32 research outputs found
Policies for Self Tuning Home Networks
No full textA home network (HN) is usually managed by a user who does not possess knowledge and skills required to perform management tasks. When abnormalities are detected, it is desirable to let the network tune itself under the direction of certain policies. However, self tuning tasks usually require coordination between several network components and most of the network management policies can only specify local tasks. In this paper, we propose a state machine based policy framework to address the problem of fault and performance management in the context of HN. Policies can be specified for complex management tasks as global state machines which incorporate global system behaviour monitoring and reactions. We demonstrate the policy framework through a case study in which policies are specified for dynamic selection of frequency channel in order to improve wireless link quality in the presence of RF interference
HomeShaper: regulating the use of bandwidth resources in home networks
No full textIt is estimated that the number of worldwide broadband Internet subscribers increases at a staggering rate of 8% per year. This fact, along with the ever increasing data consumption demands, have pushed the envelope in the design of faster and better broadband Internet and wireless LAN communications. Nonetheless, home users still experience periods during which the available network resources do not suffice to meet everyone’s requirements, confirming Parkinson’s law of bandwidth absorption: “network traffic expands to fi the available bandwidth”.
Unsurprisingly, numerous sociological studies indicate that a highly desired manage- ment functionality is: “the ability of users to effectively regulate the use of a home network’s bandwidth resources”. Past research on this topic usually proposes over- complicated solutions that are specific to certain technologies and not tailored to the unique characteristics of home networks. First, the average home user does not possess the skills to efficiently manage his/her own network. Second, home networking equipment offer limited management functionalities via heterogeneous user interfaces. Finally, home networks exhibit highly dynamic performance characteristics, affecting the amount of available bandwidth resources over time and space.
This thesis presents HomeShaper , a programmable bandwidth management frame- work which accepts as input a set of user-defi requirements in the form of high-level contracts (e.g. guaranteed rate, capping, prioritisation etc.), and transparently reconfigures the underlying home network infrastructure in order to fulfil them. HomeShaper provides strong guarantees about the correctness of the resulting network configurations, preventing inconsistencies by means of verification. Furthermore it allows the specification of adaptive bandwidth control behaviours, used to dynamically enable or disable individual contracts, responding to the changing network performance conditions. The developers of home network management applications can easily specify custom adaptive behaviours encoded in the form of “teleo-reactive” programs, and rely on the tools and the abstractions provided by HomeShaper runtimeOpen Acces
Faithful reproduction of network experiments
No full textThe proliferation of cloud computing has compelled the research community to rethink fundamental design aspects of networked systems. However, the tools commonly used to evaluate new ideas have not kept abreast of the latest developments. Common simulation and emulation frameworks fail to provide scalability, fidelity, reproducibility and execute unmodified code, all at the same time. We present SELENA, a Xen-based network emulation framework that offers fully reproducible experiments via its automation interface and supports the use of unmodified guest operating systems. This allows out-of-the-box compatibility with common applications and OS components, such as network stacks and filesystems. In order to faithfully emulate faster and larger networks, SELENA adopts the technique of time dilation and transparently slows down the passage of time for guest operating systems. This technique effectively virtualizes the availability of host's hardware resources and allows the replication of scenarios with increased I/O and computational demands. Users can directly control the trade-off between fidelity and running-times via intuitive tuning knobs. We evaluate the ability of SELENA to faithfully replicate the behavior of real systems and compare it against existing popular experimentation platforms. Our results suggest that SELENA can ac-curately model networks with aggregate link speeds of 44 Gbps or more, while improving by four times the execution time in comparison to ns3 and exhibits near-linear scaling properties
Performance and scalability evaluation of the Castalia wireless sensor network simulator
No full textFrom simulation to real deployments in WSN and back
No full textThe paper presents our efforts to validate some high-level aspects of the WSN simulator we have built as well as the operational functionality of our multiparameter MAC protocol. In order to do so, we resort to real deployments involving TelosB motes. The simulator, named Castalia, boasts the most accurate wireless channel and radio models for WSN found in current literature. These models are capturing some essential experimental findings. This does not guaranty though that the simulator will behave similarly with a real deployment at the high level (i.e., the protocol or application level). We investigate how our multiparameter MAC protocol behaves in a real deployment so as to take a first step towards validating and possibly tuning Castalia. The investigation starts by determining the connectivity map for the real deployment and then trying to reproduce it in the simulator. We then proceed with the protocol testing and comparing. We report the difficulties faced and our findings from this process. 1
From rural to urban settings: life on the margins in the short stories of Dimosthenis Voutiras
No full textThis thesis has been focused on the research of the literary characters in the short stories of Dimosthenis Voutiras, one of the pioneer literary writers of his generation. More specifically, the explanatory interest turned to the characters which have been socially marginalised. These characters are depicted in short stories that cover a chronological period from the beginning of the author’s writing presence and ends at the middle of the Interwar Era. This thesis has been developed methodologically by utilising textual and extratextual criteria, making use of hermeneutic tools from narratology as well as from the scientific field of sociology. More precisely, the theoretical compass of the thesis was a narrative approach which is based on the wider theoretical framework of Gerard Genette, but also the typology of Dorrit Cohn about a research regarding the conscience of the fictional characters throughout a more stylistic type of analysis. In addition to this, vital findings regarding the depiction of the characters were emerged from the use of Mikhail Bakhtin's theory about dialogism and his conclusions concerning elements of Carnival. Furthermore, the approach to the behaviour and the identity of the socially marginalised characters, as they are attributed by the author, was achieved through cultural studies, and more particularly through the theoretical studies of Pierre Bourdieu regarding the life models of the popular (lower) class. As far as the categorisation of the characters is concerned, the typology which was used throughout the thesis was mainly that of Shlomith Rimmon – Kenan. The conclusions regarding the attribution of the social imprint and the political and philosophical ideas of the characters, place those characters into the spectrum of verisimilitude. Η παρούσα διατριβή επικεντρώθηκε στη μελέτη των λογοτεχνικών χαρακτήρων στα διηγήματα του Δημοσθένη Βουτυρά. Πιο συγκεκριμένα, το ερμηνευτικό ενδιαφέρον στράφηκε στους χαρακτήρες του κοινωνικού περιθωρίου, όπως αυτοί αποτυπώνονται σε διηγήματα που καλύπτουν χρονικά μια περίοδο από την αρχή της συγγραφικής παρουσίας του λογοτέχνη ως τα μέσα της μεσοπολεμικής περιόδου. Μεθοδολογικά η διατριβή αναπτύχθηκε αξιοποιώντας κειμενικά και εξωκειμενικά κριτήρια, με ερμηνευτικά εργαλεία από την αφηγηματολογία αλλά και το επιστημονικό πεδίο της κοινωνιολογίας. Πιο ειδικά, θεωρητικές πυξίδες αποτέλεσαν, η αφηγηματολογική προσέγγιση βάσει του ευρύτερου θεωρητικού σχήματος του Gerard Genette και η τυπολογία της Dorrit Cohn για τη μελέτη της συνείδησης των μυθοπλαστικών προσώπων σε μια πιο υφολογικού τύπου ανάλυση, ενώ σημαντικά ευρήματα για την αποτύπωση των χαρακτήρων αναδύθηκαν από την αξιοποίηση της θεωρίας του Bakhtin για τη διαλογικότητα και των συμπερασμάτων του σχετικά με το καρναβαλικό στοιχείο. Επιπλέον, η προσέγγιση της συμπεριφοράς και της ταυτότητας των περιθωριακών χαρακτήρων όπως τους αποδίδει ο συγγραφέας έγινε μέσω των πολιτισμικών σπουδών και ειδικότερα των θεωρητικών μελετών του Pierre Bourdieu, αναφορικά με τα μοντέλα ζωής της λαϊκής τάξης. Για την κατηγοριοποίηση των χαρακτήρων χρησιμοποιήθηκε κυρίως το μοντέλο της Shlomith Rimmon – Kenan. Τα συμπεράσματα σχετικά με την απόδοση του κοινωνικού αποτυπώματος, των πολιτικών και φιλοσοφικών ιδεών, τοποθετούν τους χαρακτήρες του Βουτυρά στο φάσμα της ρεαλιστικής αφήγησης.
Resolving data center power bill disputes: the energy-performance trade-offs of consolidation
No full textIn this paper we challenge the common evaluation practices used for Virtual Machine (VM) consolidation, such as simulation and small testbeds, which fail to capture the fundamental trade-off between energy consumption and performance. We identify a number of over-simplifying assumptions which are typically made about the energy consumption and performance characteristics of modern networked systems. In response, we describe how more accurate models for data-center systems can be designed and used in order to create an evaluation framework that allows the more reliable exploration of the energy-performance trade-off for VM consolidation strategies
Home Network Management Policies: Putting the User in the Loop.
No full text30.01.13 KB Accepted version ok to add to Spiral. IEEEHome networks are becoming increasingly complex but existing management solutions are not simple to use since they are not tailored to the needs of typical home-users. In this paper we present a new approach to home network management that allows users to formulate quite sophisticated comic-strip policies using an attractive iPad application. The policies are based on the management wishes of home users elicited in a user study. Comic-strip policies are passed to a Policy engine running on a new Home Network Router designed to facilitate a variety of management tasks. We illustrate our approach via a number end-to-end experiments in an actual home deployment, using our prototype implementation. © 2012 IEEE
Environmental contestation in China: Motives and impact
No full textEnvironmental legislation in China prescribes Public Participation in Environmental Impact Assessment to be arranged by the initiator of a project. Nevertheless concerns of effected citizens are often neglected and not addressed in the impact studies. The rising public environmental awareness and realization of health risks related to the proposed activity can lead to outbreaks of public protests and mass events, which may result in cancellation of such projects. In this paper some recent cases of contestation in China are presented and their impact on environmental decision-making analysed. It shows that the Chinese public does have an impact on policy making and stimulates the government to sharpen environmental regulation and procedures.Policy Analysi
Ion current sensing for controlled auto ignition in internal combustion engines
No full textEnvirom-nental pollution is a subject that needs urgent addressing. Since the internal combustion engine has its fair share of accountability on this, research on techniques for increasing engine efficiency and emissions is necessary. Controlled Auto Ignition is a promising combustion mode, which increases fuel efficiency while also reducing NOx emissions to negligible levels. This Thesis concentrates on the implementation of this mode through experimental research, on an engine equipped with a fully variable valvetrain. Investigation of the operational window, emissions, fuel consumption, thermodynamic efficiency is carried out and ways to improve on these are discussed. The governing consideration, however, is the control method for this rather intricate combustion mode. As such, experimental data acquisition and analysis of ion current under the whole operating spectrum, from spark ignition to full autoignition is made. It is found that the expected gains in fuel consumption and emissions are realized. In addition, ion current proves to be a very powerful and cost effective tool for engine monitoring, diagnosis and control. The author concludes that Controlled Auto Ignition is a viable proposition for mass production engine designs and that ion current, although not absolutely vital for engine control, considerably increases engine control thus allowing for greater operating window under autoignition, without compromising reliability or cost.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
