Robert G. Cole

Voice over IP performance monitoring

We describe a method for monitoring Voice over IP (VoIP) applications based upon a reduction of the ITU-Ts E-Model to transport level, measurable quantities. In the process, 1) we identify the relevant transport level quantities, 2) we discuss the tradeoffs between placing the monitors within the VoIP gateways versus placement of the monitors within the transport path, and 3) we identify several areas where further work and consensus within the industry are required. We discover that the relevant transport level quantities are the delay, network packet loss and the decoders de-jitter buffer packet loss. We find that an in-path monitor requires the definition of a reference de-jitter buffer implementation to estimate voice quality based upon observed transport measurements. Finally, we suggest that more studies are required, which evaluate the quality of various VoIP codecs in the presence of representative packet loss patterns.

Spinal stenosis prevalence and association with symptoms: the Framingham Study

BACKGROUND CONTEXT The prevalence of lumbar spinal stenosis (LSS) in the general population and association with low back pain (LBP) remain unclear. PURPOSE To evaluate the prevalence of congenital and acquired LSS observed on computed tomography in a community-based sample; and to evaluate the association between LSS and LBP. STUDY DESIGN/SETTING Cross-sectional observational study. This study was an ancillary project to the Framingham Heart Study. PATIENT SAMPLE A total of 3,529 participants underwent multidetector computed tomography; 191 were enrolled in this study. OUTCOME MEASURES Self-report measures: LBP in the preceding 12 months was evaluated using a self-report questionnaire. Physiologic measures: LSS (congenital and acquired) was characterized using two cut-points: 12mm for relative LSS and 10mm for absolute LSS. METHODS Using multiple logistic regression, we examined the association between LSS and LBP, adjusting for sex, age, and body mass index. RESULTS In the congenital group, relative LSS was found in 4.7% and absolute LSS in 2.6% of patients. Acquired LSS was found in 22.5% and in 7.3%, respectively. Acquired LSS showed increasing prevalence with age less than 40 years, the prevalence of relative and absolute LSS was 20.0% and 4.0%, respectively, and in those 60 to 69 years the prevalence was 47.2% and 19.4%, respectively. The presence of absolute LSS was associated with LBP with an odds ratio of 3.16 (95% confidence interval [CI]: 1.05-9.53). CONCLUSIONS The prevalence of congenital and acquired LSS in a community-based sample was characterized. The prevalence of acquired stenosis increased with age. LSS is associated with a threefold higher risk of experiencing LBP.

Facet joint osteoarthritis and low back pain in the community-based population.

Study Design. Cross-sectional study. Objective. To evaluate the association between lumbar spine facet joint osteoarthritis (FJ OA) identified by multidetector computed tomography (CT) and low back pain (LBP) in the community-based Framingham Heart Study. Summary of Background Data. The association between lumbar FJ OA and LBP remains unclear. Methods. This study was an ancillary project to the Framingham Heart Study. A sample of 3529 participants of the Framingham Heart Study aged 40 to 80 underwent multidetector CT imaging to assess aortic calcification. One hundred eighty-eight individuals were consecutively enrolled in this ancillary study to assess radiographic features associated with LBP. LBP in the preceding 12 months was evaluated using a self-report questionnaire. FJ OA was evaluated on CT scans using a 4-grade scale. The association between FJ OA and LBP was examined used multiple logistic regression models, while adjusting for gender, age, and BMI. Results. CT imaging revealed a high prevalence of FJ OA (59.6% of males and 66.7% of females). Prevalence of FJ OA increases with age. By decade, FJ OA was present in 24.0% of <40-years-olds, 44.7% of 40- to 49-years-olds, 74.2% of 50- to 59-years-olds, 89.2% of 60- to 69-year-olds, and 69.2% of >70-years-olds. By spinal level the prevalence of FJ OA was: 15.1% at L2–L3, 30.6% at L3–L4, 45.1% at L4–L5, and 38.2% at L5–S1. In this community-based population, individuals with FJ OA at any spinal level showed no association with LBP. Conclusion. There is a high prevalence of FJ OA in the community. Prevalence of FJ OA increases with age with the highest prevalence at the L4–L5 spinal level. At low spinal levels women have a higher prevalence of lumbar FJ OA than men. In the present study, we failed to find an association between FJ OA, identified by multidetector CT, at any spinal level and LBP in a community-based study population.

A kinetic theory calculation of the orientational correlation time of a rotorlike molecule in a dense fluid of spheres

The collective and single‐particle orientational correlation times are calculated using Boltzmann–Enskog kinetic theory for N rotorlike molecules in a bath of spheres. By assuming that the rotors and bath are hard convex bodies, the collision integrals can be reduced exactly to one‐ and two‐dimensional integrals, which are then readily amenable to numerical quadrature. The calculated correlation times depend on density and temperature in the same way as do the rough hard sphere results. However, the particle shape anisotropy plays the role of the roughness parameters. Comparison of the collective and single‐particle orientational correlation times with experiment (including molecular dynamics) indicates that the kinetic theory consistently neglects part of the frictional drag. In all cases studied, the calculated times were a factor of 2 to 4 below the experimental values.

A renormalized kinetic theory of dilute molecular gases: Chattering

The phenomenon of molecular chattering (a collision between two rigid ovaloids involving two or more impulsive hits) is investigated with emphasis on the importance of these collisions on kinetic theory calculations for dilute molecular systems. To facilitate this analysis, the pseudo‐Liouville formalism, commonly employed in the kinetic theory of rigid spheres, is generalized to a form appropriate to rigid ovaloids. From this formalism, we derive a chattering expansion of the bracket integrals, the terms of which successively incorporate higher order chattering sequences. Finally, the results of scattering trajectories between a rigid sphere and a rigid ellipsoid are reported. It is demonstrated that the neglect of chattering sequences leads to large errors when calculating the bracket integrals for realistic model parameters; the errors ranging from ∼1% to as high as ∼200%.

Monitoring for security intrusion using performance signatures

A new approach for detecting security attacks on software systems by monitoring the software system performance signatures is introduced. We present a proposed architecture for security intrusion detection using off-the-shelf security monitoring tools and performance signatures. Our approach relies on the assumption that the performance signature of the well-behaved system can be measured and that the performance signature of several types of attacks can be identified. This assumption has been validated for operations support systems that are used to monitor large infrastructures and receive aggregated traffic that is periodic in nature. Examples of such infrastructures include telecommunications systems, transportation systems and power generation systems. In addition, significant deviation from well-behaved system performance signatures can be used to trigger alerts about new types of security attacks. We used a custom performance benchmark and five types of security attacks to derive performance signatures for the normal mode of operation and the security attack mode of operation. We observed that one of the types of the security attacks went undetected by the off-the-shelf security monitoring tools but was detected by our approach of monitoring performance signatures. We conclude that an architecture for security intrusion detection can be effectively complemented by monitoring of performance signatures.

Kinetic theory of the depolarized light scattering R parameter. I. Formal theory

The R parameter, which measures the magnitude of the Rytov dip observed in light scattering spectra, is calculated using kinetic theory for a dense, neat fluid of hard ellipsoids (rotors). The kinetic theory truncates the BBGKY hierarchy at the Enskog level and ignores chattering events when determining two body dynamics. As such, this theory represents an extension of our earlier work on the collective and single particle orientational correlation times of rotor‐like molecules.

Beacon-Based Routing for Tactical Networks

The U.S. Department of Defenses (DoD) warfighter is reliant upon the development of a reliable, resilient communications capability under harsh, battlefield environments. Due to high mobilities and the nature of the various terrains, the dynamics of the communications links is extremely erratic and rapidly changing. This results in extreme strain on the performance of routing protocols attempting to find and maintain viable communications paths. In this paper we discuss and analyze a new class of routing protocols which we refer to as Beacon-Based Routing protocols. Beacon-Based Routing protocols proactivity build a small number of, typically one or two, spanning trees in the network and use these trees to discover paths on demand. The existence of one (or more) spanning tree(s) ensures full network connectivity and hence can be used to find network paths without the need for network-wide broadcast of discovery messages, as in other on-demand routing protocols. This class of routing protocols represents the generalization of the Pulse Protocol [1], originally developed in 2002 for applications to Internet access networks. The performance of the Pulse Protocol was analyzed in [1] and [2] in various applications including general Mobile Ad-Hoc Networks (MANETs) and in sensor networks. As we discuss in this paper, the Beacon-Based Routing protocol class has optimal behavior with respect to the communications overhead required to run the protocol. As such, its scaling behavior is superior to other existing routing protocol classes when assessed in the context of a MANET.

Implications of Precedence and Preemption Requirements on Packet Based Transport Architectures

Over the last several years there have been various attempts to extend traditional Precedence enabled transport services to support all Command and Control (C2) applications. Traditional experience with Precedence based transport services support either circuit-switched, voice-based transport, e.g., the Defense Switched Network (DSN), or message-switched transport, e.g., the Defense Message System (DMS) and the Automated Message Handling System (AMHS). We believe these attempts to extend and define new Precedence enabled transport services have failed because of a lack of well defined requirements and an understanding of their implications. In this paper, we offer a core set of ten requirements for Precedence and Preemption enabled transport services which aim to support all C2 applications. We make no claim as to the originality of these requirements; others have proposed subsets of these in the past. Based upon these ten requirements, we then discuss and identify their implications on network architectures for packet-based transport services. In the process we hope to better clarify the implications of the requirements and the network mechanisms to be designed and developed for future military Precedence enabled communications networks. We conclude by identifying areas for future research and development in order to bring packet-based Precedence-enabled transport services to all C2 applications.

An investigative analysis of information assurance issues associated with the GIG's P&P architecture

The Global Information Grid (GIG) is a collection of systems, programs and initiatives aimed at building a secure network and set of information capabilities modeled after the Internet. The GIG is expected to facilitate DoDs transformation by allowing warfighters, policy makers and support personnel to engage in rapid decision making. The roadmap is designed to take advantage of converged services of voice, data, video, and imagery over common data links. The vision is to have commanders identify threats more effectively, make informed decisions, and respond with greater precision and lethality. The information advantage gained through the GIG and network-centric warfare (NCW) allows a warfighting force to achieve dramatically improved information positions, in the form of common operational pictures that provide the basis for shared situational awareness and knowledge, and a resulting increase in combat power. The GIG Precedence and Preemption (P&P) requirements stem from the need to utilize scarce resources at critical times in the most effective way in support of national security, the intelligence community and the war-fighter. Information Assurance (IA) enables all information and data to be available end-to-end to support any mission without delay in accordance to the sensitivity of the task. Together, P&P and IA ensure data availability integrity, authentication, confidentiality, and non-repudiation. This study addresses and analyzes the QoS and P & P requirements and architecture for the GIG. Threat scenarios are presented and used to evaluate the reference architectures. The goal of the study is to assess the Information Assurance concerns associated with implementing Precedence and Preemption within the GIG and to guarantee an acceptable minimum level of security and protection for DoD networks.