17,564 research outputs found
The Internet's unexploited path diversity
The connectivity of the Internet at the Autonomous System level is influenced
by the network operator policies implemented. These in turn impose a direction
to the announcement of address advertisements and, consequently, to the paths
that can be used to reach back such destinations. We propose to use directed
graphs to properly represent how destinations propagate through the Internet
and the number of arc-disjoint paths to quantify this network's path diversity.
Moreover, in order to understand the effects that policies have on the
connectivity of the Internet, numerical analyses of the resulting directed
graphs were conducted. Results demonstrate that, even after policies have been
applied, there is still path diversity which the Border Gateway Protocol cannot
currently exploit.Comment: Submitted to IEEE Communications Letter
Exploring networks with traceroute-like probes: theory and simulations
Mapping the Internet generally consists in sampling the network from a
limited set of sources by using traceroute-like probes. This methodology, akin
to the merging of different spanning trees to a set of destination, has been
argued to introduce uncontrolled sampling biases that might produce statistical
properties of the sampled graph which sharply differ from the original ones. In
this paper we explore these biases and provide a statistical analysis of their
origin. We derive an analytical approximation for the probability of edge and
vertex detection that exploits the role of the number of sources and targets
and allows us to relate the global topological properties of the underlying
network with the statistical accuracy of the sampled graph. In particular, we
find that the edge and vertex detection probability depends on the betweenness
centrality of each element. This allows us to show that shortest path routed
sampling provides a better characterization of underlying graphs with broad
distributions of connectivity. We complement the analytical discussion with a
throughout numerical investigation of simulated mapping strategies in network
models with different topologies. We show that sampled graphs provide a fair
qualitative characterization of the statistical properties of the original
networks in a fair range of different strategies and exploration parameters.
Moreover, we characterize the level of redundancy and completeness of the
exploration process as a function of the topological properties of the network.
Finally, we study numerically how the fraction of vertices and edges discovered
in the sampled graph depends on the particular deployements of probing sources.
The results might hint the steps toward more efficient mapping strategies.Comment: This paper is related to cond-mat/0406404, with explorations of
different networks and complementary discussion
Characterising Web Site Link Structure
The topological structures of the Internet and the Web have received
considerable attention. However, there has been little research on the
topological properties of individual web sites. In this paper, we consider
whether web sites (as opposed to the entire Web) exhibit structural
similarities. To do so, we exhaustively crawled 18 web sites as diverse as
governmental departments, commercial companies and university departments in
different countries. These web sites consisted of as little as a few thousand
pages to millions of pages. Statistical analysis of these 18 sites revealed
that the internal link structure of the web sites are significantly different
when measured with first and second-order topological properties, i.e.
properties based on the connectivity of an individual or a pairs of nodes.
However, examination of a third-order topological property that consider the
connectivity between three nodes that form a triangle, revealed a strong
correspondence across web sites, suggestive of an invariant. Comparison with
the Web, the AS Internet, and a citation network, showed that this third-order
property is not shared across other types of networks. Nor is the property
exhibited in generative network models such as that of Barabasi and Albert.Comment: To appear at IEEE/WSE0
Multi Agent Systems in Logistics: A Literature and State-of-the-art Review
Based on a literature survey, we aim to answer our main question: ĂąâŹĆHow should we plan and execute logistics in supply chains that aim to meet todayĂąâŹâąs requirements, and how can we support such planning and execution using IT?ù⏠TodayĂąâŹâąs requirements in supply chains include inter-organizational collaboration and more responsive and tailored supply to meet specific demand. Enterprise systems fall short in meeting these requirements The focus of planning and execution systems should move towards an inter-enterprise and event-driven mode. Inter-organizational systems may support planning going from supporting information exchange and henceforth enable synchronized planning within the organizations towards the capability to do network planning based on available information throughout the network. We provide a framework for planning systems, constituting a rich landscape of possible configurations, where the centralized and fully decentralized approaches are two extremes. We define and discuss agent based systems and in particular multi agent systems (MAS). We emphasize the issue of the role of MAS coordination architectures, and then explain that transportation is, next to production, an important domain in which MAS can and actually are applied. However, implementation is not widespread and some implementation issues are explored. In this manner, we conclude that planning problems in transportation have characteristics that comply with the specific capabilities of agent systems. In particular, these systems are capable to deal with inter-organizational and event-driven planning settings, hence meeting todayĂąâŹâąs requirements in supply chain planning and execution.supply chain;MAS;multi agent systems
- âŠ