Teodor Jové

A review of the architecture of admission control schemes in the Internet

Admission Control (AC) is an efficient way of dealing with congestion situations in a network. Using AC, when network resources in a path are not enough for all flows (i.e., during congestion), some of the flows receive the requested service and the rest do not. Congestion situations can be reduced by increasing network resources or by optimizing their use through better routing techniques, but if congestion still occurs, AC achieves efficient use of network resources by maximizing the number of satisfied flows. However, using AC complicates the network scheme, and therefore a major concern is making the AC as simple as possible. In this paper we review the main AC schemes that have been proposed for the Internet, focusing on the simplicity of their architectures in terms of the number of nodes that participate in the AC, the required state, the use of signaling, and others.

Dynamic Branch Speculation in a Speculative Parallelization Architecture for Computer Clusters

This article describes a technique for path unfolding for conditional branches in parallel programs executed on clusters. Unfolding paths following control structures makes it possible to break the control dependencies existing in the code and consequently to obtain a high degree of parallelism through the use of idle CPUs. The main challenge of this technique is to deal with sequences of control statements. When a control statement appears in a path after a branch, a new conditional block needs to be opened, creating a new code split before the previous one is resolved. Such subsequent code splits increase the cost of speculation management, resulting in reduced profits. Several decision techniques have been developed for improving code splitting and speculation efficiency in single machine architecture. The main contribution of this paper is to apply such techniques to a cluster of single processor systems and evaluate them in such an environment. Our results demonstrate that code splitting in conjunction with branch speculation and the use of statistical information improves the performance measured by the number of processes executed in a time unit. This improvement is particularly significant when the parallelized programs contain iterative structures in which conditions are repeatedly executed. Copyright

Throughput guarantees for elastic flows using end-to-end admission control

Internet applications such as web or ftp will be satisfactorily supported by a guaranteed minimum throughput service. We propose to build this service in a core-stateless network such as Differentiated Services with an Admission Control (AC) method based on end-to-end measurements, using the first packets of the flow. The whole scheme uses a small set of packet classes (with different discarding priorities), and is therefore simple and scalable. We evaluate the scheme through simulations in several scenarios using TCP flows. Finally, we propose an extension of the method aimed at improving its performance.

Network schemes for TCP elastic traffic in the Internet

TCP elastic traffic is generated by the traditional “data” applications in the Internet, such as web browsing, peer-to-peer file sharing, ftp, e-mail and other. These applications are built on top of TCP, which provides reliable transfers and adjusts the sending rate to the network conditions to achieve the maximum possible throughput, a feature that makes TCP flows to be called “elastic”. From the point of view of the network, TCP elastic traffic requires the maximum possible throughput above a minimum value, a network service that we call the Minimum Throughput Service (MTS). In this paper we survey the main network schemes that have been proposed in the Internet to provide this service for TCP elastic traffic, classified in two broad groups, the ones that do not use Admission Control (AC) and the ones that do use it. For each network scheme we describe the main characteristics of the service (whether the minimum throughput can be different or is the same for all flows, whether isolation among flows is provided, etc.) and their architecture (the specific traffic conditioning, queue disciplines and AC mechanisms used, the required state, the use of signaling, etc.).

A guaranteed minimum throughput service for TCP flows using measurement‐based admission control

We propose a new scheme for a network service that guarantees a minimum throughput to flows accepted by admission control (AC). The whole scheme only uses a small set of packet classes in a core-stateless network. At the ingress of the network each flow packet is marked into one of the sets of classes, and within the network, each class is assigned a different discarding priority. The AC method is based on edge-to-edge per-flow throughput measurements using the first packets of the flow, and it requires flows to send with a minimum rate. We evaluate the scheme through simulations in a simple bottleneck topology with different traffic loads consisting of TCP flows that carry files of varying sizes. We use a modified TCP source with a new algorithm that forces the source to send with a minimum rate. We compare our scheme with the best-effort service and we study the influence of the measurement duration on the schemes performance. The results prove that the scheme guarantees the requested throughput to accepted flows and achieves a high utilization of network resources. Copyright

Throughput Guarantees for TCP Flows in a Network Based on Packet Classes Using Edge-to-Edge Per Flow Measurements

TCP flows generated by applications such as the Web or FTP require a minimum network throughput and can also benefit from an extra throughput due to their rate-adaptive algorithms. To build a guaranteed minimum throughput service, the authors propose a scheme with Admission Control (AC) using a small set of packet classes in a core-stateless network. At the ingress of the network, each flow packet is marked as one of the set of classes, and within the network, each class is assigned a different discarding priority. The AC method is based on edge-to-edge per flow measurements and requires flows to be sent at a minimum rate. The scheme is able to provide different minimum throughput to different users and protection against nonresponsive sources. The authors evaluate the scheme through simulation using different traffic loads consisting of TCP flows that carry files of varying sizes. In the simulation, TCP uses a new algorithm that forces the source to keep the short-term sending rate above a desired minimum rate. The authors study the influence of several parameters on the performance of the scheme in different network topologies. The results show that the scheme guarantees the requested throughput to accepted flows and achieves a high utilization of network resources, similar to the ideal results of a classical hop-by-hop AC.

A packet class-based scheme for providing throughput guarantees to TCP flows

TCP flows generated by applications such as the web or ftp require a minimum network throughput to satisfy users. To build this service, we propose a scheme with Admission Control (AC) using a small set of packet classes in a core-stateless network. At the ingress each flow packet is marked as one of the set of classes, and within the network, each class is assigned a different discarding priority. The AC method is based on edge-to-edge per-flow measurements, and it requires flows to be sent at a minimum rate. The scheme is able to provide different throughput to different flows and protection against non-responsive sources. We evaluate the scheme through simulation in several network topologies with different traffic loads consisting of TCP flows that carry files of varying sizes. In the simulation, TCP uses a new algorithm to keep the short-term sending rate above a minimum value. The results prove that the scheme guarantees the throughput to accepted flows and achieves high utilization of resources, similar to the ideal results of a classical hop-by-hop AC.

AdaptHAs: Adapting Theme and Activity Selections for a Co-creation Process for High Ability Students

High ability or gifted students with difficulties in learning? This is a statement that many people think is incoherent because of the characteristics of these students, but it is more common than we think. One way of helping high ability students to develop their skills and be more motivated about their learning process is to encourage them be more active in creating learning activities through a co-creation process. However, a co-creation process in itself is not enough and so it is important to ensure that the students are the real protagonists by adapting to their characteristics, interests, needs, goals, personalities, multiple intelligences and cognitive styles. This paper presents a theoretical proposal for such an adaptation.

Model for Sharing Knowledge in a Co-creation Process with High Ability Students

A way to motivate high ability students in their learning process is by involving them in the co-creation of educational material. In doing so, the knowledge gained from the ensuing interaction between the high ability students, their parents and teachers can be very useful because it not only enhances the co-creation process itself, but also the subsequent activities as they are able to be adjusted to the students’ particular needs and goals. This paper describes two parts of a Knowledge Management System that focuses on utilizing students’ personal interests and encouraging their active participation to make improvements to the co-creation process by sharing the responsibility for their learning materials. To achieve this, we propose and develop a knowledge model that can identify the knowledge used in a co-creation process. Based on this knowledge model, we present a Knowledge Management System design which considers processing, support and general informatic system components.

MODELO DE PERFILES DE ADAPTACIÓN EN EL PROCESO DE CO-CREACIÓN DE MATERIAL PARA ESTUDIANTES CON ALTAS CAPACIDADES.

Los estudiantes con altas capacidades pueden tener una creatividad innata, mayor rapidez para aprender, un coeficiente intelectual mas alto, entre otras caracteristicas. Pero ?Por que algunos tienen problemas con su bajo rendimiento academico? Unos autores creen que la solucion al problema es la motivacion. Dicha motivacion puede potenciarse involucrando al estudiante en la creacion de los materiales educativos, que a su vez deben estar contextualizados en sus caracteristicas y en su realidad. Este articulo expone las ideas del diseno de un modelo de perfiles que soporta un proceso adaptativo de co-creacion de material educativo con base en las caracteristicas de los estudiantes con altas capacidades y de algunos modelos de ensenanza-aprendizaje. Ademas, se explica como se incluye la participacion del mismo estudiante, de su familia y de su profesor en el proceso de co-creacion del material.