Antonio Robles-Gómez

Open Service-Oriented Platforms for Personal Learning Environments

Learning management systems (LMSs) are software systems for administrating, tracking, and reporting on e-learning programs. The authors next-generation LMS provides a personal learning environment (PLE) in which LMS functions are integrated into a context that users are familiar with and use for other purposes - that is, mashup platforms using gadgets. By modularizing LMS functionality as a collection of services, the system lets users select just those services they want, use services from multiple providers, and mix their learning with other activities in a more natural manner. The authors deployed and tested their system at the Spanish University for Distance Education, which has a virtual campus of more than 200,000 students. Their survey indicates that the system is useful and easy to use for building individualized PLEs.

Deadlock-Free Dynamic Network Reconfiguration Based on Close Up*/Down* Graphs

Current high-performance distributed systems use a switch-based interconnection network. After the occurrence of a topological change, a management mechanism must reestablish connectivity between network devices. This mechanism discovers the new topology, calculates a new set of routing paths, and updates the routing tables within the network. The main challenge related to network reconfiguration (the change-over from one routing function to another) is avoiding deadlocks. Former reconfiguration techniques significantly reduce network service. In addition, most recent proposals either need extra network resources (such as virtual channels) or their computation complexities are prohibitive. For up*/down* routed networks we propose a new reconfiguration method that supports a virtually unaffected network service at a minor computational cost. This method is suitable for both source and distributed routing networks, and does neither restrict the injection of packets nor the updating of routing tables during the topology-change assimilation.

Implementing the Advanced Switching Fabric Discovery Process

Advanced switching is a new high-speed industrial standard serial interconnect. It is defined as a switching fabric architecture based on the PCI express technology. The advanced switching specification establishes a management infrastructure which maintains the fabric operation. The topology discovery process is triggered after fabric initialization and every time a topological change is detected. The information gathered by this process is used to build a set of paths between fabric endpoints. This work analyzes the performance of several possible implementations for this management task.

A Deadlock-Free Dynamic Reconfiguration Scheme for Source Routing Networks Using Close Up*/Down* Graphs

Computer performance has significantly increased in recent years and, consequently, communication subsystems have become bottlenecks within systems. To counter this problem, current high-performance distributed systems employ switch-based interconnection networks. In this scenario, after the occurrence of a topological change, a management mechanism must reestablish connectivity between network devices. This requires performing a network reconfiguration, which consists in updating the routing function. The main challenge involved in network reconfiguration is the reduction of performance degradation during the change assimilation process. As shown in the performance evaluation section, former reconfiguration techniques significantly reduce network service since the application traffic is temporally stopped in order to avoid deadlocks. In addition, current solutions are only designed for networks that use distributed routing. In this paper, we propose and evaluate a first reconfiguration method for source routing networks that does not restrict the injection of packets during the change assimilation process. Without requiring additional network resources, our scheme is able to recover topology connectivity maintaining network throughput.

A model for the development of AS fabric management protocols

Advanced Switching (AS) is a switching fabric architecture based on the PCI Express technology. In order to support high availability, AS includes important features, such as device hot addition and removal, redundant pathways, and fabric management failover. This work presents an AS model developed in OPNET. The contribution of this tool is that it can help researchers to design and evaluate management mechanisms for this new technology. It can also be used to analyze other key aspects of the architecture, such as routing, congestion, and quality of service.

P2P-based resource discovery in dynamic grids allowing multi-attribute and range queries

A key point for the efficient use of large grid systems is the discovery of resources, and this task becomes more complicated as the size of the system grows up. In this case, large amounts of information on the available resources must be stored and kept up-to-date along the system so that it can be queried by users to find resources meeting specific requirements (e.g. a given operating system or available memory). Thus, three tasks must be performed, (1) information on resources must be gathered and processed, (2) such processed information has to be disseminated over the system, and (3) upon users requests, the system must be able to discover resources meeting some requirements using the processed information. This paper presents a new technique for the discovery of resources in grids which can be used in the case of multi-attribute (e.g. {OS=Linux &memory=4GB}) and range queries (e.g. {50GB

A proposal for managing ASI fabrics

Recent years, computer performance has been significantly increased. As a consequence, data I/O systems have become bottlenecks within systems. To alleviate this problem, Advanced Switching was recently proposed as a new standard for future interconnects. The Advanced Switching specification establishes a fabric management infrastructure, which is in charge of updating the set of fabric paths each time a topological change takes place. The use of source routing and passive switches makes unfeasible the adaptation to this new technology of many existing proposals to handle topological changes in switched interconnection networks. This paper presents a fabric management mechanism for Advanced Switching, but also suitable for other source routing interconnects. Furthermore, the work presents a detailed performance evaluation for this proposal. This evaluation allows us to identify the main drawbacks of the mechanism and to define future improvements.

A new distributed management mechanism for ASI based networks

Advanced Switching Interconnect (ASI) is a high-speed serial interconnect embodied in the Dolphin Express family of interconnect products. In order to support high availability, the ASI specification established a management infrastructure, which is in charge of maintaining network operation after the occurrence of a topological change. When such a change occurs, the management mechanism discovers the new topology, calculates a set of valid routing paths, and distributes them to endpoints within the fabric. Several implementations for such a management mechanism have been proposed that use a centralized approach. These solutions can have negative effects with respect to network service availability. With the aim of eliminating these potential negative effects, this paper proposes a distributed solution for the computation of new paths. The distributed solution is evaluated for management entities with different performance capabilities, and for a range of traffic patterns and load levels. Our results show that the new distributed solution significantly reduces the change assimilation time and the negative impact on the network service when it is compared to a centralized solution.

A Complete Topology Management Mechanism for the Advanced Switching Interconnect Technology

The advanced switching technology is a new high-performance standard serial inter-connect. Its specification establishes a management infrastructure in charge of maintaining the fabric operation after the occurrence of a topological change. When the change is detected, the management mechanism discovers the new topology, obtains a set of fabric paths, and finally distributes them to the endpoints. The main contribution of this paper is a completely functional mechanism that implements all these management tasks involved in handling topological changes in source routing switched networks, as advanced switching. We also analyze the behavior of this first proposal, in order to identify its bottlenecks and define future improvements.

Efficient and deadlock-free reconfiguration for source routed networks

Overlapping Reconfiguration is currently the most efficient method to reconfigure an interconnection network, but is only valid for systems that apply distributed routing. This paper proposes a solution which enables utilization of Overlapping Reconfiguration in a source routed environment. We demonstrate how a synchronized injection of tokens has a significant impact on the performance of the method. Furthermore, we propose and evaluate an optimization of the original algorithm that reduces (and in some cases even eliminates) performance issues caused by the token forwarding regime, such as increased latency and decreased throughput.