272 research outputs found
Scalable BGP Prefix Selection for Effective Inter-domain Traffic Engineering
Inter-domain Traffic Engineering for multi-homed networks faces a scalability
challenge, as the size of BGP routing table continue to grow. In this context,
the choice of the best path must be made potentially for each destination
prefix, requiring all available paths to be characterised (e.g., through
measurements) and compared with each other. Fortunately, it is well-known that
a few number of prefixes carry the larger part of the traffic. As a natural
consequence, to engineer large volume of traffic only few prefixes need to be
managed. Yet, traffic characteristics of a given prefix can greatly vary over
time, and little is known on the dynamism of traffic at this aggregation level,
including predicting the set of the most significant prefixes in the near
future. %based on past observations. Sophisticated prediction methods won't
scale in such context. In this paper, we study the relationship between prefix
volume, stability, and predictability, based on recent traffic traces from nine
different networks. Three simple and resource-efficient methods to select the
prefixes associated with the most important foreseeable traffic volume are then
proposed. Such proposed methods allow to select sets of prefixes with both
excellent representativeness (volume coverage) and stability in time, for which
the best routes are identified. The analysis carried out confirm the potential
benefits of a route decision engine
Dynamic Change Evaluation for Ontology Evolution in the Semantic Web
Changes in an ontology may have a disruptive impact on any system using it. This impact may depend on structural changes such as introduction or removal of concept definitions, or it may be related to a change in the expected performance of the reasoning tasks. As the number of systems using ontologies is expected to increase, and given the open nature of the Semantic Web, introduction of new ontologies and modifications to existing ones are to be expected. Dynamically handling such changes, without requiring human intervention, becomes crucial. This paper presents a framework that isolates groups of related axioms in an OWL ontology, so that a change in one or more axioms can be automatically localised to a part of the ontology
On the Breakdown of the Ehrenfest Method for Molecular Dynamics on Surfaces
Due to a continuum of electronic states present in periodic systems, the
description of molecular dynamics on surfaces poses a serious computational
challenge. One of the most used families of approaches in these settings are
friction theories, which are based on the Ehrenfest (EH) approach. Yet, a
mean-field treatment of electronic degrees of freedom in the EH method makes
this approach inaccurate in some cases. Our aim is to clarify when EH breaks
down for molecular dynamics on surfaces. Answering this question provides
limits of applicability for more approximate friction theories derived from EH.
We assess the EH method on one-dimensional, numerically exactly solvable models
with a large but finite number of electronic states. Using the Landau-Zener
formula and the Massey parameter, an expression that determines when EH breaks
down is deduced
Investigating Depth-Fanout Trade-Off in WiMAX Mesh Networks
peer reviewedIn the last years, Wireless Mesh Networks (WMNs) have been an emerging technology for providing cost/effective broadband Internet access. The research done insofar usually assumes that the wireless backbone of a WMN is built using IEEE 802.11 technologies. Such an approach has the drawback of leading to dense and sub-optimal deployments, due to the short transmission range of this standard. Recently standardized, the WiMAX technology is supposed to transcend this limitation by a transmission range of several miles. In particular, the mesh mode of the WiMAX standard enables direct communications between subscriber stations and, hence, reduces dead zones while increasing the global throughput. In this paper, we investigate the throughput capacity of a WiMAX mesh tree. More specifically, we are interested in balancing the impact of the depth of the tree with its fanout. We provide a traffic model and evaluate the WiMAX mesh tree by simulations
Let there be Chaining: How to Augment your IGP to Chain your Services
Ever since Network Functions Virtualization has replaced dedicated appliances, ISPs have been able to add a degree of flexibility in their traffic engineering. However, it also has increased the complexity of the optimization problem, because it is now necessary to place virtual functions and route traffic jointly. Insofar, a logically centralized approach has been taken, where a so-called orchestrator, having full knowledge of the network, the virtual functions, and the traffic, run complex algorithms to find a suitable solution to the problem. The outcome of the algorithms are then translated to network configurations to be pushed to all of the appliances. We argue that there is no need to fully centralize every decision, rather we can leverage existing network intelligence to achieve the same goal. In particular we propose to augment the routing layer with the notion of services, so to rely on the robustness and scalability of Interior Gateway Protocols (IGP). Our solution leverages on existing distributed routing protocols where, in addition, autonomous nodes announce information about the virtual services they provide. Our design is modular and incrementally deployable and has been implemented in what we call a NFV Router. In our evaluation, we show that (i) NFV Routers distributed chaining decisions are close to optimal centrally-computed paths, (ii) on a large scale testbed deployment, NFV Routers efficiently steer traffic through chains and only add a small overhead to control traffic and (iii) our distributed system, because of its local control loop, has a faster reaction to network events than centralized solutions
Populous: A tool for populating ontology templates
We present Populous, a tool for gathering content with which to populate an
ontology. Domain experts need to add content, that is often repetitive in its
form, but without having to tackle the underlying ontological representation.
Populous presents users with a table based form in which columns are
constrained to take values from particular ontologies; the user can select a
concept from an ontology via its meaningful label to give a value for a given
entity attribute. Populated tables are mapped to patterns that can then be used
to automatically generate the ontology's content. Populous's contribution is in
the knowledge gathering stage of ontology development. It separates knowledge
gathering from the conceptualisation and also separates the user from the
standard ontology authoring environments. As a result, Populous can allow
knowledge to be gathered in a straight-forward manner that can then be used to
do mass production of ontology content.Comment: in Adrian Paschke, Albert Burger begin_of_the_skype_highlighting
end_of_the_skype_highlighting, Andrea Splendiani, M. Scott Marshall, Paolo
Romano: Proceedings of the 3rd International Workshop on Semantic Web
Applications and Tools for the Life Sciences, Berlin,Germany, December 8-10,
201
Dynamic Packet Aggregation to Solve Performance Anomaly in 802.11 Wireless Networks
In the widely used 802.11 standard, the so called performance anomaly is a
well known issue. Several works have tried to solve this problem by introducing
mechanisms such as packet fragmentation, backoff adaptation, or packet
aggregation during a fixed time interval. In this paper, we propose a novel
approach solving the performance anomaly problem by packet aggregation using a
dynamic time interval, which depends on the busy time of the wireless medium.
Our solution differs from other proposition in the literature because of this
dynamic time interval, which allows increasing fairness, reactivity, and in
some cases efficiency. In this article, we emphasize the performance evaluation
of our proposal
Performance Benchmarking of State-of-the-Art Software Switches for NFV
With the ultimate goal of replacing proprietary hardware appliances with
Virtual Network Functions (VNFs) implemented in software, Network Function
Virtualization (NFV) has been gaining popularity in the past few years.
Software switches route traffic between VNFs and physical Network Interface
Cards (NICs). It is of paramount importance to compare the performance of
different switch designs and architectures. In this paper, we propose a
methodology to compare fairly and comprehensively the performance of software
switches. We first explore the design spaces of seven state-of-the-art software
switches and then compare their performance under four representative test
scenarios. Each scenario corresponds to a specific case of routing NFV traffic
between NICs and/or VNFs. In our experiments, we evaluate the throughput and
latency between VNFs in two of the most popular virtualization environments,
namely virtual machines (VMs) and containers. Our experimental results show
that no single software switch prevails in all scenarios. It is, therefore,
crucial to choose the most suitable solution for the given use case. At the
same time, the presented results and analysis provide a deeper insight into the
design tradeoffs and identifies potential performance bottlenecks that could
inspire new designs.Comment: 17 page
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