to the damaged cellular infrastructure. Publicly available crowdsourced cell (base station) locations and FCC’s sites can be used to predict the cell tower/site locations in the United States. In this work, we utilized a weighted k-means algorithm to predict cell tower locations from OpenCellid crowdsourced dataset and implemented a mapping algorithm to locate nearest physical towers. We map the predicted towers to two different sources of physical towers. Our comparison shows a significant accuracy in predicting tower locations regardless of sources of physical towers. The technique can be used to predict the tower locations in other countries as well.

In this paper, we propose a novel optimization model for multiple Unmanned Aerial Vehicles (UAVs) working simultaneously as relays to help two set of ground users; namely relay users and device-to-device (D2D) users. The relay users are assumed out communication rages from each other and use the UAV link to for their data transmission. While the D2D users are assumed to be nearby users and use the UAV for managing the resources without being involved in the transmission. The goal of the paper is to operate the UAVs in an energy-efficient manner to support the different set of users by i) optimizing the available bandwidth and power allocations of the D2D links, and ii) acting as relays when needed to maintain the communication links between relay users. We formulate an optimization problem that maximizes the throughput-energy utility while respecting the resource availability including the UAVs’ energy consumption, UAV-user association, and trajectory constraints. Due to the non-convexity of the problem, we propose to solve it in three steps using Taylor series approximation. Firstly, we optimize the transmit power of the UAVs and users. Then, we optimize the bandwidth allocation for a given transmit power values. Finally, an efficient heuristic algorithm based on a recursive shrink-and-realign process is proposed to optimize the UAVs’ trajectories. The performance of the proposed method shows advantages in terms of average throughput compared to the fixed power and bandwidth solutions.

One of the key problems in mobile crowdsensing (MCS) systems is the assignment of tasks to users. Most of the existing work aim to maximize a predefined system utility (e.g., quality of service or sensing), however, users (i.e., task requesters and performers/workers) may value different parameters and hence find an assignment unsatisfying if it is produced disregarding these parameters that define their preferences. While several studies utilize incentive mechanisms to motivate user participation in different ways, they do not take individual user preferences into account either. To address this issue, we leverageStable Matching Theorywhich can help obtain a satisfying matching between two groups of entities based on their preferences. However, the existing approaches to find stable matchings do not work in MCS systems due to the many-to-one nature of task assignments and the budget constraints of task requesters. Thus, we first define two different stability conditions for user happiness in MCS systems. Then, we propose three efficient stable task assignment algorithms and discuss their stability guarantees in four different MCS scenarios. Finally, we evaluate the performance of the proposed algorithms through extensive simulations using a real dataset, and show that they outperform the state-of-the-art solutions.

Primary-secondary spectrum sharing is limited in terms of design space, and may not be sufficient to meet the ever-increasing demand of connectivity and high signal quality. The next step to increase spectrum sharing efficiency is to design markets where sharing takes place among primary providers rather than leaving it to the limited case where the primary licensee is idle. Attaining contractual spectrum sharing among primary providers, a.k.a. co-primary or inter-provider sharing, involves additional costs for the users, e.g., roaming fee. Co-primary spectrum sharing without additional charge to the users poses two major challenges: a) regulatory approaches must be introduced to incentivize providers to share spectrum resources, and b) small providers in co-primary spectrum sharing markets may freeride on large providers' networks as the customers of the small providers may be using the spectrum and infrastructure resources of large providers. Such freeriding opportunities must be minimized to realize the benefits of primary-level sharing. We consider a subsidy-based spectrum sharing (SBSS) market to facilitate co-primary spectrum sharing where providers are explicitly incentivized to share spectrum resources. We focus on minimizing freeriding in SBSS markets and introduce a game-theoretic model to regulate the freeriding. We use the model to explore operational regimes with minimal freeriding.

Device-to-device (D2D) links enable direct communication between mobile devices without using the cellular network or the Internet. This type of communication can be helpful in situations when there is a partial or complete failure of the network infrastructure. However, effective use of D2D links for a multi-hop D2D communication system requires quick and practical quantification of their quality from user space of devices. We developed an Android application to search and measure the quality of available D2D links nearby. This application can search for heterogeneous (i.e., Bluetooth and WiFi Direct) D2D links simultaneously and measure the link quality from the user space. We run indoor and outdoor experiments to examine how line-of-sight or non-line-of-sight D2D links perform.

With the rapid growth of the Internet traffic and the intensity of online transactions taking place, it is expected that the current routing needs careful modifications and smart innovations to ensure effective and reliable end-to-end packet delivery. This involves new feature developments for handling traffic with reduced latency to tackle routing scalability issues in a more secure way and to offer new services at cheaper cost. Considering the fact that prices of DRAM (Dynamic Random Access Memory) or TCAM (Ternary Content-Addressable Memory) in legacy routers are not necessarily decreasing at a desired pace, cloud computing can be a great solution to manage the increasing computation and memory complexity of routing functions in a centralized manner with optimized expenses. Such cloud integration to routing is becoming plausible as cloud providers now offer various pricing schemes and provide large-scale computing infrastructure to meet the users' choice. Focusing on the attributes associated with existing routing cost models and by exploring a hybrid approach to SDN, we compare recent trends in cloud pricing (for both storage and service) to evaluate whether it would be economically beneficial to integrate cloud services with legacy routing for improved cost-efficiency.

Establishing highly reliable optical wireless communication links to submerged receivers exposed to insufficient light requires highly sensitive receivers with the ability to detect each photon carrying information. To this end, single photon avalanche diode (SPAD) receivers can be considered an appropriate option for the optical receiver system as they benefit from active quenching and biasing circuits, and offer a considerably high breaking voltage, providing the optical system with the ability to detect every single received photon in the ideal case. However, the sensitivity and bandwidth of the existing SPAD receivers have been limited by their dead time and limited photon detection efficiency. In this study, the performance of underwater SPAD receivers in detecting transmitted information from an optical transmitter located in the free space above the sea surface was assessed. To this end, the saddle-point approximation was used along with the Birnbaum-Saunders distribution to statistically model the fading coefficient of the air-to-water optical wireless communication channels and the statistical photon counting behavior of SPADs. The performance of the communication link was then assessed by obtaining the analytical relations for bit error rate. Finally, the results of numerical simulations are presented and the negative effects of dead time on information detection in the optical receiver system in various transmission bit rates are studied.

To enable visible light communication (VLC) for mobile receivers, we design and prototype a wide field-of-view (FOV) optical receiver with off-the-shelf components and in forms that are conformal to the receivers' surface. The VLC system uses high-efficiency optical transmitters with high brightness (7645 Lux in 1 m) low power (36 W) white LED panels which also provide proper lighting. To overcome the detrimental effects of the time-varying inter-symbol interference (ISI) due to the VLC receiver's high acceptance angle and vibration in its structure, we design and utilize an optimal multiple-symbol detection (MSD) algorithm. MSD attains remarkable improvements compared to the symbol-by-symbol detection but with exponential time cost. To decrease the MSD's computing demands, we then design an adaptive Decision Feedback Affine Projection Algorithm (DF-APA). DF-APA attains a notable further improvement with polynomial computation complexity which allows faster response to VLC channel dynamics. We, finally, test the system in presence of intense vibration in the receiver's body and show a 20 Mbps VLC link over 7 m distance.

SDN is based on the idea of a centralized controller with a global view of the network topology. However, in large networks, multiple controllers work together to perform global network functions. This presents challenges in load balancing, consistent network view, and controller placement for scalability and reliability. When multiple controllers reside in different domains, their communication challenges are increased as each may have its own security and access policies. We present a reactive distributed SDN application built as a custom module in Floodlight that allows multiple controllers to make joint decisions where the controllers reside in different domains by communicating with an external server for information about participating organizations. Such a framework would be useful, for example, for providing access to patient information distributed among different hospital networks, big data sets between research institutions, or public safety data sets during disaster or emergency. The resulting approach will allow the SDN application layer to handle inter-domain traffic and enable data access between different organizations/agencies while respecting their different respective policies.

Effective communication among first responders during and in the aftermath of a disaster can affect outcomes dramatically. We seek to build a resilient architecture that allows first responders to communicate even with: 1) damage to infrastructure - civilian and / or specialized communication facilities may be damaged by the disaster, and 2) dynamically formed groups - first responder teams may be formed dynamically in response to a disaster and team member addresses (e.g., phone numbers, network addresses) may not be known to one another. We propose a resilient network architecture that allows efficient communication among first responders during and after a disaster [1]. We seek to support dynamically formed groups for incident response, allowing first responders to securely and conveniently communicate based on roles (names). The architecture supports communication in disasters by 1) building resilience into the framework across all the layers, 2) creating a framework that allows communication by role and identity, rather than addresses, 3) supporting multiple modalities (data, voice) for communication among dynamically formed first responder teams, and 4) providing robust and resilient communication and computing even when facilities are error- and disruption-prone.

In the modern day, there is a serious spectrum crunch in the legacy radio frequency (RF) band, for which visible light communication (VLC) can be a promising option. VLC is a short-range wireless communication variant which uses the visible light spectrum. In this paper, we are using a VLC-based architecture for providing scalable communications to Internet-of-Things (IoT) devices where a multi-element hemispherical bulb is used that can transmit data streams from multiple light emitting diode (LED) boards. The essence of this architecture is that it uses a Line-of-Sight (LoS) alignment protocol that handles the handoff issue created by the movement of receivers inside a room. We start by proposing an optimization problem aiming to minimize the total consumed energy emitted by each LED taking into consideration the LEDs’ power budget, users’ perceived quality-of-service, LED-user associations, and illumination uniformity constraints. Then, because of the non-convexity of the problem, we propose to solve it in two stages: (1) We design an efficient algorithm for LED-user association for fixed LED powers, and (2) using the LED-user association, we find an approximate solution based on Taylor series to optimize the LEDs’ power. We devise a heuristic solution based on this approach. Finally, we illustrate the performance of our method via simulations.

Directional Radio Frequency (RF) / Free-Space-Optical (FSO) transceivers have the potential to play a significant role in future generation wireless networks. They are advantageous in terms of improved spectrum utilization, higher data transfer rate, and lower probability of interception from unwanted sources. Despite these advantages, communications using directional transceivers require establishment and maintenance of line-of-sight (LOS). Thus, establishment of the communication link or neighbor discovery plays an important role in mobile ad hoc networks with RF/FSO directional transceivers. We consider two nodes (Unmanned Aerial Vehicles (UAVs) or quadcopters) hovering in 3D space, each with one directional transceiver mounted on a mechanically steerable spherical structure/head, with which they can scan 360 degrees in the horizontal plane and 360 degrees in the vertical plane. We propose a novel scheme that deals with the problem of automatic discovery and establishment of LOS alignment between these nodes. We performed extensive simulations to show the effectiveness of the proposed neighbor discovery method. We also developed a proof-of-concept prototype and conducted experiments with it. The results obtained from both simulations and experiments show that, using such mechanically steerable directional transceivers, it is possible to establish communication links to similar neighboring nodes within several seconds without using GPS support.

Internet Service Providers (ISPs) have different growth or decline patterns in terms of topological and economic characteristics. While some ISPs may have a significant correlation between their topological and business properties, others may not show such strong techno-economic dependence. In this paper, we examine the relationship between the network topology characteristics of the ISPs and their stock market values. We analyze data collected from two different datasets of inter-ISP relationships of various types, i.e., customer, provider and peer. Then, we correlate these topological relationships against the ISPs performance on the stock market. In particular, we examine the correlation between the stock market values as well as revenue of each major ISPs operating in the United States to their degree (i.e., the number of connections they have to other Autonomous Systems) and customer cone size (i.e., the number of customers they are serving).

Free-Space-Optical (FSO) communication has become an attractive option over Radio Frequency (RF) communication due to having broader bandwidth, unlicensed band, higher spatial reuse, and enhanced security. In-band full-duplex FSO (IBFD-FSO) transceivers ensure, in some cases enhance, these features enabling future vision of smart communication and Internet-of-Things (IoT) applications. Even though IBFDFSO transceivers can double the network capacity theoretically, overall performance and capacity is limited by interference and optical feedback. In this paper, we present a proof-ofconcept prototype of IBFD-FSO transceiver by implementing isolation technique to reduce optical feedback. We demonstrate the effectiveness of the isolation technique and performance through test-bed experiments using off-the-shelf components.

Traditional means for contacting emergency responders depend critically on the availability of the 911 service to request help. Large-scale natural disasters such as hurricanes and earthquakes often result in overloading and sometimes failure of communication facilities. Affected citizens are increasingly using social media to obtain and disseminate information. Social media is not only being used to communicate with first responders but also for people to organically volunteer and seek help from each other, complementing the role of first responders. In this paper, we examine the use of Twitter during two major hurricanes in the U.S. in 2017. We find that there exists a sizable number of people with access to the Internet even in areas where 911 services were down, and they tweet disaster-related information including requests for help. Our analysis indicates that social media can potentially help in disaster management and improve outcomes.

Visible light communications (VLCs) are a promising technology to address the spectrum crunch problem in radio frequency networks. A major advantage of VLC networks is that they can use the existing lighting infrastructure in indoor environments, which may have large number of LEDs for illumination. While LEDs used for lighting typically have limited bandwidth, presence of many LEDs can be exploited for indoor VLC networks, to serve each user by multiple LEDs for improving link quality and throughput. In this paper, LEDs are grouped and assigned to the users based on received signal strength from each LED, for which different solutions are proposed to achieve maximum throughput, proportional fairness, and quality of service. Additionally, power optimization of LEDs for a given assignment is investigated, and the Jacobian and Hessian matrices of the corresponding optimization problem are derived. Moreover, for multi-element receivers with LED grouping at the transmitter, an improved optimal combining method is proposed. This method suppresses interference caused by simultaneous data transfer of LEDs and improves the overall signal-to-interference-plus-noise-ratio by 2-5 dB. Lastly, an efficient calculation of channel response is presented to simulate multipath VLC channel with low computational complexity.

Terrorist organizations have social networks that enable them to recruit and operate around the world. This paper presents a novel computational framework for derivation of optimal destabilization strategies against dynamic social networks of terrorists. We develop a game-theoretic model to capture the distributed and complex dynamics of terrorist organizations, and introduce a technique for estimation of such dynamics from incomplete snapshots of target networks. Furthermore, we propose a mechanism for devising the optimal sequence of actions that drive the internal dynamics of targeted organizations towards an arbitrary state of instability. The performance of this framework is evaluated on a model of the Al-Qaeda network in 2001, verifying the efficacy of our proposals for counter-terrorism applications.

Free-Space-Optical (FSO) communication has the potential to provide optical-level wireless communication speeds. It can also help solve the wireless capacity problem experienced by the traditional RF-based technologies. Despite its capacity advantages, FSO communication is prone to mobility. Since the FSO transceivers are highly directional, they require establishment and maintenance of line-of-sight (LOS) between each other. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degree. We propose a novel scheme that deals with the problem of automatic maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. We design protocols to maintain an FSO link between the mobiles satisfying a minimum received power or signal-to-noise ratio (SNR). We also present a prototype implementation of such mobile node with FSO transceivers. The effectiveness of the alignment protocol is evaluated by analyzing the results obtained from both simulations and also experiments conducted using the prototype. The results show that, by using such mechanically steerable transceivers and a simple auto-alignment mechanism, it is possible to maintain optical wireless links in a mobile setting with nominal disruption.

Wireless devices with diverse capabilities are ubiquitous and will continue to flourish for the next foreseeable future. With cellular connectivity, each devicd is capable to utilize more necessary services. However, in some cases (e.g., public safety and disaster recovery) cellular connectivity may become unavailable. In these situations, device-to-device (D2D) communication can contribute to maintain connectivity as well as providing other services in terms of service sharing (e.g., SMS, Internet, camera) available in individual devices. This paper describes an approach where users can share wireless services with other users in a seamless manner. We develop a smart phone application, D2DMesh, for service sharing in a D2D manner. By using D2DMesh, users can get more work done via sharing, increase the spectrum utilization, create their own private networks without a centralized infrastructure and offload network traffic to a less congested network path. Our approach is platform-independent and is entirely implemented in user space. It allows sharing of services among neighboring devices over multiple hops without any help from the device vendors. We present results from initial experiments and show the effects of various important parameters on the performance of D2D service sharing.

In this study, we investigate angle-of-arrival (AOA) and received signal strength (RSS) based localization methods for visible light communication (VLC) systems. We show that while AOA-based localization allows the receiver to locate itself via a least squares estimator by exploiting the directionality of light-emitting diodes (LEDs), RSS-based approach takes Lambertian pattern of LEDs into account and better deals with further improving the localization accuracy via a nonlinear least squares (NLS) estimator. In order to reduce the complexity of the NLS estimator, we develop an analytical learning rule based on the Newton-Raphson method and use the result of AOA-based localization as an initial point for the learning rule. As a benchmark, we also derive generic analytical expressions of the Cramer-Rao lower bound (CRLB) for RSS-based localization.

End-to-end traffic engineering (E2E TE) in multi-hop wireless networks is hard since the nodes are dynamic and can fail or move. As the network size grows, the dynamism of the nodes prohibits E2E TE approaches using paths as well as network state defined using highly variant nodes and links. Thus, E2E TE over such dynamic networks require the capability of expressing E2E paths and network state in a manner independent of the nodes. We propose a roadmap-based trajectory planning scheme to perform E2E TE over multi-hop wireless networks. We illustrate how our roadmap-based approach can automate the process of planning/selecting the trajectories so that better balancing of the traffic is achieved. We compare our roadmap-based approach to its shortest-path routing counterpart, Greedy Parameter Stateless Routing (GPSR), and show that beneficial tradeoffs can be attained.

Free-Space-Optical (FSO) communication has the potential to not only deliver wireless communication links at optical-level speeds but also solve the wireless capacity problem that the traditional RF based technologies are confronting. Despite its advantages, FSO communication is prone to mobility. The highly directional FSO transceivers require establishment and maintenance of line-of-sight (LOS) between them. Facilitating continuous alignment requirements has been a major concentration of mobile FSO research to date. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degrees. We propose a novel scheme that deals with the problem of automatic detection, establishment and maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. The proposed method shows that using such mechanically steerable transceivers and a simple autoalignment mechanism, it is possible to maintain optical wireless links in a mobile setting with nominal disruption.

Demand for wireless data has increased significantly with the adoption of smartphones. To satisfy this huge demand, mobile operators are investing money and upgrading their infrastructure from 3G to 4G. However, it is expected that the demand will always stay hungry for more capacity and energy. This demand drives the need for alternate and complementary technologies in wireless communication. Free-space-optical (FSO) communication has the potential to serve as a complementary technology to RF for the future wireless networking. As a promising approach, multi-element spherical modules covered with multiple highly directional FSO transceivers has been shown to work well to handle mobility for FSO communication. Among other issues, the directionality of FSO communication necessitates a key problem to be solved in such modules: Maintaining the line-of-sight (LOS) among the mobile modules during an ongoing transmission. For FSO modules with many transceivers, reducing the modules' energy consumption becomes a crucial issue for the practicality multi-element FSO designs targeting mobile and ad-hoc settings. Although activating more transceivers on a module makes it easier to maintain LOS alignments between mobiles, it clearly uses more energy. In order to address explore tradeoff, this paper presents energy efficient mechanisms that aim to select an optimal subset of the directional transceivers in FSO modules.

The 19th IEEE Workshop on Local and Metropolitan Area Networks features invited papers in addition to regular track papers from both industry and academia. We received 32 submissions for regular papers. After a careful review process, the technical program committee (TPC) selected 10 regular papers and 4 short papers for presentation in the workshop program, resulting in 31% and 44% acceptance rates, respectively. Each regular submission received at least three reviews. We also received 8 invited paper submissions from experts performing research in areas related to the theme of this year's workshop: Seamless Services. We are very pleased to have the invited papers by Peng He, Thomas Mager, Paris Charalampou, Jean-Michel Dricot, Vanniarajan Chellappan, Dan Li, Gianluca Reali, Patrick Thiran and their co-authors. Each invited paper submission received at least two reviews.

Funding from the government agencies has been the driving force for the research and educational institutions particularly in the United States. The government funds billions of dollars every year to lead research initiatives that will shape the future. In this paper, we analyze the funds distributed by the National Science Foundation (NSF), a major source of research funding in the States, to understand the collaboration patterns among researchers and institutions. Using complex network analysis, we interpret the collaboration patterns at researcher, institution and state levels by constructing the corresponding networks based on the number of grants collaborated. We further analyze the directorates to identify the differences in collaboration trends between disciplines.

Many recently proposed clean slate Internet architectures essentially depend on more flexible and extended representation of Internet topology on which next generation routing protocols may operate. Representation of neighboring relationships between Internet Service Providers (ISPs) in finer granularity is promising to overcome many shortcomings of the current Internet architecture. Similarly, contract-switching paradigm promotes an ISP to define itself as a set of edge-to-edge (g2g) links that connect ingress and egress routers of its domain. Each link is represented by a contract which defines not only neighboring relationships with other domains but also economic (e.g., price), performance (e.g., quality of service parameters) and temporal (e.g., lifetime of the dedicated link) attributes attached to this g2g link. In this work, we introduce Path-Vector Contract Routing (PVCR) protocol which allows multi-metric, multi-hop negotiation of end-to-end inter-domain paths by leveraging path-vector style construction on top of g2g contract definitions. Our analysis on synthetic and real-world topologies show that Path-Vector Contract Routing has many promising properties such as rich route diversity, end-to-end multi-domain QoS and low control traffic. We also investigate inter-domain traffic engineering capabilities of PVCR which inherently considers economics of routing in its opportunistic settings.

We consider the contract-switching paradigm for studying the inter-domain traffic engineering problem. In the contract-switching paradigm, each ISP in the Internet is abstracted as a set of edge-to-edge contract links. We formulate the optimal routing problem for the contract-switching paradigm by considering three objectives, namely: 1) maximizing throughput, 2) minimizing delay, and 3) minimizing bandwidth usage. We solve the optimization problems on realistic network topologies and show that the routing solutions developed using the contract-switching paradigm provides significant improvement in performance compare to the BGP routing framework with respect to the three objectives. Moreover, our simulation study also reveals that the contract-switching paradigm performs close to the best performance that can be achieved in the Internet in the absence of any abstractions.

Overlay multicasting enabled many new overlay and peer-to-peer applications such as P2PTV, large-scale content sharing, and live video streaming. Sensitivity of these applications differs against various network performance metrics such as delay, loss, or bandwidth. We propose a generalized method of calculating overlay trees to increase user-perceived quality of performance-sensitive applications. We define and use the concept of virtual distance for constructing overlay trees. Abstracting applications' sensitivity to various performance metrics within the virtual distances, we aim to find the most appropriate parent for a peer according to the application's purpose. Calculating the virtual distance based on different criteria, but without protocol modification, makes the overlay multicast protocol satisfy different quality expectations. We show by simulation experiments that the protocol automatically calculates overlay trees based on delay or loss, depending on which is more important for the application under consideration.

Automated configuration and management of highly dynamic networks is a challenging problem for network practitioners. Such online optimization of systems can be performed in two ways: (i) using a separate model of the system for experimenting new configurations, (ii) using the system itself for experimentation without a separate system model. The former approach fails for dynamic networks with high failure rates or variable demand profile. In this paper, we take the latter approach and perform in- situ trials in a network to find better configurations of IGP link weights giving result to higher network throughput. Our approach follows a two-phase model where the online optimization process periodically goes into a "search" phase followed by network operation with the parameters found in the latest search phase. We use a black-box optimization algorithm, called Probabilistic Trans- Algorithmic Search (PTAS), to search for better IGP link weights and evaluate our approach in terms of key parameters such as search phase frequency and length.

Inter-domain routing has been long considered as an ongoing negotiation on end-to-end paths between service providers. Such negotiations were often believed to be effective in their form of bilateral and single-hop interactions between neighboring ISPs in a rather hierarchical market structure. Traffic engineering policies, multi-homing schemes and peering mechanisms have been often employed as only service performance improvement methods within this localized approach. However, several measurement studies on inter-domain routing have revealed that these methods are not effective at capturing diversity in performance levels and alternative paths offered by the Internet. Recently, several clean-slate Internet architecture proposals have introduced multi-hop negotiation mechanisms in an effort to revitalize inter-domain routing on the Internet. In this work, we quantify how effective these local policy exceptions can be in providing better quality paths. We also analyze the increasing benefits ripened by broadening wide-area route control capabilities of an ISP. Our analysis on traces captured from the Internet quantitatively shows that currently adopted local and single-hop policies are effective only to a certain extent, and multi-hop negotiation mechanisms can significantly increase the quality and performance of end-to-end paths.

It can be argued that, BGP, de-facto inter-domain routing protocol, provides fairly stable routes. Path stability is a desired product of that limited level of deterministic performance of BGP. To attain this performance level, BGP relies on keeping up-to-date (aggregated) global information by incurring the cost of control traffic and delayed convergence. In this work, we developed an Opportunistic Path-Vector (OPVR) protocol which provides nice trade-offs between path stability, routing scalability and path quality to enable flexible inter-domain level routing services. Our approach is to redefine routing problem as a set of smaller scale problems which can be solved locally without requiring a global coordination but local communication. We also provide guidelines on how to solve these localized routing problems efficiently. Our analysis show that our method provide a good compromise between scalability and opportunity through smartly randomized (non-deterministic) choices. Our experiments with OPVRs on Internet AS-level topology show us that OPVRs can provide non-deterministic, scalable path exploration mechanisms with reasonable control traffic cost.

Network management and automated configuration of large-scale networks is one of the crucial issues for Internet Service Providers (ISPs). Since wrong configurations might lead to an enormous amount of customer traffic to be lost, highly experienced network administrators are typically the ones who are trusted for the management and configuration of a running ISP network. We frame the management and experimentation of a network as a “game” for training network administrators without having to risk the network operation. The interactive environment treats the trainee network administrators as players of a game and tests them with various network failures or dynamics. To prototype the concept of “network management as a game”, we modified NS-2 to establish an interactive simulation engine and connected the modified engine to a graphical user interface for traffic animation and interactivity with the player. We present initial results from our game applied to a small set of players.

Wireless networking has conventionally been realized via radio frequency (RF) based communication technologies. However, the capacity of these networks are limited by the availability of the RF spectrum. Free-Space-Optical (FSO) communication has the potential to deliver wireless communication links at optical-level speeds. Although it has the advantage of high-speed modulation, maintenance of line-of-sight (LOS) between transceivers during an on-going transmission is an important issue since FSO transmitters are highly directional. In this paper, we present a prototype implementation of such multi-transceiver electronically-steered communication structures. Our prototype uses a simple LOS detection and establishment protocol and assigns logical data streams to appropriate physical links.We show that by using multiple directional transceivers we can maintain optical wireless links with minimal disruptions that are caused by relative mobility of communicating nodes.

The benefit of Class-of-Service (CoS) is an important topic in the "Network Neutrality" debate. Proponents of network neutrality suggest that over-provisioning is a viable alternative to CoS. We quantify the extra capacity requirement for an over-provisioned classless (i.e., best-effort) network compared to a CoS network providing the same delay or loss performance for premium traffic. We first develop a link model that quantifies this Required Extra Capacity (REC). For realistic traffic distributions (e.g., long-range dependent), we find the REC using ns-2 simulations of the CoS and classless links. Our primary contribution is in using these link models to quantify the REC for realistic network topologies under various scenarios including "closed loop" environments with traffic generated by TCP sources that adapt to the available capacity. We show that REC can be significant even when the proportion of premium traffic requiring performance assurances is small, a situation often considered benign for the over-provisioning alternative.

This paper presents packet-based simulation tools for free-space-optical (FSO) wireless communication. We implement the well-known propagation models for free-space-optical communication as a set of modules in NS-2. Our focus is on accurately simulating line-of-sight (LOS) requirement for two communicating antennas, the drop in the received power with respect to separation between antennas, and error behavior. In our simulation modules, we consider numerous factors affecting the performance of optical wireless communication such as visibility in the medium, divergence angles of transmitters, field of view of photo-detectors, and surface areas of transceiver devices.

Automated control and management of large-scale physical systems is a challenging problem in a wide variety of applications including: power grids, transportation networks, and telecommunication networks. Such systems require (i) data collection, (ii) secure data transfer to processing centers, (iii) data processing, and (iv) timely decision making and control actions. These tasks are complicated by the vast amount of data, the distributed sources of data, and the need for efficient data communication. In addition, large physical systems are often subdivided into separately owned subsystems. This multi-owner structure imposes physical, economic, market, and political constraints on the data transfer. These divisions make systems vulnerable to potential coordinated attacks. Defending against such attacks requires the infrastructures to be more automated and self-healing. Motivated by the challenge of a more efficient, secure and robust power grid, which is less vulnerable to blackouts due to cascaded events, this paper discusses some of the fundamental problems in designing future cyber-physical systems.

Wireless networking has conventionally been realized via radio-frequency-based communication technologies. Free-Space-Optical (FSO) communication with an innovative multi-element node design leverages spatially-diverse optical wireless links; making it a viable solution to the well-known diminishing per-node throughput problem in large-scale RF networks. Although it has the advantage of high-speed modulation, maintenance of line-of-sight between two FSO transceivers during a transmission is a crucial problem since FSO transmitters are highly directional. In this paper, we present our simulation efforts to make high-level assessments on throughput characteristics of FSO-MANETs while considering properties of FSO propagation and existence of multiple directional transceivers.

The enormous interest for peer-to-peer systems in recent years has prompted research into finding scalable and robust seeding and searching methods to support these overlay networks. Routing and search in these overlay networks have ranged from flooding-based unstructured techniques to structured ones mainly for popular and rate items respectively. In this paper, we propose a new method of establishing a virtual structure and introduce a technique to scalably route packets through an unstructured overlay network. We introduce virtual direction routing (VDR). VDR is a lightweight and scalable overlay network routing protocol that uses the concept of virtual directions to efficiently perform node information seeding and lookup. State information is replicated at nodes along virtual orthogonal lines originating from each node and periodically updated. When a path lookup is initiated, instead of flooding the network, query packets are also forwarded along virtual orthogonal lines until an intersection with the seeded state occurs. We show that VDR achieves high reachability with relatively low seed and search packet TTL even under high network churn. We also show that VDR scales well without imposing DHT-like graph structures (e.g., trees, rings, torus, coordinate-space) and the path stretch compared to random-walk protocols is very good. The tradeoff is added latency by choosing suboptimal paths.

Due to its high bandwidth spectrum, Free-Space-Optical (FSO) communication has the potential to bridge the capacity gap between backbone fiber links and mobile ad-hoc links, especially in the last-mile. Though FSO can solve the wireless capacity problem, it brings new challenges such as frequent disruption of wireless communication links (intermittent connectivity) and the line-of-sight (LOS) requirements. In this paper, we study a multi-transceiver spherical FSO structure as a basic building block for enabling optical spectrum in mobile ad-hoc networking. We outline optimal designs of such multi-transceiver subsystems such that coverage is maximized and crosstalk among neighboring transceivers is minimized. We propose a low-level packaging architecture capable of handling hundreds of transceivers on a single structure. We also present MANET transport performance over such multi-element mobile FSO structures in comparison to legacy RF-based MANETs.

In unstructured peer-to-peer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of a search on such unstructured P2P networks, as well as other networks. A key limitation of scale-free (power-law) topologies is the high load (i.e., high degree) on a very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store a large number of entries for construction of the overlay topology. Therefore, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scale-freeness of the overall topology, hence limited scale-free networks. Thus, it is expected that the efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate the construction of scale-free topologies with hard cutoffs (i.e., there are not any major hubs) and the effect of these hard cutoffs on the search efficiency. Interestingly, we observe that the efficiency of normalized flooding and random walk search algorithms increases as the hard cutoff decreases.

Despite the huge success of the Internet in providing basic communication services, the Internet architecture needs to be upgraded so as to provide end-to-end QoS services to its customers. Currently, a user or an enterprise that needs end-to-end bandwidth guarantees between two arbitrary points in the Internet for a short period of time has no way of expressing its needs. To allow these much needed basic QoS services, we propose a single-domain edge-to-edge (g2g) dynamic capacity contracting mechanism, where a network customer can enter into a bandwidth contract on a g2g path at a future time, at a predetermined price. For practical and economic viability, such forward contracts must involve a bailout option to account for bandwidth becoming unavailable at service delivery time, and must be priced appropriately to enable ISPs manage risks in their contracting and investments. Our design allows ISPs to advertise point-to-point different prices for each of their g2g paths instead of the current point-to-anywhere prices, allowing for better end-to-end paths, temporal flexibility and efficiency of bandwidth usage. We compute the risk-neutral prices for these g2g bailout forward contracts (BFCs), taking into account correlations between different contracts due to correlated demand patterns and overlapping paths. We implement this multiple g2g BFC framework on a realistic network model with Rocketfuel topologies, and evaluate our contract switching mechanism in terms of key network performance metrics like fraction of bailouts, revenue earned by the provider, and adaptability to link failures.

Broadcast TV distribution over an IP network requires stringent QoS constraints, such as low latency and loss. The main challenge to achieving these QoS objectives is how to design the network to respond to network failures. Streaming content in IPTV is typically delivered to the distribution points on the IP backbone using IP multicast, and in the case being considered, with protocol independent multicast source specific mode (PIM-SSM). A proven failure restoration technique at the IP layer is link-restoration using MPLS or layer-2 fast reroute (FRR). Link-based FRR creates a pseudo-wire or tunnel in parallel to the IP adjacencies (links) along the forwarding path used by the PIM tree. For each such tunnel both a primary and backup path are defined. The backup path is Layer-1-disjoint from the physical link and when the link fails, the pseudo-wire can be rapidly restored. Thus, single link failures are transparent to the interior gateway protocol (IGP). Although one may choose the back-up pathpsilas IGP link weights to avoid traffic overlap during any single link failure, multiple failures may still cause traffic overlap with FRR. We present a cross-layer restoration approach that combines both FRR-based restoration for single link failure and ldquohitlessrdquo (i.e., without loss) PIM tree reconfiguration algorithms to prevent traffic overlap when multiple failures occur.

The increased usage of directional methods of communications has prompted research into leveraging directionality in every layer of the network stack. In this paper, we explore the use of directionality in layer 3 to facilitate routing in highly mobile environments. We introduce mobile orthogonal rendezvous routing protocol (MORRP), a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding, node localization, and mobility. This relaxation is done by introducing a novel concept called the directional routing table (DRT) which maps a set-of-IDs to each directional interface to provide probabilistic routing information based on interface direction. We show that MORRP achieves connectivity with high probability even in highly mobile environments while maintaining only probabilistic information about destinations. We also compare MORRP with various proactive, reactive, and position-based routing protocols using single omni-directional interfaces and 8 directional interfaces and show that MORRP gains over 10-14X additional goodput vs. traditional protocols and 15-20% additional goodput vs. traditional protocols using multiple interfaces.

Provisioning of rich routing building blocks to mobile ad-hoc networking applications has been of high interest. Several MANET applications need flexibility in describing paths their traffic will follow. To accommodate this need, previous work has proposed several viable routing schemes such as Dynamic Source Routing (DSR) and Trajectory-Based Routing (TBR). However, tradeoffs involved in the interaction of these routing schemes and the application-specific requirements have not been explored. Especially, techniques to help the application to do the right routing choices are much needed. We consider techniques that minimize routing protocol state costs under application-based constraints. We study the constraint of ldquoaccuracyrdquo of the applicationpsilas desired route, as this constraint provides a range of choices to the applications. As a crucial part of this optimization framework, we investigate the tradeoff between the packet header size and the network state. We, then, apply our framework to the case of TBR with application-based accuracy constraints in obeying a given trajectory. We begin with simple discrete models to clarify the tradeoff between packet header size and network state. We show that the problem of accurate representation of a trajectory with the objective of minimizing the cost incurred due to header size and network state is difficult to solve optimally. Finally, we develop heuristics solving this problem and illustrate their performance.

Several protocol efficiency metrics (e.g., scalability, search success rate, routing reachability and stability) depend on the capability of preserving structure even over the churn caused by the ad hoc nodes joining or leaving the network. Preserving the structure becomes more prohibitive due to the distributed and potentially uncooperative nature of such networks, as in the peer-to-peer (P2P) networks. Thus, most practical solutions involve unstructured approaches while attempting to maintain the structure at various levels of protocol stack. The primary focus of this paper is to investigate construction and maintenance of scale-free topologies in a distributed manner without requiring global topology information at the time when nodes join or leave. We consider the uncooperative behavior of peers by limiting the number of neighbors to a pre-defined hard cutoff value (i.e., no peer is a major hub), and the ad hoc behavior of peers by rewiring the neighbors of nodes leaving the network. We also investigate the effect of these hard cutoffs and rewiring of ad-hoc nodes on the P2P search efficiency.

The benefit of Class-of-Service (CoS) is an important topic in the "Network Neutrality" debate. Proponents of network neutrality suggest that over-provisioning is a viable alternative to CoS. We quantify the extra capacity requirement for an over-provisioned classless (i.e., best-effort) network compared to a CoS network providing the same delay or loss performance for premium traffic. We first develop a link model that quantifies this Required Extra Capacity (REC). For bursty and realistic traffic distributions, we find the REC using ns-2 simulation comparisons of the CoS and classless link cases. We use these link models to quantify the REC for realistic network topologies. We show that REC can be significant even when the proportion of premium traffic is small, a situation often considered benign for the over-provisioning alternative.

The increased usage of directional methods of communications to improve medium reuse, network capacity, and bandwidth has prompted research into leveraging directionality in every layer of the network stack. Recently, there has been work on bringing the apparent capacity gains on layer 2 using directional communications methods to layer 3 by using directionality to route packets scalably in unstructured, flat networks. In their protocol, Orthogonal Rendezvous Routing Protocol, Cheng et al. [1] showed that by ”drawing” two lines orthogonal to each other at each node, it is possible to provide over 98% connectivity while maintaining only O(N3/2) evenly distributed states at a cost of only 1.2 path stretch. In this paper, we seek to provide more in-depth performance analysis by tuning additional factors such as the number of directions to transmit, the number of interfaces per node, among others, to understand its affect on varying network densities, topologies, connections, and traffic patterns. We show that by sending packets out in more directions, increased connectivity, smaller average path length, better goodput results only up to a point as compared to other routing protocols. The trade-off, however, is added state information maintained at each node and additional control packets received. We also show that the addition of more interfaces generally yields better packet delivery success, average path length, and goodput.

In unstructured peer-to-peer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of search on such unstructured P2P networks as well as other networks. A key limitation of scale- free (power-law) topologies is the high load (i.e. high degree) on very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store large number of entries for construction of the overlay topology. So, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scale-freeness of the overall topology. Thus, it is expected that efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate construction of scale-free topologies with hard cutoffs and effect of these hard cutoffs on the search efficiency.

The desire or ability of an ISP to provide differentiated service is a current hotly debated topic. In this paper, we quantify the value of having differentiated service (i.e., class-of-service (CoS)) support in an IP backbone. We compare the capacity requirements of a Diffserv environment providing service for applications that require delay or loss assurances in comparison to a network that provides classless (i.e., best-effort) service and still has to meet the same performance assurances. Our modeling framework first develops a link model that quantifies the required extra capacity (REC) in order for a classless link to provide the same level of performance as experienced by premium class traffic passing through a fixed capacity CoS link. We develop the REC calculations for the cases when average delay or the average loss probability is the target performance goal with Poisson or Markov modulated Poisson process (MMPP) input traffic. Our primary contribution is in quantifying the value of the CoS support in a network setting.

Free-Space Optical communication technology is a potential solution to the last mile or broadband access problem. Conventional free-space optical (FSO) communication is over a single link between two nodes. We explore multi-channel FSO communication system using compact (a maximum of a Sq.Ft) 2-dimensional antennas with multiple communication links between them to achieve very high aggregate bandwidths (100's of Gbps). But, close packaging of optical channels on the arrays causes inter-channel interference, reducing per channel capacity. We model the error due to inter-channel interference for such arrays and estimate the channel capacity. We address the multi-channel interference issue by both array design and by employing optical orthogonal codes (OOCs) for free-space optical communications and show that we can achieve multi Gbps bandwidths using such arrays. Possible applications for such multi-channel FSO systems can be in multi-hop broadband access networks or mesh networks and in back haul, connecting wireless base stations.

Routing in multi-hop wireless networks involves the indirection from a persistent name (or ID) to a locator. One of the biggest issues in routing is providing adequate connectivity while scaling the network. Recently, Bow-Nan Cheng et al., (2006) has attempted to mitigate this issue by using directional communication methods to find intersections between source-rendezvous and rendezvous-destination paths, providing effective routing in unstructured, flat networks. Cheng et al. showed that by "drawing" two lines orthogonal to each other at each node, it is possible to provide over 98% connectivity while maintaining only order O(N3/2) states. It is interesting, however to investigate what happens when additional lines are "drawn" and how that affects connectivity, path length and state complexity. In this paper, we examine how transmitting along one, two, three, and four lines affects routing and provide both analytical bounds for connectivity as well as packetized simulations on how these methods stack up in a more realistic environment. We show that by sending packets out in more directions, increased connectivity and smaller average path length results only up to a point. The trade-off, however, is added state information maintained at each node. We also show that in mobile environments, adding additional lines increases the chances for successful packet delivery only marginally.

Routing in multi-hop wireless networks involves the indirection from a persistent name (or ID) to a locator. Concepts such as coordinate space embedding help reduce the number and dynamism complexity of bindings and state needed for this indirection. Routing protocols which do not use such concepts often tend to flood packets during route discovery or dissemination, and hence have limited scalability. In this paper, we introduce orthogonal rendezvous routing protocol (ORRP) for meshed wireless networks. ORRP is a lightweight, but scalable routing protocol utilizing directional communications (such as directional antennas or free-space-optical transceivers) to relax information requirements such as coordinate space embedding and node localization. The ORRP source and ORRP destination send route discovery and route dissemination packets respectively in locally-chosen orthogonal directions. Connectivity happens when these paths intersect (i.e. rendezvous). We show that ORRP achieves connectivity with high probability even in sparse networks with voids. ORRP scales well without imposing DHT-like graph structures (eg: trees, rings, torus etc). The total state information required is O(N3/2) for N-node networks, and the state is uniformly distributed. ORRP does not resort to flooding either in route discovery or dissemination. The price paid by ORRP is suboptimality in terms of path stretch compared to the shortest path; however we characterize the average penalty and find that it is not severe.

This paper considers the tradeoffs between packet header size, network state and accuracy of representation in wireless networks which use trajectory based routing techniques. The models presented here are applicable in sensor networks for which trajectory based routing techniques have previously been proposed. We begin with simple discrete models to make clear the tradeoff between header size and network state. We show that the problem of accurate representation of a trajectory with the objective of minimizing the cost incurred due to header size and network state is difficult to solve optimally. Therefore, we present two heuristics to solve this problem. We note that this work leads to further interesting problems when applied to practical systems

In this paper we analyze the error performance of free-space optical (FSO) communication over multiple hops. We first develop an error model for a single hop based on visibility, atmospheric attenuation, and geometric spread of the light beam. We model atmospheric visibility by Gaussian distributions with mean and variance values to reflect clear and adverse weather conditions. Based on this, we find the end-to-end bit error distribution of the FSO link for single hop and multi-hop scenarios. We present simulation results for decoded relaying, where each hop decodes the signal before retransmitting. We demonstrate that multi-hop FSO communication achieves a significant reduction in the mean bit error rate and also reduces the variance of the bit error rate. We argue that by lowering mean error and error variance, multi-hop operation facilitates an efficient system design and improves the reliability of the FSO link by application of specific coding schemes (such as forward error correction techniques).

An automated method is presented for selecting optimal parameter settings for vessel/neurite segmentation algorithms using the minimum description length principle and a recursive random search algorithm. It trades off a probabilistic measure of image-content coverage against its conciseness. It enables nonexpert users to select parameter settings objectively, without knowledge of underlying algorithms, broadening the applicability of the segmentation algorithm, and delivering higher morphometric accuracy. It enables adaptation of parameters across batches of images. It simplifies the user interface to just one optional parameter and reduces the cost of technical support. Finally, the method is modular, extensible, and amenable to parallel computation. The method is applied to 223 images of human retinas and cultured neurons, from four different sources, using a single segmentation algorithm with eight parameters. Improvements in segmentation quality compared to default settings using 1000 iterations ranged from 4.7%-21%. Paired t-tests showed that improvements are statistically significant (p < 0.0005). Most of the improvement occurred in the first 44 iterations. Improvements in description lengths and agreement with the ground truth were strongly correlated (p = 0.78).

Routing in ad-hoc networks is a complicated task because of many reasons. The nodes are low-memory, low-powered, and they cannot maintain routing tables large enough for well-known routing protocols. Because of that, greedy forwarding at intermediate nodes is desirable in ad-hoc networks. Also, for traffic engineering, multi-path capabilities are important. So, it is desirable to define routes at the source like in source based routing (SBR) while performing greedy forwarding at intermediate nodes. In this paper, we investigate trajectory-based routing (TBR) which was proposed as a middle-ground between SBR and greedy forwarding techniques. We address various issues regarding implementation of TBR. We also provide techniques to efficiently forward packets along a trajectory defined as a parametric curve.

One of the biggest obstacles for implementing congestion pricing is the pricing-time scale. The Internet traffic is highly variant and hard to control without a mechanism that operates on very low time-scales, i.e. on the order of round-trip-times (RTTs). However, pricing naturally operates on very large time-scales because of human involvement. So, in order to put tight control on congestion through pricing, new implementation methods and architectures are needed for congestion pricing. In order to solve this problem, we propose a novel approach pricing over congestion control (POCC). The essence of POCC is to overlay congestion pricing on top of an underlying congestion control scheme which enforces a much tighter control than pricing. This way congestion in the interior network is controlled very tightly, while pricing is done at time-scales large enough to incorporate human involvement.

Since optimization of networks pricing has attracted significant attention over the last decade. These studies assumed concave utility functions for users and derived optimal pricing strategies for the network provider. In this paper, we consider effect of user's elasticity to price and bandwidth on optimality of pricing. We first derive optimal pricing strategy for the case logarithmic user utilities. Then, we investigate two types of elasticity for users: demand-price elasticity and utility-bandwidth elasticity. By incorporating these two elasticities, we develop a non-logarithmic utility function for users. Finally, we derive an optimal pricing strategy for the non-logarithmic user utilities and illustrate that pricing strategy should be more conservative when the elasticities increase.

One of the key issues for implementing congestion pricing is the pricing granularity (i.e. pricing interval or time scale). The Internet traffic is highly variant and hard to control without a mechanism that operates on very low time-scales, i.e. on the order of round-trip-times (RTTs). However, pricing naturally operates on very large times-scales because of human involvement. Moreover, structure of wide-area networks does not allow frequent price updates for many reasons, such as RTTs are very large for some cases. In this paper, we investigate the issue of pricing granularity, identify problems, and propose solutions.

We present a baseline implementation strategy for the well-known Smart Market pricing scheme on DiffServ. Our strategy models Smart Market's theoretically defined properties as much as possible. In order to suit the DiffServ framework, we propose ways of focusing Smart Market's complex operations at the edges while keeping the interior simple. Based on the proposed implementation strategy, we develop a packet-based simulation of Smart Market. By simulation, we then investigate Smart Market's performance in terms of stability, fairness, and service differentiation on UDP and TCP traffic. We also look at the importance of packet sorting (i.e. sorting of packets at routers according to their bids as proposed in Smart Market) in Smart Market's performance. By several simulations, we find that packet sorting does not really improve the performance for all three metrics (stability, fairness, and service differentiation). So, it is not necessary to implement packet sorting for Smart Market's possible deployment, thus significantly reducing the necessity for router upgrades.

This paper describes a new class of deadlock-free routing algorithms for irregular networks based on ordered links. In this case, the links are ordered by partitioning them into a set of layers, each layer containing a spanning tree (when possible). Deadlock free routes can then be derived by using links with non-decreasing order. The deadlock-freedom property is proved. Two different implementations of the routing algorithm are studied. The resultant performance of these algorithms is then compared to other known algorithms: the shortest-path algorithm (which may result in deadlocks) and the up*/down* algorithm. Various performance metrics are considered, including path-length, network capacity, fault tolerance and time of computation. We argue that network capacity is the most important metric to optimize. It is shown that the proposed algorithms are promising since they usually achieve higher network capacity than up*/down*, while they perform only slightly worse than up*/down* in other metrics.