Alcatel-Lucent

About: Alcatel-Lucent is a based out in Stuttgart, Germany. It is known for research contribution in the topics: Signal & Network packet. The organization has 37003 authors who have published 53332 publications receiving 1430547 citations. The organization is also known as: Alcatel-Lucent S.A. & Alcatel.

Model Checking Partial State Spaces with 3-Valued Temporal Logics

Abstract: We address the problem of relating the result of model checking a partial state space of a system to the properties actually possessed by the system. We represent incomplete state spaces as partial Kripke structures, and give a 3-valued interpretation to modal logic formulas on these structures. The third truth value ⊥ means "unknown whether true or false". We define a preorder on partial Kripke structures that reflects their degree of completeness. We then provide a logical characterization of this preorder. This characterization thus relates properties of less complete structures to properties of more complete structures. We present similar results for labeled transition systems and show a connection to intuitionistic modal logic. We also present a 3-valued CTL model checking algorithm, which returns ⊥ only when the partial state space lacks information needed for a definite answer about the complete state space.

The importance of long-range dependence of VBR video traffic in ATM traffic engineering: myths and realities

Abstract: There has been a growing concern about the potential impact of long-term correlations (second-order statistic) in variable-bit-rate (VBR) video traffic on ATM buffer dimensioning. Previous studies have shown that video traffic exhibits long-range dependence (LRD) (Hurst parameter large than 0.5). We investigate the practical implications of LRD in the context of realistic ATM traffic engineering by studying ATM multiplexers of VBR video sources over a range of desirable cell loss rates and buffer sizes (maximum delays). Using results based on large deviations theory, we introduce the notion of Critical Time Scale (CTS). For a given buffer size, link capacity, and the marginal distribution of frame size, the CTS of a VBR video source is defined as the number of frame correlations that contribute to the cell loss rate. In other words, second-order behavior at the time scale beyond the CTS does not significantly affect the network performance. We show that whether the video source model is Markov or has LRD, its CTS is finite, attains a small value for small buffer, and is a non-decreasing function of buffer size. Numerical results show that (i) even in the presence of LRD, long-term correlations do not have significant impact on the cell loss rate; and (ii) short-term correlations have dominant effect on cell loss rate, and therefore, well-designed Markov traffic models are effective for predicting Quality of Service (QOS) of LRD VBR video traffic. Therefore, we conclude that it is unnecessary to capture the long-term correlations of a real-time VBR video source under realistic ATM buffer dimensioning scenarios as far as the cell loss rates and maximum buffer delays are concerned.

Routing and wavelength assignment of scheduled lightpath demands

Abstract: We present algorithms that compute the routing and wavelength assignment (RWA) for scheduled lightpath demands in a wavelength-switching mesh network without wavelength conversion functionality. Scheduled lightpath demands are connection demands for which the setup and teardown times are known in advance. We formulate separately the routing problem and the wavelength assignment problem as spatio-temporal combinatorial optimization problems. For the former, we propose a branch and bound algorithm for exact resolution and an alternative tabu search algorithm for approximate resolution. A generalized graph coloring approach is used to solve the wavelength assignment problem. We compared the proposed algorithms to an RWA algorithm that sequentially computes the route and wavelength assignment for the scheduled lightpath demands.

Selectivity estimation in spatial databases

Abstract: Selectivity estimation of queries is an important and well-studied problem in relational database systems. In this paper, we examine selectivity estimation in the context of Geographic Information Systems, which manage spatial data such as points, lines, poly-lines and polygons. In particular, we focus on point and range queries over two-dimensional rectangular data. We propose several techniques based on using spatial indices, histograms, binary space partitionings (BSPs), and the novel notion of spatial skew. Our techniques carefully partition the input rectangles into subsets and approximate each partition accurately. We present a detailed experimental study comparing the proposed techniques and the best known sampling and parametric techniques. We evaluate them using synthetic as well as real-life TIGER datasets. Based on our experiments, we identify a BSP based partitioning that we call Min-Skew which consistently provides the most accurate selectivity estimates for spatial queries. The Min-Skew partitioning can be constructed efficiently, occupies very little space, and provides accurate selectivity estimates over a broad range of spatial queries.

Phonon density of states and negative thermal expansion in ZrW2O8

Abstract: Thermal expansion of solids arises from anharmonic lattice dynamics. The contrasting phenomenon of negative thermal expansion (NTE)—where expansion occurs on cooling rather than heating—was discovered1 in ZrW2O8 in 1968. Recently, this material has attracted interest in the context of NTE for several reasons: the magnitude of the effect is relatively large (−9 p.p.m. K−1); the temperature range over which NTE occurs is also large (from close to absolute zero up to the decomposition temperature of about 1,050 K); and the NTE effect is isotropic2, evidenced by the fact that ZrW2O8 remains cubic at all temperatures. These characteristics make ZrW2O8 an important system in which to study unusual lattice dynamics of this type, and potentially well suited for application in composite materials with an engineered thermal expansion coefficient3. Here we report neutron-scattering measurements of ZrW2O8 that allow us to investigate its phonon spectrum, and hence determine the energy scale for the lattice motions governing NTE. We find that NTE can be modelled by several low-energy phonon modes, suggesting that the effect arises from the unusual crystal structure of ZrW2O8, which supports highly anharmonic vibrational modes.