Application-driven Bandwidth Guarantees in Datacenters

Providing bandwidth guarantees to specific applications is be-coming increasingly important as applications compete for shared cloud network resources. We present CloudMirror, a solution that provides bandwidth guarantees to cloud applications based on a new network abstraction and workload placement algorithm. An effective network abstraction would enable applications to easily and accurately specify their requirements, while simultaneously enabling the infrastructure to provision resources efficiently for deployed applications. Prior research has approached the bandwidth guarantee specification by using abstractions that resemble physical network topologies. We present a contrasting approach of deriving a network abstraction based on application communication structure, called Tenant Application Graph or TAG. CloudMirror also incorporates a new workload place-ment algorithm that efficiently meets bandwidth requirements specified by TAGs while factoring in high availability consider-ations. Extensive simulations using real application traces and datacenter topologies show that CloudMirror can handle 40% more bandwidth demand than the state of the art (e.g., the Ok-topus system), while improving high availability from 20 % to 70%

CloudMirror: Application-Aware Bandwidth Reservations in the Cloud

Cloud computing providers today do not offer guarantees for the network bandwidth available in the cloud, preventing tenants from running their applications predictably. To provide guarantees, several recent research proposals offer tenants a virtual cluster abstraction, emulating physical networks. Whereas offering dedicated virtual network abstractions is a significant step in the right direction, in this paper we argue that the abstractions exposed to tenants should aim to model tenant application structures rather than aiming to mimic physical network topologies. The fundamental problem in providing users with dedicated network abstractions is that the communication patterns of real applications do not typically resemble the rigid physical network topologies. Thus, the virtual network abstractions often poorly represent the actual communication patterns, resulting in overprovisioned/wasted network resources and underutilized computational resources. We propose a new abstraction for specifying bandwidth guarantees, which is easy to use because it closely follows application models; our abstraction specifies guarantees as a graph between application components. We then propose an algorithm to efficiently deploy this abstraction on physical clusters. Through simulations, we show that our approach is significantly more efficient than prior work for offering bandwidth guarantees.

Tuning orbital-selective phase transitions in a two-dimensional Hund's correlated system

Hund's rule coupling ($\textit{J}$) has attracted much attention recently for its role in the description of the novel quantum phases of multi orbital materials. Depending on the orbital occupancy, $\textit{J}$ can lead to various intriguing phases. However, experimental confirmation of the orbital occupancy dependency has been difficult as controlling the orbital degrees of freedom normally accompanies chemical inhomogeneities. Here, we demonstrate a method to investigate the role of orbital occupancy in $\textit{J}$ related phenomena without inducing inhomogeneities. By growing SrRuO$_3$ monolayers on various substrates with symmetry-preserving interlayers, we gradually tune the crystal field splitting and thus the orbital degeneracy of the Ru \textit{t_2_g$}$ orbitals. It effectively varies the orbital occupancies of two-dimensional (2D) ruthenates. Via in-situ angle-resolved photoemission spectroscopy, we observe a progressive metal-insulator transition (MIT). It is found that the MIT occurs with orbital differentiation: concurrent opening of a band insulating gap in the $\textit{d$_x_y} band and a Mott gap in the \textit{d_x$$_z$$_/$$_y$$_z} bands. Our study provides an effective experimental method for investigation of orbital-selective phenomena in multi-orbital materials

CSpy: Finding the Best Quality Channel Without Probing,”

ABSTRACT Wireless performance depends directly on the quality of the channel. A wireless transmitter can improve its performance by estimating and transmitting on only the strongest channel, which can be of significantly higher quality than a weak channel (yielding up to 100% rate improvement). It is considered impossible to predict the quality of the unseen channels. Thus, the only way to identify the strongest channel is by probing each channel individually, incurring large overheads. The key contribution of this paper is a discovery of previously unobserved properties of the wireless channel that makes it possible to predict the the strongest of a set of channels from the measurements collected only on a single channel. We confirm the properties through measurements and present a theoretical analysis that explains their nature. Our proposed system, CSpy, utilizes these observations to predict the strongest channel. CSpy is the first to reliably estimate the strongest channel by utilizing channel responses extracted from off-the-shelf wireless chipsets, without probing any additional channels. By tracking the strongest channel, CSpy improves performance by up to 100% in comparison to channel agnostic schemes

Revamping the ieee 802.11a phy simulation models

In simulating wireless networks, modeling of the physical layer behavior is an important yet difficult task. Modeling and estimating wireless interference is receiving great research attention, and is crucial in a wireless network performance study. The implementation of physical layer capture, preamble detection, and carrier sense threshold plays an important role in successful frame reception in the presence of interference. We showed in our previous testbed study that the operations of the frame reception and the capture effect in real IEEE 802.11a systems differ from those of popular research simulators. We present our modifications of the IEEE 802.11a PHY models to the current simulators. The modifications can be summarized as follows. (i) The current simulators ’ frame reception is based only on the received signal strength. However, the real 802.11 systems can start the frame reception only when the Signal-to-Interference Ratio (SIR) is high enough to detect the preamble. (ii) Different chipset vendors implement the frame reception and capture algorithms differently, resulting in different operations for the same event. We provide different simulation models for several popular chipset vendors and show the performance differences between the models. (iii) The current simulators set the carrier sense threshold equal to the receiver sensitivity. The standard however states that it should be 20 dB higher than the receiver sensitivity. We implement our modifications to the QualNet simulator and conduct a wireless network performance study to evaluate the impact of PHY model implementation

BIVARIATE VERSION OF THE HAHN-SONINE THEOREM

Abstract. We consider orthogonal polynomials in two variables whose derivatives with respect to x are orthogonal. We show that they satisfy a system of partial differential equations of the form α(x, y) ∂ 2− → − → −→ x U n + β(x, y)∂x U n =ΛnUn, where deg α ≤ 2, deg β ≤ 1, − → U n = (Un0,Un−1,1, ·· ·,U0n) is a vector of polynomials in x and y for n ≥ 0, and Λn is an eigenvalue matrix of order (n +1) × (n +1) forn ≥ 0. Also we obtain several characterizations for these polynomials. Finally, we point out that our results are able to cover more examples than Bertran’s. 1