Skew

About: Skew is a research topic. Over the lifetime, 8792 publications have been published within this topic receiving 98985 citations.

Estimation and removal of clock skew from network delay measurements

Abstract: Packet delay and loss traces are frequently used by network engineers, as well as network applications, to analyze network performance. The clocks on the end-systems used to measure the delays, however, are not always synchronized, and this lack of synchronization reduces the accuracy of these measurements. Therefore, estimating and removing relative skews and offsets from delay measurements between sender and receiver clocks are critical to the accurate assessment and analysis of network performance. We introduce a linear programming-based algorithm to estimate the clock skew in network delay measurements and compare it with three other algorithms. We show that our algorithm has a time complexity of O(N), leaves the delay after the skew removal positive, and is robust in the sense that the error margin of the skew estimate is independent of the magnitude of the skew. We use traces of real Internet delay measurements to assess the algorithm, and compare its performance to that of three other algorithms. Furthermore, we show through simulation that our algorithm is unbiased, and that the sample variance of the skew estimate is better (smaller) than existing algorithms.

SkewTune: mitigating skew in mapreduce applications

Abstract: We present an automatic skew mitigation approach for user-defined MapReduce programs and present SkewTune, a system that implements this approach as a drop-in replacement for an existing MapReduce implementation. There are three key challenges: (a) require no extra input from the user yet work for all MapReduce applications, (b) be completely transparent, and (c) impose minimal overhead if there is no skew. The SkewTune approach addresses these challenges and works as follows: When a node in the cluster becomes idle, SkewTune identifies the task with the greatest expected remaining processing time. The unprocessed input data of this straggling task is then proactively repartitioned in a way that fully utilizes the nodes in the cluster and preserves the ordering of the input data so that the original output can be reconstructed by concatenation. We implement SkewTune as an extension to Hadoop and evaluate its effectiveness using several real applications. The results show that SkewTune can significantly reduce job runtime in the presence of skew and adds little to no overhead in the absence of skew.

Models of reproductive skew: A review and synthesis (Invited Article)

Abstract: Animal societies vary markedly in reproductive skew, the extent to which breeding is monopolised by dominant individuals. In the last few years, a large number of different models have been developed to explain this variation. Here, I review existing models of reproductive skew, distinguishing between two basic types. Transactional models focus on group stability and the constraints this places on the division of reproduction. Compromise models, by contrast, ignore issues of group stability and view the division of reproduction as the outcome of a conflict in which each group member has a limited or partial ability to enforce its own optimum. I go on to show, however, that the division between transactional and compromise models is somewhat artificial, and that both approaches may be combined in a single, synthetic treatment. Different models of reproductive skew are thus better seen as special cases of a general underlying theory, rather than alternative paradigms. I conclude with a brief discussion of the possibilities and problems of empirically testing this unified theory of skew, and the prospects for future theoretical advances.

High Speed Signal Propagation: Advanced Black Magic

Abstract: Raves for Dr. Johnson's previous classic, High-Speed Digital Design!In High-Speed Signal Propagation, Howard Johnson and Martin Graham bring together state-of-the-art techniques for building digital interconnections that can transmit faster, farther, and more efficiently than ever before. Packed with new examples and never-before-published high-speed design guidance, this book offers a complete and unified theory of signal propagation for all metallic media, from cables to pcb traces to chips. Coverage includes: Managing tradeoffs between speed and distance Physical theory of signal impairments: skin and proximity effects, dielectric loss, surface roughness, and non-TEM mode propagation Generalized frequency- and step-response models Calculation of time-domain waveforms from frequency-domain transfer functions Differential signaling: Edge-coupled and broadside-coupled differential pairs, bends, intra-pair skew, differential trace geometry impedance, crosstalk, and radiation Inter-cabinet connections: Coax, twisted-pair, fiber, equalizers, and LAN building wiring Clock distribution: Special requirements, repeaters, multi-drop clock distribution, jitter, and power filtering Simulation: Frequency domain simulation methods, Spice, and IBIS

International Asset Allocation Under Regime Switching, Skew and Kurtosis Preferences

Abstract: This paper proposes a new tractable approach to solving asset allocation problems in situations with a large number of risky assets which pose problems for standard approaches. Investor preferences are assumed to be defined over moments of the wealth distribution such as its mean, variance, skew and kurtosis. Time-variations in investment opportunities are represented by a flexible regime switching process. We develop analytical methods that only require solving a small set of difference equations and can be applied even in the presence of large numbers of risky assets. In the context of a four-moment international CAPM specification that relates stock returns in five regions to returns on a global market portfolio, we find evidence of distinct bull and bear states. Ignoring regimes, an unhedged US investor's optimal portfolio is strongly diversified internationally. The presence of regimes in the return distribution leads to a large increase in the investor's optimal holdings of US stocks as does the introduction of skew and kurtosis preferences. Our paper therefore offers an explanation of the strong home bias observed in US investors' asset allocation based on regime switching and skew and kurtosis preferences.