New fault-tolerant routing algorithms for k-ary n-cube networks

The interconnection network is one of the most crucial components in a multicomputer as it greatly influences the overall system performance. Networks belonging to the family of k-ary n-cubes (e.g., tori and hypercubes) have been widely adopted in practical machines due to their desirable properties, including a low diameter, symmetry, regularity, and ability to exploit communication locality found in many real-world parallel applications. A routing algorithm specifies how a message selects a path to cross from source to destination, and has great impact on network performance. Routing in fault-free networks has been extensively studied in the past. As the network size scales up the probability of processor and link failure also increases. It is therefore essential to design fault-tolerant routing algorithms that allow messages to reach their destinations even in the presence of faulty components (links and nodes). Although many fault-tolerant routing algorithms have been proposed for common multicomputer networks, e.g. hypercubes and meshes, little research has been devoted to developing fault-tolerant routing for well-known versions of k-ary n-cubes, such as 2 and 3- dimensional tori. Previous work on fault-tolerant routing has focused on designing algorithms with strict conditions imposed on the number of faulty components (nodes and links) or their locations in the network. Most existing fault-tolerant routing algorithms have assumed that a node knows either only the status of its neighbours (such a model is called local-information-based) or the status of all nodes (global-information-based). The main challenge is to devise a simple and efficient way of representing limited global fault information that allows optimal or near-optimal fault-tolerant routing. This thesis proposes two new limited-global-information-based fault-tolerant routing algorithms for k-ary n-cubes, namely the unsafety vectors and probability vectors algorithms. While the first algorithm uses a deterministic approach, which has been widely employed by other existing algorithms, the second algorithm is the first that uses probability-based fault- tolerant routing. These two algorithms have two important advantages over those already existing in the relevant literature. Both algorithms ensure fault-tolerance under relaxed assumptions, regarding the number of faulty components and their locations in the network. Furthermore, the new algorithms are more general in that they can easily be adapted to different topologies, including those that belong to the family of k-ary n-cubes (e.g. tori and hypercubes) and those that do not (e.g., generalised hypercubes and meshes). Since very little work has considered fault-tolerant routing in k-ary n-cubes, this study compares the relative performance merits of the two proposed algorithms, the unsafety and probability vectors, on these networks. The results reveal that for practical number of faulty nodes, both algorithms achieve good performance levels. However, the probability vectors algorithm has the advantage of being simpler to implement. Since previous research has focused mostly on the hypercube, this study adapts the new algorithms to the hypercube in order to conduct a comparative study against the recently proposed safety vectors algorithm. Results from extensive simulation experiments demonstrate that our algorithms exhibit superior performance in terms of reachability (chances of a message reaching its destination), deviation from optimality (average difference between minimum distance and actual routing distance), and looping (chances of a message continuously looping in the network without reaching destination) to the safety vectors

Efficient mechanisms to provide fault tolerance in interconnection networks for pc clusters

Actualmente, los clusters de PC son un alternativa rentable a los computadores paralelos. En estos sistemas, miles de componentes (procesadores y/o discos duros) se conectan a través de redes de interconexión de altas prestaciones. Entre las tecnologías de red actualmente disponibles para construir clusters, InfiniBand (IBA) ha emergido como un nuevo estándar de interconexión para clusters. De hecho, ha sido adoptado por muchos de los sistemas más potentes construidos actualmente (lista top500). A medida que el número de nodos aumenta en estos sistemas, la red de interconexión también crece. Junto con el aumento del número de componentes la probabilidad de averías aumenta dramáticamente, y así, la tolerancia a fallos en el sistema en general, y de la red de interconexión en particular, se convierte en una necesidad. Desafortunadamente, la mayor parte de las estrategias de encaminamiento tolerantes a fallos propuestas para los computadores masivamente paralelos no pueden ser aplicadas porque el encaminamiento y las transiciones de canal virtual son deterministas en IBA, lo que impide que los paquetes eviten los fallos. Por lo tanto, son necesarias nuevas estrategias para tolerar fallos. Por ello, esta tesis se centra en proporcionar los niveles adecuados de tolerancia a fallos a los clusters de PC, y en particular a las redes IBA. En esta tesis proponemos y evaluamos varios mecanismos adecuados para las redes de interconexión para clusters. El primer mecanismo para proporcionar tolerancia a fallos en IBA (al que nos referimos como encaminamiento tolerante a fallos basado en transiciones; TFTR) consiste en usar varias rutas disjuntas entre cada par de nodos origen-destino y seleccionar la ruta apropiada en el nodo fuente usando el mecanismo APM proporcionado por IBA. Consiste en migrar las rutas afectadas por el fallo a las rutas alternativas sin fallos. Sin embargo, con este fin, es necesario un algoritmo eficiente de encaminamiento capaz de proporcionar suficientesMontañana Aliaga, JM. (2008). Efficient mechanisms to provide fault tolerance in interconnection networks for pc clusters [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/2603Palanci

Synthesis of communicating decentralized supervisors for discrete-event systems with application to communication protocol synthesis

A Discrete-Event Systems (DES) may be viewed as a dynamic system with a discrete state space and a discrete state-transition structure with an event-driven nature, which makes it different from the systems described by differential or difference equations. Given the desired behavior of a DES as a specification, decentralized supervisory control theory seeks to design for a (distributed) DES, consisting of a number of (geographically distant) sites, a set of supervisors, one for each site, such that the behavior of the DES always remains within the specification. If the specification is not coobservable, these supervisors need to communicate amongst each other. This thesis proposes a mathematical framework to formally model and synthesize such communicating decentralized supervisors. The framework provides a decentralized representation of the DES's centralized supervisor and captures its observational and control-related information as mappings, which are called updating and guard functions, respectively. This leads to a polynomial dynamical system, which serves to model the required communication and synthesize its rules. The systematic synthesis, obtained through this approach, characterizes the class of distributed control problems which are solvable only with communication, comes up with a finer partition of it, and addresses practical issues. The thesis ends with the application of the theoretical results to the modeling and synthesis of a communication protoco

Efficient Passive Clustering and Gateways selection MANETs

Passive clustering does not employ control packets to collect topological information in ad hoc networks. In our proposal, we avoid making frequent changes in cluster architecture due to repeated election and re-election of cluster heads and gateways. Our primary objective has been to make Passive Clustering more practical by employing optimal number of gateways and reduce the number of rebroadcast packets