Showing papers on "Testbed published in 2007"

Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks

Abstract: To increase the utilization of the available frequency channel space in 802.11-based wireless mesh networks, recent work has explored solutions based on multi-radio stations. This paper reports on our design and experimental study of a distributed, self-stabilizing mechanism that assigns channels to multi-radio nodes in wireless mesh networks. We take a modular approach by decoupling the channel selection decision from the data forwarding mechanism, which makes our solution readily applicable to real-world operation when used with emerging multi-radio routing solutions. We demonstrate the efficacy of our protocol on a real-world, 14-node testbed comprised of nodes, each equipped with an 802.11a card and an 802.11g card. We show via extensive measurements on our testbed that our channel assignment algorithm improves the network capacity by 50% in comparison to a homogeneous channel assignment and by 20% in comparison to a random assignment.

First Experience with CarTorrent in a Real Vehicular Ad Hoc Network Testbed

Abstract: Content sharing using cooperative peer-to-peer model has become increasingly more popular in a vehicular ad hoc network (VANET). The small transmission window from a vehicle to an access point (AP), high mobility of vehicles, and intermittent and short-lived connectivity to an AP provide incentives for vehicles to cooperate with one another to obtain information from the Internet. These characteristics of VANETs naturally stipulate the use of cooperative peer-to-peer paradigm and motivate related content sharing application such as CarTorrent. Building upon previous research on SPAWN [6, 1], we have implemented CarTorrent and deployed it on a real VANET. We have run extensive field tests to affirm the feasibility of the peer-to-peer file sharing application tailored to VANET. To the best of our knowledge, the deployment of such a content sharing application on a real vehicular ad hoc testbed is the first of its kind.

Managing Power Consumption and Performance of Computing Systems Using Reinforcement Learning

Abstract: Electrical power management in large-scale IT systems such as commercial data-centers is an application area of rapidly growing interest from both an economic and ecological perspective, with billions of dollars and millions of metric tons of CO2 emissions at stake annually. Businesses want to save power without sacrificing performance. This paper presents a reinforcement learning approach to simultaneous online management of both performance and power consumption. We apply RL in a realistic laboratory testbed using a Blade cluster and dynamically varying HTTP workload running on a commercial web applications middleware platform. We embed a CPU frequency controller in the Blade servers' firmware, and we train policies for this controller using a multi-criteria reward signal depending on both application performance and CPU power consumption. Our testbed scenario posed a number of challenges to successful use of RL, including multiple disparate reward functions, limited decision sampling rates, and pathologies arising when using multiple sensor readings as state variables. We describe innovative practical solutions to these challenges, and demonstrate clear performance improvements over both hand-designed policies as well as obvious "cookbook" RL implementations.

Balancing traffic load in wireless networks with curveball routing

Abstract: We address the problem of balancing the traffic load in multi-hop wireless networks. We consider a point-to-point communicating network with a uniform distribution of source-sink pairs. When routing along shortest paths, the nodes that are centrally located forward a disproportionate amount of traffic. This translates into increased congestion and energy consumption. However, the maximum load can be decreased if the packets follow curved paths. We show that the optimum such routing scheme can be expressed in terms of geometric optics and computed by linear programming. We then propose a practical solution, which we call Curveball Routing which achieves results not much worse than the optimum.We evaluate our solution at three levels of fidelity: a Java high-level simulator, the ns2 simulator, and the Intel Mirage Sensor Network Testbed. Simulation results using the high-level simulator show that our solution successfully avoids the crowded center of the network, and reduces the maximum load by up to 40%. At the same time, the increase of the expected path length is minimal, i.e., only 8% on average. Simulation results using the ns2 simulator show that our solution can increase throughput on moderately loaded networks by up to 15%, while testbed results show a reduction in peak energy usage by up to 25%. Our prototype suggests that our solution is easily deployable.

WARP, a Unified Wireless Network Testbed for Education and Research

Abstract: In this paper, we introduce the wireless open-access research platform (WARP) developed at CMC lab, Rice University. WARP provides a scalable and configurable platform mainly designed to prototype wireless communication algorithms for educational and research oriented applications. Its programmability and flexibility makes it easy to implement various physical and network layer protocols and standards. Moreover, the online open-access WARP repository is used to document and share different wireless architectures and cross-layer designs developed at educational and research centers. This repository is a fast and easy solution for students and researchers with a wide range of backgrounds in hardware implementation and algorithm development to collaborate and initiate multi-disciplinary system designs.

Web search from a bus

Abstract: Opportunistic connections to the Internet from open wireless access points is now commonly possible in urban areas. Vehicular networks can opportunistically connect to the Internet for several seconds via open access points. In this paper, we adapt the interactive process of web search and retrieval to vehicular networks with intermittent Internet access. Our system, called Thedu, has mobile nodes use an Internet proxy to collect search engine results and prefetch result pages. The mobile nodes download the pre-fetched web pages from the proxy. Our contribution is a novel set of techniques to make aggressive but selective prefetching practical, resulting in a significantly greater number of relevant web results returned to mobile users. In particular, we prioritize responses in the order of the usefulness of the response to the query, that allows the mobile node to download the most useful response first. To evaluate our scheme, we deployed Thedu on DieselNet, our vehicular testbed operating in a micro-urban area around Amherst, MA. Using a simulated workload, we find that users can expect four times as many useful responses to web search queries compared to not using Thedu's mechanisms. Moreover, the mean latency in receiving the first relevant response for a query is 2.7 minutes for our deployment; we expect Thedu to have even better performance in larger cities that have densely populated open APs.

CitySense: A Vision for an Urban-Scale Wireless Networking Testbed

Abstract: In this paper, we present the vision for an open, urban-scale wireless networking testbed, called CitySense, with the goal of supporting the development and evaluation of novel wireless systems that span an entire city. CitySense is currently under development and will consist of about 100 Linux-based embedded PCs outfitted with dual 802.11a/b/g radios and various sensors, mounted on buildings and streetlights across the city of Cambridge. CitySense takes its cue from citywide urban mesh networking projects, but will differ substantially in that nodes will be directly programmable by end users. The goal of CitySense is explicitly not to provide public Internet access, but rather to serve as a new kind of experimental apparatus for urban-scale distributed systems and networking research efforts. In this paper we motivate the need for CitySense and its potential to support a host of new research and application developments. We also outline the various engineering challenges of deploying such a testbed as well as the research challenges that we face when building and supporting such a system.

A comparative evaluation of search techniques for query-by-humming using the MUSART testbed

Abstract: Query-by-humming systems offer content-based searching for melodies and require no special musical training or knowledge. Many such systems have been built, but there has not been much useful evaluation and comparison in the literature due to the lack of shared databases and queries. The MUSART project testbed allows various search algorithms to be compared using a shared framework that automatically runs experiments and summarizes results. Using this testbed, the authors compared algorithms based on string alignment, melodic contour matching, a hidden Markov model, n-grams, and CubyHum. Retrieval performance is very sensitive to distance functions and the representation of pitch and rhythm, which raises questions about some previously published conclusions. Some algorithms are particularly sensitive to the quality of queries. Our queries, which are taken from human subjects in a realistic setting, are quite difficult, especially for n-gram models. Finally, simulations on query-by-humming performance as a function of database size indicate that retrieval performance falls only slowly as the database size increases. © 2007 Wiley Periodicals, Inc.

Advanced Diagnostics and Prognostics Testbed

Abstract: Researchers in the diagnosis community have developed a number of promising techniques for system health management. However, realistic empirical evaluation and comparison of these approaches is often hampered by a lack of standard data sets and suitable testbeds. In this paper we describe the Advanced Diagnostics and Prognostics Testbed (ADAPT) at NASA Ames Research Center. The purpose of the testbed is to measure, evaluate, and mature diagnostic and prognostic health management technologies. This paper describes the testbed’s hardware, software architecture, and concept of operations. A simulation testbed that accompanies ADAPT, and some of the diagnostic and decision support approaches being investigated are also discussed.

Traffic-Aware Channel Assignment in Enterprise Wireless LANs

Abstract: Campus and enterprise wireless networks are increasingly characterized by ubiquitous coverage and rising traffic demands. Efficiently assigning channels to access points (APs) in these networks can significantly affect the performance and capacity of the WLANs. The state-of-the-art approaches assign channels statically, without considering prevailing traffic demands. In this paper, we show that the quality of a channel assignment can be improved significantly by incorporating observed traffic demands at APs and clients into the assignment process. We refer to this as traffic-aware channel assignment. We conduct extensive trace-driven and synthetic simulations and identify deployment scenarios where traffic-awareness is likely to be of great help, and scenarios where the benefit is minimal. We address key practical issues in using traffic-awareness, including measuring an interference graph, handling non-binary interference, collecting traffic demands, and predicting future demands based on historical information. We present an implementation of our assignment scheme for a 25-node WLAN testbed. Our testbed experiments show that traffic-aware assignment offers superior network performance under a wide range of real network configurations. On the whole, our approach is simple yet effective. It can be incorporated into existing WLANs with little modification to existing wireless nodes and infrastructure.

Enhancing Energy Efficiency in Multi-tier Web Server Clusters via Prioritization

Abstract: This paper investigates the design issues and energy savings benefits of service prioritization in multi-tier Web server clusters In many services, classes of clients can be naturally assigned different priorities based on their performance requirements We show that if the whole multi-tier system is effectively prioritized, additional power and energy savings are realizable while keeping an existing cluster-wide energy management technique, through exploiting the different performance requirements of separate service classes We find a simple prioritization scheme to be highly effective without requiring intrusive modifications to the system In order to quantify its benefits, we perform extensive experimental evaluation on a real testbed It is shown that the scheme significantly improves both total system power savings and energy efficiency, at the same time as improving throughput and enabling the system to meet per-class performance requirements

BlueTorrent: Cooperative Content Sharing for Bluetooth Users

Abstract: People wish to enjoy their everyday lives in various ways, among which entertainment plays a major role. In order to improve lifestyle with more ready access to entertainment content, we propose BlueTorrent, a P2P file sharing application based on ubiquitous Blue tooth-enabled devices such as PDAs, cellphones and smart phones. Using BlueTorrent, people can share audio/video contents as they move about shopping malls, airports, subway stations etc. BlueTorrent poses new challenges caused by limited bandwidth, short communications range, mobile users and variable population density. A key ingredient is efficient peer discovery. This paper approaches the problem by analyzing the Bluetooth periodic inquiry mode and by finding the optimum inquiry/connection time settings. At the application layer, the BlueTorrent index/block dissemination protocol is then designed and analyzed. The entire system is integrated and implemented both in simulation and in an experimental testbed. Simulation and measurement results are used to evaluate and validate the performance of BlueTorrent in content sharing scenarios

MDG: measurement-driven guidelines for 802.11 WLAN design

Abstract: Dense deployments of WLANs suffer from increased interference and as a result, reduced capacity. There are three main functions used to improve the overall network capacity: a) intelligent frequency allocation across APs, b) load-balancing of user affiliations across APs, and c) adaptive power-control for each AP. Several algorithms have been proposed in each category, but so far, their evaluation has been limited to: (a) each approach in isolation and, (b)simulations or small-scale testbeds. In this paper, we ask the question: what is the best way to combine these different functions? Our focus is to fully explore the interdependencies between the three functions in order to understand when and how to deploy them on a network. We follow a measurement-driven study to quantify the effects of three previously proposed optimization schemes (one for each category) on a relatively large testbed and in many different scenarios. Surprisingly, we find that blindly applying all the three optimization schemes is not always preferable; it can sometimes degrade the performance by as much as 24% compared to using only two of the schemes. We discover that there are explicit conditions that are conducive for applying specific combinations of the optimization schemes. We capture those conditions within a comprehensive framework, which we call MDG (Measurement-Driven Guidelines). While we derive suchguidelines based on measurements on one experimental testbed, we test their applicability and efficacy on a second testbed in a different location. We show that our framework improves network capacity consistently acrossboth testbeds, with improvements ranging from 22% to 142% with 802.11a, and 103% to 274% with 802.11g.

Early Results on Hydra: A Flexible MAC/PHY Multihop Testbed

Abstract: Hydra is a flexible wireless network testbed being developed at UT Austin. Our focus is networks that support multiple wireless hops and where the network, especially the MAC, takes advantage of sophisticated PHY techniques, such as OFDM and MIMO. We argue that for this domain simulation alone is not adequate and that working prototypes are needed to validate algorithms and protocols. Hydra nodes consist of a flexible RF front-end and a general purpose machine with a software based MAC and PHY. Using the frameworks of the Click modular router and GNU radio and coding in C++ makes it relatively easy to implement working prototypes of cross-layer designs that require custom MACs and PHYs. We present the architecture and implementation of Hydra, as well as a preliminary cross-layer design experiment for a rate-adaptive MAC. These early results show Hydra is a capable prototyping tool for wireless network research.

EnviroMic: Towards Cooperative Storage and Retrieval in Audio Sensor Networks

Abstract: This paper presents EnviroMic, a novel distributed acoustic monitoring, storage, and trace retrieval system. Audio represents one of the least exploited modalities in sensor networks to date. The relatively high frequency and large size of audio traces motivate distributed algorithms for coordinating recording tasks, reducing redundancy of data stored by nearby sensors, filtering out silence, and balancing storage utilization in the network. Applications of acoustic monitoring with EnviroMic range from the study of mating rituals and social behavior of animals in the wild to audio surveillance of military targets. EnviroMic is designed for disconnected operation, where the luxury of having a basestation cannot be assumed. We implement the system on a Tiny OS-based platform and systematically evaluate its performance through both indoor testbed experiments and a preliminary outdoor deployment. Results demonstrate up to a 4-fold improvement in effective storage capacity of the network compared to uncoordinated recording.

A control theory approach to throughput optimization in multi-channel collection sensor networks

Abstract: Most currently deployed sensor networks use the same channel to communicate information among nodes. This is a source of great inefficiency as it poorly utilizes the available wireless spectrum. This paper takes advantage of radio capabilities of MicaZ motes that can communicate on multiple frequencies as specified in the 802.15.4 standard. We consider the case of a data collection sensor network where multiple base-stations are responsible for draining data from sensor nodes. A key question becomes how to assign nodes to wireless channels such that network throughput is maximized. The problem is reduced to one of load balancing. A control theoretical approach is used to design a self-regulating load-balancing algorithm that maximizes total network throughput. It is evaluated both in simulation and on an experimental testbed. The results demonstrate a significant performance improvement. It is shown that a control theory approach is indeed needed to guarantee stability in data collection networks and prevent undue oscillation of nodes among different wireless channels upon dynamic changes in load conditions.

Design, deployment, and use of the DETER testbed

Abstract: The DETER testbed provides infrastructure for conducting medium-scale repeatable experiments in computer security, especially experiments that involve malicious code. Built using Utah's EMULAB, the DETER testbed has been configured and extended to provide stronger assurances for isolation and containment. This paper provides information on the capabilities of the DETER testbed and discusses the lessons learned from its deployment. Our strategies for containment are described and future plans discussed.

The MIT Indoor Multi-Vehicle Flight Testbed

Abstract: This paper and video present the components and flight tests of an indoor, multi-vehicle testbed that was developed to study long duration UAV missions in a controlled environment. This testbed is designed to use real hardware to examine research questions related to single- and multi-vehicle health management, such as vehicle failures, refueling, and maintenance. The testbed has both aerial and ground vehicles that operate autonomously in a large, indoor flight test area and can be used to execute many different mission scenarios. The success of this testbed is largely related to our choice of vehicles, sensors, and the system's command and control architecture. The video presents flight test results from single- and multi-vehicle experiments over the past year.

On the accuracy of omnet++ in the wireless sensornetworks domain: simulation vs. testbed

Abstract: In this paper we present a first effort in assessing the reliability of OMNeT++ and the MAC Simulator framework insimulating Wireless Sensor Networks. A collection of metricson the flooding algorithm running on a simple testbed made of few Tmote Sky is used as reference to evaluate the qualityof the simulation results. Our experiments show that simulation results tend to over-estimate the metrics collected inthe testbed. A correcting factor derived from experimental evidences must be considered in order to improve the simulation results. At the best of our knowledge, this is thefirst result about the accuracy of OMNet++ in the wireless sensor network domain.

Analytic, Simulation, and Empirical Evaluation of Delay/Fault-Tolerant Mobile Sensor Networks

Abstract: The delay/fault-tolerant mobile sensor network (DFT-MSN) has been proposed for pervasive information gathering. DFT-MSN distinguishes itself from conventional sensor networks by several unique characteristics such as sensor mobility, loose connectivity, and delay/fault tolerability. This paper focuses on the performance evaluation of DFT-MSN. We first introduce a queuing model by using Jackson network theory. While the queuing model is based on a few simplification assumptions for analytic tractability, it provides insights into the queuing behavior of the mobile sensors in DFT-MSN. Extensive simulations are performed under realistic environment and assumptions. Our simulation results show that the dynamic DFT-MSN data delivery scheme achieves the highest message delivery ratio with acceptable delay and transmission overhead, compared with simple schemes such as flooding and direct transmission or other approaches in the literature such as Zebranet. We have also implemented a DFT-MSN testbed by deploying crossbow motes for noise level monitoring in our university library. Though in a small scale, the testbed demonstrates the feasibility of DFT-MSN and provides guidance for future large scale deployment.

End-to-End Routing for Dual-Radio Sensor Networks

Abstract: Dual-radio, dual-processor nodes are an emerging class of wireless sensor network devices that provide both low-energy operation as well as substantially increased computational performance and communication bandwidth for applications. In such systems, the secondary radio and processor operates with sufficiently low power that it may remain always vigilant, while the main processor and primary, high-bandwidth radio remain off until triggered by the application. By exploiting the high energy efficiency of the main processor and primary radio along with proper usage, net operating energy benefits are enabled for applications. The secondary radio provides a constantly available multi-hop network, while paths in the primary network exist only when required. This paper describes a topology control mechanism for establishing an end-to-end path in a network of dual-radio nodes using the secondary radios as a control channel to selectively wake up nodes along the required end-to-end path. Using numerical models as well as testbed experimentation, we show that our proposed mechanism provides significant energy savings of more than 60% compared to alternative approaches, and that it incurs only moderately greater application latency.

Performance Measurements of CSMA/CA-Based Wireless Sensor Networks for Industrial Applications

Abstract: The performance of modern wireless communication systems are strictly related to the adopted medium access mechanism. An effective one, based on the carrier sense multiple access with collision avoidance technique, is hereinafter investigated. In particular, the performance of a CSMA/CA-based wireless sensor network, designed for industrial monitoring and performing both cyclic polling and acyclic alarm management, are analyzed. Effects of in-channel interference are also studied. The aim of the paper is to gain, from practical experiments, results and guidelines useful for the measurement and optimization of CSMA/CA-based sensor network performance, when employed for industrial monitoring. In such direction, a suitable IEEE 802.15.4 wireless sensors' testbed has been deployed and an high layer protocol for industrial monitoring has been implemented. The results obtained from the experiments carried out are shown.

End-to-end Routing for Dual-Radio Sensor Networks

Abstract: Dual-radio, dual-processor nodes are an emerging class of Wireless Sensor Network devices that provide both low- energy operation as well as substantially increased computational performance and communication bandwidth for applications. In such systems, the secondary radio and processor operates with sufficiently low power that it may remain always vigilant, while the the main processor and primary, high-bandwidth radio remain off until triggered by the application. By exploiting the high energy efficiency of the main processor and primary radio along with proper usage, net operating energy benefits are enabled for applications. The secondary radio provides a constantly available multi-hop network, while paths in the primary network exist only when required. This paper describes a topology control mechanism for establishing an end-to-end path in a network of dual-radio nodes using the secondary radios as a control channel to selectively wake up nodes along the required end-to-end path. Using numerical models as well as testbed experimentation, we show that our proposed mechanism provides significant energy savings of more than 60% compared to alternative approaches, and that it incurs only moderately greater application latency.

4VP: A Novel Meta OS Approach for Streaming Programs in Ubiquitous Computing

Abstract: With the rapid improvements in hardware, software and networks, the computing paradigm has also shifted from mainframe computing to ubiquitous or pervasive computing, in which users can focus on their desired services rather than specific computing devices and technologies. However, the emerging of ubiquitous computing has brought many challenges, one of which is that it is hard to allow users to freely obtain desired services, such as heterogeneous OSes and applications via different light-weight devices. We have proposed a new paradigm, called Transparent Computing, to store and manage the commodity programs including OS codes centrally, while stream them to be run in non-state clients. This leads to a service-centric computing environment, in which users can select the desired services on demand, without concerning these services' administrations, such as their installation, maintenance, management, upgrade, and so on. In this paper, we introduce a novel concept: Meta OS to support such program streaming through a distributed 4VP+ platform. Based on this platform, a pilot system has been implemented and it supports Windows and Linux environments. We verify the effectiveness of the platform through both real deployments and testbed experiments. The evaluation results suggest that 4VP+ platform is a feasible and promising solution for future computing infrastructure in ubiquitous computing.

Log summarization and anomaly detection for troubleshooting distributed systems

Abstract: Today's system monitoring tools are capable of detecting system failures such as host failures, OS errors, and network partitions in near-real time. Unfortunately, the same cannot yet be said of the end-to-end distributed software stack. Any given action, for example, reliably transferring a directory of files, can involve a wide range of complex and interrelated actions across multiple pieces of software: checking user certificates and permissions, getting details for all files, performing third-party transfers, understanding re-try policy decisions, etc. We present an infrastructure for troubleshooting complex middleware, a general purpose technique for configurable log summarization, and an anomaly detection technique that works in near-real time on running Grid middleware. We present results gathered using this infrastructure from instrumented Grid middleware and applications running on the Emulab testbed. From these results, we analyze the effectiveness of several algorithms at accurately detecting a variety of performance anomalies.

Using Open Web Services for urban data management: A testbed resulting from an OGC initiative for offering standard CAD/GIS/BIM services

Abstract: In 2006, the Open Geospatial Consortium (OGC) started an initiative for gathering requirements and defining OGC Web Services that integrate information resources and workflows from the world of Architecture Engineering and Construction (AEC) with the world of Open Geospatial Web Services. While the Geospatial world has typically concerned itself with information about the out-of doors, and largely two or two-and-a-half dimensional information as would be found in maps, images and terrain models, there are many assets and activities that occur in the three dimensional context of buildings. Integration of the information resources of the AEC world with Open Geospatial Web Services will provide very important information resources for decision makers in urban environments, in situations like disaster management.

SoftMAC: Layer 2.5 Collaborative MAC for Multimedia Support in Multihop Wireless Networks

Abstract: In this paper, we present the challenges in supporting multimedia, in particular, VoIP services over multihop wireless networks using commercial IEEE 802.11 MAC DCF hardware, and propose a novel software solution, called Layer 2.5 SoftMAC. Our proposed SoftMAC resides between the IEEE 802.11 MAC layer and the IP layer to coordinate the real-time (RT) multimedia and best-effort (BE) data packet transmission among neighboring nodes in a multihop wireless network. To effectively ensure acceptable VoIP services, channel busy time and collision rate need to be well controlled below appropriate levels. Targeted at this, our SoftMAC architecture employs three key mechanisms: 1) distributed admission control for regulating the load of RT traffic, 2) rate control for minimizing the impact of BT traffic on RT one, and 3) nonpreemptive priority queuing for providing high priority service to VoIP traffic. To evaluate the efficacy of these mechanisms, extensive simulations are conducted using the network simulator NS2. We also implement our proposed SoftMAC as a Windows network driver interlace specification (NDIS) driver and build a multihop wireless network testbed with 32 wireless nodes equipped with IEEE 802.11 a/b/g combo cards. Our evaluation and testing results demonstrate the effectiveness of our proposed software solution. Our proposed collaborative SoftMAC framework can also provide good support for A/V streaming in home networks where the network consists of hybrid WLAN (wireless LAN) and Ethernet

Creating a European SCADA Security Testbed

Abstract: Supervisory control and data acquisition (SCADA) systems are commonly used to monitor and control critical infrastructure assets. However, over the past two decades, they have evolved from closed, proprietary systems to open networks comprising commodity platforms running common operating systems and TCP/IP stacks. The open architecture and increased connectivity provide more functionality and reduce costs, but they significantly increase the vulnerabilities and the exposure to threats. Since SCADA systems and the critical infrastructureassets they control must have 24-7 availability, it is imperative to understand and manage the risk. This paper makes the case for a European SCADA security testbed that can be used to analyze vulnerabilities threats and the impact of attacks, ultimately helping design new architectures and robust security solutions. The paper also discusses testbed requirements, deployment strategies and potential hurdles.

A 320-Gb/s Capacity (32-User $\times$ 10 Gb/s) SPECTS O-CDMA Network Testbed With Enhanced Spectral Efficiency Through Forward Error Correction

Abstract: This paper demonstrates a high-performance optical-code-division-multiple-access (O-CDMA) network testbed using the spectral phase encoded time spreading (SPECTS) method. Through additional time and polarization multiplexing, a total of 32 10-Gb/s users are supported while sharing eight O-CDMA spreading codes. User detection is achieved with time gating and nonlinear thresholding to suppress the multiaccess interference of other users. Incorporation of forward error correction successfully reduces the performance loss imposed by coherent beat interference, resulting in error-free performance (BER<10-11), significant per-user power penalty reduction, and the elimination of a bit-error-rate noise floor. The testbed also applies bandwidth suppression within the encoders and decoders, yielding a 52% increase in spectral efficiency

Efficient proving for practical distributed access-control systems

Abstract: We present a new technique for generating a formal proof that an access request satisfies access-control policy, for use in logic-based access-control frameworks. Our approach is tailored to settings where credentials needed to complete a proof might need to be obtained from, or reactively created by, distant components in a distributed system. In such contexts, our approach substantially improves upon previous proposals in both computation and communication costs, and better guides users to create the most appropriate credentials in those cases where needed credentials do not yet exist. At the same time, our strategy offers strictly superior proving ability, in the sense that it finds a proof in every case that previous approaches would (and more). We detail our method and evaluate an implementation of it using both policies in active use in an access-control testbed at our institution and larger policies indicative of a widespread deployment.