Collision avoidance for Delay_Req messages in broadcast media

The time accuracy of the Precision Time Protocol deteriorates in consequence to Delay req/Delay resp session collisions common for applications using shared broadcast media. In this paper we propose a protocol that coordinates Delay_req/Delay_resp sessions with minimum changes to the original PTP protocol. Simulations illustrate protocol’s operation and demonstrate significant reduction of session collisions

Automatic Segmentation of Posterior Pole Retinal Layers In Patients with Early Stage Glaucoma Using Spectral Domain Optical Coherence Tomography

Purpose: To measure Ganglion Cell Layer (GCL) and Retinal Nerve Fiber Layer (RNFL) thickness of the retinal posterior pole in patients with early stage primary open-angle glaucoma (POAG) using the new automatic segmentation technology of spectral domain optical coherence tomograph (SD-OCT). Methods: 37 clinical records of patients with early glaucoma (grade 1 to 2 according to the Glaucoma Staging System 2) and 40 age and sex-matched controls were considered in this case-control observational retrospective study. Automated segmentation of GCL and RNFL was performed in one randomly selected eye from the electronic OCT records of each participant using the new Spectralis SD-OCT segmentation technology (Heidelberg Engineering, Inc., Heidelberg, Germany). Thickness of different retinal layers was obtained from each Posterior Pole volumetric scan. Measurements of the peripapillary RNFL thickness (pRNFLt) were also obtained and then compared with those of posterior pole RNFL thickness (ppRNFLt). Results: Both GCL and RNFL were significantly thinner at the retinal posterior pole in the POAG group as compared to the control group (p<0,0001). Furthermore, pRNFLt was significantly thinner in the glaucoma group as opposed to the control group (p<0,0001). Measurements of pRNFLt were significantly correlated with those of the ppRNFLt (Pearson’s coefficient r=0.863). Conclusions: The new Spectralis SD-OCT automatic segmentation tool may be useful in evaluating structural damage in patients with early glaucoma, by providing complementary measurements to the clinical assessment of glaucoma that could be used in conjunction with other relevant parameters in the diagnosis and the evaluation of the progression of the disease

Teaching Networks to Digital Humanists

Contribution: A technical course in a multidisciplinary university program has to provide high-level skills, with limited lecturing hours and student background. This article investigates the principles for its design and reports about a study case. Background: The overall course organization needs to address specific learning targets and teaching techniques, different from those used in traditional courses on the topic. Research Question: A stepwise strategy assists a principled design that allows dynamic, long-term improvements. Methodology: The evaluation of its applicability requires a years-long record of historical data. The article studies the evolution of a course over six years using simple monitoring techniques: surveys and rubric-based examinations. Findings: Monitoring emerges as an essential feature for course evolution: a focused examination provides the best results, while institutional, wide-spectrum surveys appear to be of little help

Beyond Nagios - Design of a cloud monitoring system

The paper describes a monitoring system specially designed for cloud infrastructures. The features that are relevant for such distributed application are -) scalability, that allows utilization in systems of thousands of nodes, -) flexibility, to be customized for a large number of applications, -) openness, to allow the coexistence of user and administration monitoring. We take as a starting point the Nagios monitoring system, that has been successfully used for Grid monitoring and is still used for clouds. We analyze its shortcomings when applied to cloud monitoring, and propose a new monitoring system, that we call Rocmon, that sums up Nagios experience with a cloud perspective. Like Nagios, Rocmon is plugin-oriented to be flexible. To be fully inter-operable and long-living, it uses standard tools: the OGF OCCI for the configuration interface, the REST paradigm to take advantage of Web tools, and HTML5 WebSockets for data transfers. The design is checked with an open source Ruby implementation featuring the most relevant aspects

Improving the Utilization of an Elastic Resource: A Client-side Approach

Resource management is traditionally addressed by policies implemented inside the resource provider. Here we study the problem with an attitude that is specular but complementary, which consists in designing a distributed client-side access regulation algorithm that improves the utilization of an elastic resource. The introduction of elastic resources — a feature of the cloud computing paradigm — complicates their management since, when the workload applied on the resource varies (for instance with the number of users) the resource automatically follows such variations with its capacity. But the presence of an extra computational cost related with capacity variations motivates a non linear, lazy response, that penalizes dynamic environments. Hence the interest for an algorithm that shapes the production of service requests on the client side. To make our investigation more adherent to a practical environment, we introduce a real time requirement: each client must have access to the service at least every π time units. Examples of this requirement, that features a bounded degree of asynchrony, are found, for instance, in network streaming applications: stream chunks must feed the input buffer at the destination. The algorithm we investigate is based on the random walk of a token. To evaluate the range of applicability of the algorithm, we define an analytic model of its stochastic behavior — described by a non-Markov process — and then we compare its performance with a benchmark algorithm, representative of an effective solution that is often used in practice

Teaching networks in the cloud

The Web is populated by a growing number of services that provide access to remote IT resources: they are col- lectively addressed as the Cloud. Such incoherent and expanding number of services is investigated to find those that can help the task of teaching, focusing on a challenging case study for which I have a direct experience: a course in computer networks with the purpose of giving the students a hands-on experience using production-grade techniques. The outcome of the case study is that on-line services can complement traditional frontal lectures, to enrich the communi- cation between the teacher and the student, and to improve the learning experience. This is a hint for teachers, and characterizes a potential market for developers and providers

Application level interface for a cloud monitoring service

We introduce a new paradigm, based on an extension of the Open Cloud Computing Interface (OCCI), for the on demand monitoring of the cloud resources provided to a user. We have extended the OCCI with two new sub-types of core entities: one to collect the measurements, and the other to process them. The user can request instances of such entities to implement a monitoring infrastructure. The paradigm does not target a specific cloud model, and is therefore applicable to any kind of resource provided as a service. The specifications include only the minimum needed to describe a monitoring infrastructure, thus making this standard extension simple and easily adoptable. Despite its simplicity the model is able to describe complex solutions, including private/public clouds, and covers both infrastructure and application monitoring. To highlight the impact of our proposal in practice, we have designed an engine that deploys a monitoring infrastructure using its OCCI-compliant descriptions. The design is implemented in a prototype that is available as open source