Cyclone Codes

We introduce Cyclone codes which are rateless erasure resilient codes. They combine Pair codes with Luby Transform (LT) codes by computing a code symbol from a random set of data symbols using bitwise XOR and cyclic shift operations. The number of data symbols is chosen according to the Robust Soliton distribution. XOR and cyclic shift operations establish a unitary commutative ring if data symbols have a length of $p-1$ bits, for some prime number $p$. We consider the graph given by code symbols combining two data symbols. If $n/2$ such random pairs are given for $n$ data symbols, then a giant component appears, which can be resolved in linear time. We can extend Cyclone codes to data symbols of arbitrary even length, provided the Goldbach conjecture holds. Applying results for this giant component, it follows that Cyclone codes have the same encoding and decoding time complexity as LT codes, while the overhead is upper-bounded by those of LT codes. Simulations indicate that Cyclone codes significantly decreases the overhead of extra coding symbols

Online scheduling in fault-prone systems: performance optimization and energy efficiency

Mención Internacional en el título de doctorEveryone is familiar with the problem of online scheduling (even if they are not aware of it), from the way we prioritize our everyday decisions to the way a delivery service must decide on the route to follow in order to cover the ongoing requests. In computer science, this is a problem of even greater importance. This thesis considers two main families of online scheduling problems in computer science, and aims to provide an extended clear framework for their analysis, presenting at the same time some common characteristics that connect these problems. The first and main family of online scheduling problems considered, is task scheduling in fault-prone computing systems. As the number of clients and the possibilities offered by the rapid development of computing systems, grow with time, the increase of demands of computationally intensive tasks is inevitable. Uniprocessors are no longer capable of coping with the escalation of these demands, which among others, has led to the development of multicore-based parallel machines, Internet-based computing platforms and co-operational distributed systems. Nonetheless, the challenges of these systems, even of the simplest ones, are numerous: They have to deal with continuous dynamic requests from the clients, which are probably not of the same nature (require different amount of computational resources). The processing elements (i.e., machines) may suffer from unpredictable failures, either malicious or due to overload. Furthermore, depending on the size of these systems and the exact processing units, their power consumption may be of significant amount; even equal to the electricity needed for a small town. Hence, limiting their power consumption is another challenge. To analyze such a system one must consider the online nature of the problem; the dynamic task arrivals (client requests) of different sizes (computational demands), and the unpredictable machine crashes and restarts (failures). It is important to give guarantees for the performance of the algorithms used in these systems, thus the thesis conducts worst-case competitive analysis and covers a significant level of the three dimensions of the problem. More precisely, it studies the effects of the number of machines, the number of different task sizes and the speed of the machines – which as will be explained through the thesis, affects the power consumption of the system – on the efficiency of online scheduling algorithms. As performance measures, this thesis uses the completed load, the pending load and the latency competitiveness of the algorithms. In some cases, it considers the long-term competitiveness versions of these measures as well. One of the most important results shown, is that resource augmentation in the form of increasing the machine speedup, is necessary in order to achieve some competitiveness, or to reach optimal competitiveness. The sufficient amount of speedup is found, and online algorithms that achieve the desired competitiveness are proposed and analyzed. Apart from the algorithms designed, some of the most widely used algorithms in scheduling are also analyzed in the model considered for the first time; namely, Longest In System (LIS), Shortest In System (SIS), Largest Processing Time (LPT), and Smallest Processing Time (SPT). Nonetheless, deciding on the best algorithm between them, is not easy. Each algorithm behaves better with respect to a different evaluation metric and under different model parameters. The second family of problems considered, is packet scheduling over an unreliable wireless communication link. As claimed, these problems have a strong connection to the task scheduling problem, especially when considering one machine and no speedup, hence some of the results can be shared. A setting with a single pair of nodes is considered, connected through an unreliable wireless channel. The sending station transmits packets to a receiving station over the channel, which can be jammed and hence corrupt the packet being transmitted. First, worst-case scenarios are assumed for the channel jams, modeled by a malicious adversarial entity. The packet arrivals however, follow a stochastic distribution and competitive analysis of scheduling algorithms is pursued giving matching bounds for the most pessimistic scenarios of channel jams. The aim of the algorithms is to find the schedule (or order or transmission of the arriving packets) in order to maximize the asymptotic throughout, which corresponds to the long-term competitive ratio of total length of successfully transmitted packets. Then, a slightly different problem is considered, assuming infinite amount of data to be transmitted over the same unreliable communication link. This time however, an adversarial entity with constrained power is assumed for the channel jams. The constrained power is modeled by an Adversarial Queueing Theory (AQT) approach, defined with two main parameters; "the error availability rate", and, the maximum batch of errors available to the adversary at any time. This is the first time AQT is used to model channel jams; it has been mostly used to model the packet arrivals in networking problems. In this problem, the scheduling algorithms must decide on the length of the packets to be transmitted, with the objective of maximizing the goodput rate; the rate of successfully transmitted load. It is seen, that even for the simplest settings, the analysis and results are not trivial.This work has been supported by IMDEA Networks InstitutePrograma Oficial de Doctorado en Ingeniería TelemáticaPresidente: María Serna Iglesias.- Secretario: Vincenzo Mancuso.- Vocal: Leszek Antoni Gasieni

Eighth International Symposium “Monitoring of Mediterranean Coastal Areas. Problems and Measurement Techniques”

The 8th International Symposium "Monitoring of Mediterranean Coastal Areas. Problems and Measurements Techniques" was organized by CNR-IBE in collaboration with FCS Foundation, and Natural History Museum of the Mediterranean and under the patronage of University of Florence, Accademia dei Geogofili, Tuscany Region and Livorno Province. It is the occasion in which scholars can illustrate and exchange their activities and innovative proposals, with common aims to promote actions to preserve coastal marine environment. Considering Symposium interdisciplinary nature, the Scientific Committee, underlining this holistic view of Nature, decided to celebrate Alexander von Humboldt; a nature scholar that proposed the organic and inorganic nature’s aspects as a single system. It represents a sign of continuity considering that in-presence Symposium could not be carried out due to the COVID-19 pandemic restrictions. Subjects are related to coastal topics: morphology; flora and fauna; energy production; management and integrated protection; geography and landscape, cultural heritage and environmental assets, legal and economic aspects

Distributed data structures and the power of topological self-stabilization

In dieser Arbeit betrachten wir Probleme im Bereich verteilter Systeme und lokaler Algorithmen. Wir betrachten verteilte Systeme, die gegeben sind durch bestimmte Topologien miteinander vernetzter Knoten, und stellen die Frage, ob solche Topologien wiederhergestellt werden können, wenn das Netzwerk durch den Ausfall oder Hinzukommen von Knoten oder Kanten verändert wird. Dabei sollen lokale verteilte Algorithmen entwickelt werden, die das Netzwerk von einer beliebigen schwach zusammenhängenden Starttopologie in eine Zieltopologie überführen. Diese Eigenschaft eines Algorithmus nennen wir topologische Selbststabilisierung. Motiviert wird diese Betrachtung durch die zunehmende Nutzung von Peer-to-Peer Systemen und von Cloud Dienstleistern, also Szenarien in denen das System aus Ressourcen besteht, für die Ausfälle nicht mehr kontrolliert werden können. Zur Analyse von topologisch selbststabilisierenden Algorithmen oder Protokollen führen wir geeignete Modelle ein. Wir präsentieren dann für einige bestimme Topologien mit welchen topologisch selbststabilisierenden Protokollen diese erreicht werden können. Wir betrachten dabei als einführendes Beispiel eine sortierte Liste von Knoten und fahren dann mit komplexeren Topologien wie einem Small-World Netzwerk und einem vollständigem Graphen fort. Als nächstes wenden wir die Idee von topologisch selbststabilisierenden Protokollen auf das Konzept von verteilten Hashtabellen an. Dabei zeigen wir, dass eine solche Lösung für bereits existierende verteilte Hashtabellen möglich ist und entwickeln dann eine weitere verteilte Hashtabelle, die heterogene Kapazitäten unterstützt. Zum Schluss betrachten wir, wie verteilte Hashtabellen erweitert werden können, sodass nicht nur exakte Suchanfragen sondern auch Suchanfragen nach ähnlichen Schlüsseln unterstützt werden.This thesis considers problems located in the fields of distributed systems and local algorithms. In particular we consider such systems given by specific topologies of interconnected nodes and want to examine whether these topologies can be rebuilt in case the network is (massively) changed by failing or joining nodes or edges. For this case we search for local distributed algorithms, i.e. the algorithms are executed on every single node and only use local information stored at the nodes like their neighborhood of nodes. By executing these algorithms we will show that the desired goal topologies can be reached from any weakly connected start topology. We call this property of an algorithm topological self-stabilization and motivate it by the increasing usage of peer-to-peer (P2P) systems and of cloud computing. In both cases the user or owner of the data and executed algorithms cannot control the resources and their connectivity. In order to analyze topological self-stabilizing algorithms or protocols we introduce suited models. For some specific topologies we then present and analyze topological self-stabilizing protocols. We consider topologies like a sorted list of nodes, which we use as a simple introductory example. We then proceed with more complex topologies like a specific small-world network and a clique. We then show that the concept of topological self-stabilization can be used for distributed hash tables. In particular we show that for existing distributed hash tables a topological self-stabilizing protocol canbe found. We also construct a new overlay network, that builds a distributed hash table that supports heterogeneous capacities, and a corresponding topological self-stabilizing protocol. At last we leave the concept of topological self-stabilization behind and instead show how to extend the usage of distributed hash tables, in order to answer more than only exact queries.Tag der Verteidigung: 21.05.2015Paderborn, Univ., Diss., 201

Proceedings of Eighth International Symposium “Monitoring of Mediterranean Coastal Areas. Problems and Measurement Techniques”

The 8th International Symposium "Monitoring of Mediterranean Coastal Areas. Problems and Measurements Techniques" was organized by CNR-IBE in collaboration with FCS Foundation, and Natural History Museum of the Mediterranean and under the patronage of University of Florence, Accademia dei Geogofili, Tuscany Region and Livorno Province. It is the occasion in which scholars can illustrate and exchange their activities and innovative proposals, with common aims to promote actions to preserve coastal marine environment. Considering Symposium interdisciplinary nature, the Scientific Committee, underlining this holistic view of Nature, decided to celebrate Alexander von Humboldt; a nature scholar that proposed the organic and inorganic nature’s aspects as a single system. It represents a sign of continuity considering that in-presence Symposium could not be carried out due to the COVID-19 pandemic restrictions. Subjects are related to coastal topics: morphology; flora and fauna; energy production; management and integrated protection; geography and landscape, cultural heritage and environmental assets, legal and economic aspects

Maritime expressions:a corpus based exploration of maritime metaphors

This study uses a purpose-built corpus to explore the linguistic legacy of Britain’s maritime history found in the form of hundreds of specialised ‘Maritime Expressions’ (MEs), such as TAKEN ABACK, ANCHOR and ALOOF, that permeate modern English. Selecting just those expressions commencing with ’A’, it analyses 61 MEs in detail and describes the processes by which these technical expressions, from a highly specialised occupational discourse community, have made their way into modern English. The Maritime Text Corpus (MTC) comprises 8.8 million words, encompassing a range of text types and registers, selected to provide a cross-section of ‘maritime’ writing. It is analysed using WordSmith analytical software (Scott, 2010), with the 100 million-word British National Corpus (BNC) as a reference corpus. Using the MTC, a list of keywords of specific salience within the maritime discourse has been compiled and, using frequency data, concordances and collocations, these MEs are described in detail and their use and form in the MTC and the BNC is compared. The study examines the transformation from ME to figurative use in the general discourse, in terms of form and metaphoricity. MEs are classified according to their metaphorical strength and their transference from maritime usage into new registers and domains such as those of business, politics, sports and reportage etc. A revised model of metaphoricity is developed and a new category of figurative expression, the ‘resonator’, is proposed. Additionally, developing the work of Lakov and Johnson, Kovesces and others on Conceptual Metaphor Theory (CMT), a number of Maritime Conceptual Metaphors are identified and their cultural significance is discussed