CAC controlled services sharing a link with connectionless data services in an ATM network: a performance evaluation study

In the B-ISDN there is a provision for four classes of services, all of them supported by a single transport network (the ATM network). Three of these services, the connected oriented (CO) ones, permit connection access control (CAC) but the fourth, the connectionless oriented (CLO) one, does not. Therefore, when CLO service and CO services have to share the same ATM link, a conflict may arise. This is because a bandwidth allocation to obtain maximum statistical gain can damage the contracted ATM quality of service (QOS); and vice versa, in order to guarantee the contracted QOS, the statistical gain have to be sacrificed. The paper presents a performance evaluation study of the influence of the CLO service on a CO service (a circuit emulation service or a variable bit-rate service) when sharing the same link

Resource dimensioning aspect of heterogeneous traffic with different service requirements: Integration versus segregation

In this paper, we consider the ATM networks in which the virtual path concept is implemented. The question of how to multiplex two or more diverse traffic classes while providing different quality of service requirements is a very complicated open problem. Two distinct options are available: integration and segregation. In an integration approach all the traffic from different connections are multiplexed onto one VP. This implies that the most restrictive QOS requirements must be applied to all services. Therefore, link utilization will be decreased because unnecessarily stringent QOS is provided to all connections. With the segregation approach the problem can be much simplified if different types of traffic are separated by assigning a VP with dedicated resources (buffers and links). Therefore, resources may not be efficiently utilized because no sharing of bandwidth can take place across the VP. The probability that the bandwidth required by the accepted connections exceeds the capacity of the link is evaluated with the probability of congestion (PC). Since the PC can be expressed as the CLP, we shall simply carry out bandwidth allocation using the PC. We first focus on the influence of some parameters (CLP, bit rate and burstiness) on the capacity required by a VP supporting a single traffic class using the new convolution approach. Numerical results are presented both to compare the required capacity and to observe which conditions under each approach are preferred

Bandwidth allocation based on real time calculations using the convolution approach

This paper focuses on one of the methods for bandwidth allocation in an ATM network: the convolution approach. The convolution approach permits an accurate study of the system load in statistical terms by accumulated calculations, since probabilistic results of the bandwidth allocation can be obtained. Nevertheless, the convolution approach has a high cost in terms of calculation and storage requirements. This aspect makes real-time calculations difficult, so many authors do not consider this approach. With the aim of reducing the cost we propose to use the multinomial distribution function: the enhanced convolution approach (ECA). This permits direct computation of the associated probabilities of the instantaneous bandwidth requirements and makes a simple deconvolution process possible. The ECA is used in connection acceptance control, and some results are presented

Multicast algorithms evaluation using an adaptative routing in ATM networks

This paper proposes a multicast implementation based on adaptive routing with anticipated calculation. Three different cost measures for a point-to-multipoint connection: bandwidth cost, connection establishment cost and switching cost can be considered. The application of the method based on pre-evaluated routing tables makes possible the reduction of bandwidth cost and connection establishment cost individually

Automatic self-configuration of the logical network using distributed software agents

We present a system for dynamic network resource configuration in environments with bandwidth reservation. The proposed system is completely distributed and automates the mechanisms for adapting the logical network to the offered load. The system is able to manage dynamically a logical network such as a virtual path network in ATM or a label switched path network in MPLS or GMPLS. The system design and implementation is based on a multi-agent system (MAS) which make the decisions of when and how to change a logical path. Despite the lack of a centralised global network view, results show that MAS manages the network resources effectively, reducing the connection blocking probability and, therefore, achieving better utilisation of network resources. We also include details of its architecture and implementation

An improved method for discovering link criticality in transport networks

Quantitatively assessing the importance or criticality of each link in a network is of practical value to operators, as that can help them to increase the network's resilience, provide more efficient services, or improve some other aspect of the service. Betweenness is a graph-theoretical measure of centrality that can be applied to communication networks to evaluate link importance. However, as we illustrate in this paper, the basic definition of betweenness centrality produces inaccurate estimations as it does not take into account some aspects relevant to networking, such as the heterogeneity in link capacity or the difference between node-pairs in their contribution to the total traffic. A new algorithm for discovering link centrality in transport networks is proposed in this paper. It requires only static or semi-static network and topology attributes, and yet produces estimations of good accuracy, as verified through extensive simulations. Its potential value is demonstrated by an example application. In the example, the simple shortest-path routing algorithm is improved in such a way that it outperforms other more advanced algorithms in terms of blocking ratio

Lightweight monitoring of label switched paths for bandwidth management

The purpose of resource management is the efficient and effective use of network resources, for instance bandwidth. In this article, a connection oriented network scenario is considered, where a certain amount of bandwidth is reserved for each label switch path (LSP), which is a logical path, in a MPLS or GMPLS environment. Assuming there is also some kind of admission control (explicit or implicit), these environments typically provide quality of service (QoS) guarantees. It could happen that some LSPs become busy, thus rejecting connections, while other LSPs may be under-utilised. We propose a distributed lightweight monitoring technique, based on threshold values, the objective of which is to detect congestion when it occurs in an LSP and activate the corresponding alarm which will trigger a dynamic bandwidth reallocation mechanism

Dynamic bandwidth management as part of an integrated network management system based on distributed agents

We present a system for dynamic network resource configuration in environments with bandwidth reservation and path restoration mechanisms. Our focus is on the dynamic bandwidth management results, although the main goal of the system is the integration of the different mechanisms that manage the reserved paths (bandwidth, restoration, and spare capacity planning). The objective is to avoid conflicts between these mechanisms. The system is able to dynamically manage a logical network such as a virtual path network in ATM or a label switch path network in MPLS. This system has been designed to be modular in the sense that in can be activated or deactivated, and it can be applied only in a sub-network. The system design and implementation is based on a multi-agent system (MAS). We also included details of its architecture and implementation

Mestre educació musical: ampliació de coneixements. Obertura a altres sistemes educatius. Exposició, reflexió i valoració de l’experiència

La implantació del pla d’estudis de 1992, suposà un canvi en els estudis de mestre i l’aparició de l’especialitat d’educació musical. Conseqüentment, la didàctica aplicada als estudis de música va propiciar que volguéssim conèixer la font de la metodologia musical més arrelada a casa nostra després de l’adaptació del mètode Kódaly (Hongria) que el P. Ireneu Segarra, monjo de Montserrat, va fer a Catalunya. L’interès venia donat per conèixer de primera mà una de les propostes formatives més difoses a l’ensenyament primari. L’èxit d’aquesta primera experiència realitzada el 1994 ens va portar a fer una planificació d’altres possibles llocs d’interès, bé per les seves metodologies, bé per la cultura musical pròpia. Això va donar lloc a realitzar visites a institucions educatives de França (París, 1999), Suïssa (Ginebra, 2000 i 2007), Àustria (Salzburg, 2001 i 2009), Hongria (Kescskemet, 2002), Bèlgica (Namur, 2003), Itàlia (Bologna i Milano, 2004), i Anglaterra (Reading, Oxford i Cambridge 2005)

La gestió pública i privada dels espais esportius a les comunitats autònomes i els sistemes locals.

Resumen tomado del autor. Aparecen tablas de datos

Els sistemes de formació reglada i no reglada com a opcions de futur professional. 'Los sistemas de formación reglada y no reglada como opciones de futuro profesional'.

Resumen tomado parcialmente de la propia revista

Escolarització i dinàmica de sistemes. 'Escolarización y dinámica de sistemas'.

Se analiza el fenómeno de la escolarización en el ámbito internacional, como fenómeno en general: el conocimiento de la clase como sistema escolar, su estructura y su funcionamiento. Se han analizado todos los paises que en 1980 tenían más de 200.000 habitantes y, a partir de la Clasificación Internacional Normalizada de Educación (CINE) de la Unesco, se ha construído un modelo de simulación de las relaciones del sistema escolar con su entorno con la intención de explorar la dinámica del sistema. Se trata de un modelo matemático de simulación que permite confrontar los datos empíricos para un ulterior perfeccionamiento del sistema. Finalmente, a partir del diagrama causal, se presenta un modelo de dinámica de sistemas de la escolarización (MDS), denominado SCOLA.

Una nova eina didàctica en el laboratori de ciències experimentals : els sistemes informàtics d'adquisició i tractament de dades. 'Una nueva herramienta didáctica en el laboratorio de ciencias experimentales : los sistemas informáticos de adquisición y tratamiento de datos'.

Resumen de la autora en catalán

Els sistemes d'adquisició, tractament i control de dades. 'Los sistemas de adquisición, tratamiento y control de datos' ; Una nova tecnologia com eina didàctica de ciències experimentals. 'Una nueva tecnología como herramienta didáctica de ciencias experimentales'.

Resumen basado en el de la autora

Resolució de problemes de matemàtiques : identificació, origen i formació dels sistemes de creences en l'alumnat, alguns efectes sobre l'abordatge dels problemes. 'Resolución de problemas de matemáticas : identificación, orígen y formación de los sistemas de creencias en el alumnado, algunos efectos sobre el abordaje los problemas'.

Identificar elementos del sistema de creencias (SC) entorno a la actividad de resolución de problemas (RP), analizar la relación entre aquellos y las acciones desarrolladas durante el abordaje en la RP no estándar e identificar aspectos que incidan en el origen y formación de los SC. Todo el alumnado de primero de ESO de un centro para el estudio de grupo y 8 alumnos para el estudio de casos. El estudio integra el enfoque cuantitativo con un estudio de grupo y el enfoque cualitivo con un estudio de casos, integrando a la vez en cada uno de ellos diferentes métodos de recogida de datos. Se utilizan como instrumentos principales de análisis la potencia de las creencias (centralidad psicológica) y los mapas (conexiones y estructura en general). Los resultados (estructura del SC) han permitido concluir que el alumnado caracteriza el ÷problema de matemáticas como una categoría de pregunta escolar, de naturaleza aritmética, que viene caracterizada por aspectos formales de presentación, sin ninguna referencia ni a los conocimientos del resolutor ni a la finalidad con la cual se propone. También se concluye que se caracteriza la RP como una actividad de reconocimiento/ aplicación y a la vez de acreditación de las técnicas aprendidas en clase. En cuanto a los esquemas de actuación desarrollados en la fase de abordaje de problemas no estándar, los más frecuentemente observados son los descritos como ingenuos, impulsivos o irreflexivos, y los consistentes en dar respuesta rápida, incluso entre el alumnado con mayor rendimiento académico, describiéndose a la vez relevantes relaciones entre estos esquemas y elementos de su SC. En cuanto al orígen de estos SC, se han descrito relaciones entre su proceso de formación y aspectos del propio contexto escolar (tareas rutinarias, trabajo con RP claramente diferenciado de lo habitual, papel jugado por el profesorado), aspectos externos al contexto escolar (presiones y experiencias compartidas con familiares, mitos sociales) y algunos aspectos afectivos.