bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTRON SPIN RESONANCE AS A PROBE OF COLLECTIVE MODES IN ANISOTROPIC EXCHANGE-COUPLED PARAMAGNETS
Authors: HUBER D. L.
Published: September 2012

Electron spin resonance (ESR) in exchanged-coupled paramagnets is a probe of field-dependent collective modes in a strongly coupled many-body system. We utilize a previously developed approach for the analysis of collective modes in such systems to express the experimentally determined g-factors of the ESR modes in an anisotropic magnet in terms of the microscopic (isolated spin) g-factors and the ratios of the static susceptibilities along the principal directions. Applications of the theory to the ferromagnetic insulator CrBr 3 and the Kondo lattice systems YbRh 2 Si 2, YbCo 2 Si 2, YbIr 2 Si 2 and CeRuPO are discussed.
GEODESIC STRUCTURE OF TEST PARTICLE IN BARDEEN SPACETIME
Authors: ZHOU SHENG , CHEN JUHUA , WANG YONGJIU
Published: September 2012

The Bardeen model describes a regular spacetime, i.e. a singularity-free black hole spacetime. In this paper, by analyzing the behavior of the effective potential for the particles and photons, we investigate the timelike and null geodesic structures in the Bardeen spacetime. At the same time, all kinds of orbits, which are allowed according to the energy level corresponding to the effective potentials, are numerically simulated in detail. We find many-world bound orbits, two-world escape orbits and escape orbits in this spacetime. We also find that bound orbits precession directions are opposite and their precession velocities are different, the inner bound orbits shift along counter-clockwise with high velocity while the exterior bound orbits shift along clockwise with low velocity.
NUMERICAL HEDGING OF ELECTRICITY CONTRACTS USING DIMENSION REDUCTION
Authors: HEPPERGER PETER
Published: September 2012

The basic contracts traded on energy exchanges involve fixed-rate payments for the delivery of electricity over a certain period of time. It has been shown that options on these electricity swaps can be priced efficiently using a Hilbert space-valued time-inhomogeneous jump-diffusion model for the forward curve. We consider the mean-variance hedging problem for European options under this model. The computation of hedging strategies leads to quadratic optimization problems whose parameters depend on the solution of an infinite-dimensional partial integro-differential equation. The main objective of this article is to find an efficient numerical algorithm for this task. Using proper orthogonal decomposition (a dimension reduction method), approximately optimal strategies are computed. We prove convergence of the corresponding hedging error to the minimal achievable error in the electricity market. Numerical experiments are performed to analyze the resulting hedging strategies.
TENOR SPECIFIC PRICING
Authors: MADAN DILIP B. , SCHOUTENS WIM
Published: September 2012

Observing that pure discount projection curves are now based on a variety of tenors leads us to enquire into the possibility of theoretically deriving tenor specific zero coupon bond prices. The question then also arises on how to construct tenor specific prices for all financial contracts. Noting that in conic finance one has the law of two prices, bid and ask, that are nonlinear functions of the random variables being priced, we model dynamically consistent sequences of such prices using the theory of nonlinear expectations. The latter theory is closely connected to solutions of backward stochastic difference equations. The drivers for these stochastic difference equations are here constructed using concave distortions that implement risk charges for local tenor specific risks. It is then observed that tenor specific prices given by the mid quotes of bid and ask converge to the risk neutral price as the tenor is decreased and liquidity increased when risk charges are scaled by the tenor. Square root tenor scaling can halt the convergence to risk neutral pricing, preserving bid ask spreads in the limit. The greater liquidity of lower tenors may lead to an increase or decrease in prices depending on whether the lower liquidity of a higher tenor has a mid quote above or below the risk neutral value. Generally for contracts with a large upside and a bounded downside the prices fall with liquidity while the opposite is the case for contracts subject to a large downside and a bounded upside.
A GENERAL COMPUTATION SCHEME FOR A HIGH-ORDER ASYMPTOTIC EXPANSION METHOD
Authors: TAKAHASHI AKIHIKO , TAKEHARA KOHTA , TODA MASASHI
Published: September 2012

This paper presents a new computational scheme for an asymptotic expansion method of an arbitrary order. The asymptotic expansion method in finance initiated by Kunitomo and Takahashi (1992), Yoshida (1992b) and Takahashi (1995, 1999) is a widely applicable methodology for an analytic approximation of expectation of a certain functional of diffusion processes. Hence, not only academic researchers but also many practitioners have used the methodology for a variety of financial issues such as pricing or hedging complex derivatives under high-dimensional underlying stochastic environments. In practical applications of the expansion, a crucial step is calculation of conditional expectations for a certain kind of Wiener functionals. Takahashi (1995, 1999) and Takahashi and Takehara (2007) provided explicit formulas for those conditional expectations necessary for the asymptotic expansion up to the third order. This paper presents the new method for computing an arbitrary-order expansion in a general diffusion-type stochastic environment, which is powerful especially for high-order expansions: We develops a new calculation algorithm for computing coefficients of the expansion through solving a system of ordinary differential equations that is equivalent to computing the conditional expectations directly. To demonstrate its effectiveness, the paper gives numerical examples of the approximation for a λ-SABR model up to the fifth order.
The Rationale for IPO Lockup Agreements: Agency or Signaling?
Authors: Gao Fei , Siddiqi Mazhar A.
Published: September 2012

Most Initial Public Offerings (IPOs) feature share lockup agreements, which prohibit insiders and other pre-IPO shareholders from selling their shares for a specified period of time following IPO. We explore possible reasons why some IPO firms voluntarily agree to have a much longer lockup period than other firms. We find evidence that lockup agreements are used to control agency costs. Longer lockups are significantly related to inferior long-run returns and this relationship is stronger for firms that have less reputable underwriters. We find no evidence that lockup agreements are used to signal firm quality and we are unable to relate firm quality, as measured by long-run returns, to information asymmetry variables.
DENSITY FUNCTIONAL THEORY STUDIES OF SPECTROSCOPIC CONSTANTS AND ANHARMONIC FORCE FIELD OF O35ClO
Authors: ZHU ZILIANG , WANG MEISHAN , YANG CHUANLU , MA MEIZHONG , LIU WENWANG
Published: September 2012

The equilibrium structure, spectroscopy constants and anharmonic force field of O35ClO have been calculated at B3PW91 and B3LYP levels of theory with two basis sets 6-311++G(2df,2pd) and 6-311++G(3df,3pd) , respectively. The computed geometries, dipole moment, rotational constants, vibration–rotation interaction constants, vibrational band origins, anharmonic constants, quartic, and sextic centrifugal distortion constants are compared with the available experimental data. The cubic and quartic force constants are predicted. The calculated results show that the B3PW91 results are in excellent agreement with experiment and represent a substantial improvement over the results obtained from B3LYP.
WATERMARKING ON COMPRESSED DATA INTEGRATING CONVOLUTION CODING IN INTEGER WAVELETS
Authors: MAITY SANTI P. , DELPHA CLAUDE , BOYER RÉMY
Published: September 2012

This paper explores the scope of integer wavelets in watermarking on compressed image with the aid of convolution coding as channel coding. Convolution coding is applied on compressed host data, instead of its direct application on watermark signal as used widely for robustness improvement in conventional system. Two-fold advantages, namely flexibility in watermarking through the creation of redundancy on the compressed data as well as protection of watermark information from additive white Gaussian noise (AWGN) attack are achieved. Integer wavelet is used to decompose the encoded compressed data that leads to lossless processing and creation of correlation among the host samples due to its mathematical structure. Watermark information is then embedded using dither modulation (DM)-based quantization index modulation (QIM). The relative gain in imperceptibility and robustness performance are reported for direct watermark embedding on entropy decoded host, using repetition code, convolution code, and finally the combined use of channel codes and integer wavelets. Simulation results show that 6.24 dB (9.50 dB) improvement in document-to-watermark ratio (DWR) at watermark power 12.73 dB (16.81 dB) and 15 dB gain in noise power for watermark decoding at bit error rate (BER) of 10-2 are achieved, respectively over direct watermarking on entropy decoded data.
ACCELERATING GENERALIZED ITERATIVE SCALING BASED ON STAGGERED AITKEN METHOD FOR ON-LINE CONDITIONAL RANDOM FIELDS
Authors: YANG HEE-DEOK , SUK HEUNG-IL , LEE SEONG-WHAN
Published: September 2012

In this paper, a convergent method based on Generalized Iterative Scaling (GIS) with staggered Aitken acceleration is proposed to estimate the parameters for an on-line Conditional Random Field (CRF). The staggered Aitken acceleration method, which alternates between the acceleration and non-acceleration steps, ensures computational simplicity when analyzing incomplete data. The proposed method has the following advantages: (1) It can approximate parameters close to the empirical optimum in a single pass through the training examples; (2) It can reduce the computing time by approximating the Jacobian matrix of the mapping function and estimating the relation between the Jacobian and Hessian in order to replace the inverse of the objective function's Hessian matrix. We show the convergence of the penalized GIS based on the staggered Aitken acceleration method, compare its speed of convergence with those of other stochastic optimization methods, and illustrate experimental results with two public datasets.
SYNTHESIS AND PROPERTY OF MULTIFUNCTIONAL Fe3O4@SiO2@CeO2@Au COMPOSITE MICROSPHERES
Authors: WANG YANG , SUN HAORAN , ZHANG TONG , SHEN YUHUA , ZHANG JIAN , XIA JIALING , XIE ANJIAN
Published: September 2012

In this paper, Fe3O4@SiO2@CeO2@Au core/shell microspheres were synthesized through hydrolysis and solvothermal processes. The results indicated that the magnetic Fe3O4 cores were well wrapped by the coating layer of SiO2/CeO2 with a thickness of 50 nm, and Au nanoparticles with 35 nm in diameter were attached on the shell. The microspheres showed a monodispersity and superparamagnetism. The composites showed excellent ability to absorb a wide range of wavelengths including visible and NIR region (from 250 nm to 800 nm), making it a potential full solar spectrum response photocatalyst for sunlight applications.
PHASE EVOLUTION AND MICROWAVE DIELECTRIC PROPERTIES OF (Li0.5Bi0.5)(W1-xMox)O4(0.0 ≤ x ≤ 1.0) CERAMICS WITH ULTRA-LOW SINTERING TEMPERATURES
Authors: ZHOU DI , GUO JING , YAO XI , PANG LI-XIA , QI ZE-MING , SHAO TAO
Published: September 2012

The ( Li0.5Bi0.5)( W1-xMox) O4(0.0 ≤ x ≤ 1.0) ceramics were prepared via the solid state reaction method. The sintering temperature decreased almost linearly from 755°C for ( Li0.5Bi0.5) WO4to 560°C for ( Li0.5Bi0.5) MoO4. When the x≤0.3, a wolframite solid solution can be formed. For x = 0.4 and x = 0.6 compositions, both the wolframite and scheelite phases can be formed from the X-ray diffraction analysis, while two different kinds of grains can be revealed from the scanning electron microscopy and energy-dispersive X-ray spectrometer results. High performance of microwave dielectric properties were obtained in the (Li0.5Bi0.5)(W0.6Mo0.4)O4ceramic sintered at 620°C with a relative permittivity of 31.5, a Qf value of 8500 GHz (at 8.2 GHz), and a temperature coefficient value of +20 ppm/°C. Complex dielectric spectra of pure (Li0.5Bi0.5)WO4ceramic gained from the infrared spectra were extrapolated down to microwave range, and they were in good agreement with the measured values. The ( Li0.5Bi0.5)( W1-xMox) O4(0.0 ≤ x ≤ 1.0) ceramics might be promising for low temperature co-fired ceramic technology.
OPTIMAL SEMI-ONLINE ALGORITHMS FOR m-BATCH-MACHINE FLOW SHOP SCHEDULING
Authors: LIU MING , CHU CHENGBIN
Published: September 2012

This paper deals with semi-online scheduling on m-batch-machine flow shop. The objective is to minimize the makespan. A parallel batch processing machine can handle up to B jobs simultaneously. We study an unbounded model where B = ∞. The jobs that are processed together construct a batch, and all jobs in a batch start and complete at the same time. The processing time of a batch is given by the longest processing time of any job in the batch. The problem is online in the sense that jobs arrive over time. Let pi, j(i = 1,…,m) denote the processing time of job Jj on machines Mi, respectively. Let Jj+1 be the following job of Jj in a job instance. We study semi-online problem with jobs' nondecreasing processing times. We focus on the case where p1, j = ⋯ = pm, j for i = 1, …, m and pi, j+1 ≥ βpi, j (β ≥ 1). For this problem, we propose an optimal algorithm [Formula: see text] with a competitive ratio [Formula: see text].
AXIOMATIC CHARACTERIZATION OF THE ANTIMEDIAN FUNCTION ON PATHS AND HYPERCUBES
Authors: BALAKRISHNAN KANNAN , CHANGAT MANOJ , MULDER HENRY MARTYN , SUBHAMATHI AJITHA R.
Published: September 2012

An antimedian of a profile π = (x1, x2, …, xk) of vertices of a graph G is a vertex maximizing the sum of the distances to the elements of the profile. The antimedian function is defined on the set of all profiles on G and has as output the set of antimedians of a profile. It is a typical location function for finding a location for an obnoxious facility. The 'converse' of the antimedian function is the median function, where the distance sum is minimized. The median function is well studied. For instance it has been characterized axiomatically by three simple axioms on median graphs. The median function behaves nicely on many classes of graphs. In contrast the antimedian function does not have a nice behavior on most classes. So a nice axiomatic characterization may not be expected. In this paper such a characterization is obtained for two classes of graphs on which the antimedian is well behaved: paths and hypercubes.
A NOTE ON BALANCED HOWELL ROTATIONS FOR TWIN PRIME POWER TYPE
Authors: KIM JOONMO , SHENG LI
Published: September 2012

The balanced Howell rotation is a tournament design for bridge. In this note, we show that it exists for n teams where n - 1 is a product of twin prime powers and n ≤ 1020.
PIP
Authors: Gabale Vijay , Chebrolu Kameswari , Raman Bhaskaran , Bijwe Sagar
Published: September 2012

In this article, we consider the goal of achieving high throughput in a wireless sensor network. Our work is set in the context of those wireless sensor network applications which collect and transfer bulk data. We present PIP (Packets in Pipe), a MAC primitive for use by the transport module to achieve high throughput. PIP has a unique set of features: (a) it is a multihop connection-oriented primitive, (b) it is TDMA based, (c) it uses multiple radio channels, and (d) it is centrally controlled. This represents a significant shift from prior MAC protocols for bulk data transfer.

PIP has several desirable properties: (a) its throughput degrades only slightly with increasing number of hops, (b) it is robust to variable wireless error rates, (c) it performs well even without any flow control, and (d) requires only small queue sizes to operate well. We substantiate these properties with a prototype implementation of PIP on the Tmote-Sky CC2420-based platform. PIP achieves about eleven times better throughput than the state-of-the-art prior work, over a network depth of 24 hops. We also show that PIP can be interagted with duty cycling, and that PIP can support streaming data from/to flash at little overhead.
A-MAC
Authors: Dutta Prabal , Dawson-Haggerty Stephen , Chen Yin , Liang Chieh-Jan Mike , Terzis Andreas
Published: September 2012

We present A-MAC, a receiver-initiated link layer for low-power wireless networks that supports several services under a unified architecture, and does so more efficiently and scalably than prior approaches. A-MAC's versatility stems from layering unicast, broadcast, wakeup, pollcast, and discovery above a single, flexible synchronization primitive. A-MAC's efficiency stems from optimizing this primitive and with it the most consequential decision that a low-power link makes: whether to stay awake or go to sleep after probing the channel. Today's receiver-initiated protocols require more time and energy to make this decision, and they exhibit worse judgment as well, leading to many false positives and negatives, and lower packet delivery ratios. A-MAC begins to make this decision quickly, and decides more conclusively and correctly in both the negative and affirmative. A-MAC's scalability comes from reserving one channel for the initial handshake and different channels for data transfer. Our results show that: (i) a unified implementation is possible; (ii) A-MAC's idle listening power increases by just 1.12× under interference, compared to 17.3× for LPL and 54.7× for RI-MAC; (iii) A-MAC offers high single-hop delivery ratios; (iv) network wakeup is faster and more channel efficient than LPL; and (v) collection routing performance exceeds the state-of-the-art.
Achieving long-term operation with a capacitor-driven energy storage and sharing network
Authors: Zhu Ting , Gu Yu , He Tian , Zhang Zhi-Li
Published: September 2012

Energy is the most precious resource in sensor networks. The ability to move energy around makes it feasible to build distributed energy storage systems that can robustly extend the lifetime of networked sensor systems.
eShare
supports the concept of
energy sharing
among multiple embedded sensor devices by providing designs for
energy routers
(i.e., energy storage and routing devices) and related energy access and network protocols. In a nutshell, energy routers exchange energy sharing control information using their data network while sharing energy freely among connected embedded sensor devices using their energy network. To improve sharing efficiency subject to energy leakage, we develop an effective energy charging and discharging mechanism using an array of ultra-capacitors as the main component of an energy router. We extensively evaluate our system under seven real-world settings. Results indicate our charging and discharging control can effectively minimize the energy leaked away. Moreover, the energy sharing protocol can quantitatively share 113J energy with 96.82% accuracy in less than 2 seconds.
Radio link quality estimation in wireless sensor networks
Authors: Baccour Nouha , Koubâa Anis , Mottola Luca , Zúñiga Marco Antonio , Youssef Habib , Boano Carlo Alberto , Alves Mário
Published: September 2012

Radio link quality estimation in Wireless Sensor Networks (WSNs) has a fundamental impact on the network performance and also affects the design of higher-layer protocols. Therefore, for about a decade, it has been attracting a vast array of research works. Reported works on link quality estimation are typically based on different assumptions, consider different scenarios, and provide radically different (and sometimes contradictory) results. This article provides a comprehensive survey on related literature, covering the characteristics of low-power links, the fundamental concepts of link quality estimation in WSNs, a taxonomy of existing link quality estimators, and their performance analysis. To the best of our knowledge, this is the first survey tackling in detail link quality estimation in WSNs. We believe our efforts will serve as a reference to orient researchers and system designers in this area.
The Goldilocks estimate
Authors: Armour Phillip G.
Published: September 2012

Balancing two extremes in project estimation.
The tyranny of the clock
Authors: Sutherland Ivan
Published: September 2012

Promoting a clock-free paradigm that fits everything learned about programming since Turing.
Toward higher precision
Authors: Ratzel Rick , Greenstreet Rodney
Published: September 2012

An introduction to PTP and its significance to NTP practitioners.
Fault injection in production
Authors: Allspaw John
Published: September 2012

Making the case for resilience testing.
A generation lost in the bazaar
Authors: Kamp Poul-Henning
Published: September 2012

Quality happens only when someone is responsible for it.
Experiments in social computation
Authors: Kearns Michael
Published: September 2012

Human subjects perform a computationally wide range of tasks from only local, networked interactions.
Internet voting in the U.S.
Authors: Simons Barbara , Jones Douglas W.
Published: September 2012

Internet voting is unachievable for the foreseeable future and therefore not inevitable.
A few useful things to know about machine learning
Authors: Domingos Pedro
Published: September 2012

Tapping into the "folk knowledge" needed to advance machine learning applications.
Spherical cubes
Authors: Kindler Guy , Rao Anup , O'Donnell Ryan , Wigderson Avi
Published: September 2012

Foam problems are about how to best partition space into bubbles of minimal surface area. We investigate the case where one unit-volume bubble is required to tile
d
-dimensional space in a periodic fashion according to the standard, cubical lattice. While a cube requires surface area 2
d
, we construct such a bubble having surface area very close to that of a sphere; that is, proportional to √d (the minimum possible even without the constraint of being periodic). Our method for constructing this "spherical cube" is inspired by foundational questions in the theory of computation related to the concept of hardness amplification. Our methods give new algorithms for "coordinated discretization" of high-dimensional data points, which have near-optimal noise resistance. We also provide the most efficient known cubical foam in three dimensions.
Hybrid Matching Algorithm for Personal Names
Authors: Varol Cihan , Bayrak Coskun
Published: September 2012

Companies acquire personal information from phone, World Wide Web, or email in order to sell or send an advertisement about their product. However, when this information is acquired, moved, copied, or edited, the data may lose its quality. Often, the use of data administrators or a tool that has limited capabilities to correct the mistyped information can cause many problems. Moreover, most of the correction techniques are particularly implemented for the words used in daily conversations. Since personal names have different characteristics compared to general text, a hybrid matching algorithm (PNRS) which employs phonetic encoding, string matching and statistical facts to provide a possible candidate for misspelled names is developed. At the end, the efficiency of the proposed algorithm is compared with other well known spelling correction techniques.
Multi-resource fair queueing for packet processing
Authors: Ghodsi Ali , Sekar Vyas , Zaharia Matei , Stoica Ion
Published: September 2012

Middleboxes are ubiquitous in today's networks and perform a variety of important functions, including IDS, VPN, firewalling, and WAN optimization. These functions differ vastly in their requirements for hardware resources (
e.g.
, CPU cycles and memory bandwidth). Thus, depending on the functions they go through, different flows can consume different amounts of a middlebox's resources. While there is much literature on weighted fair sharing of link bandwidth to isolate flows, it is unclear how to schedule
multiple
resources in a middlebox to achieve similar guarantees. In this paper, we analyze several natural packet scheduling algorithms for multiple resources and show that they have undesirable properties. We propose a new algorithm, Dominant Resource Fair Queuing (DRFQ), that retains the attractive properties that fair sharing provides for one resource. In doing so, we generalize the concept of virtual time in classical fair queuing to multi-resource settings. The resulting algorithm is also applicable in other contexts where several resources need to be multiplexed in the time domain.
Making middleboxes someone else's problem
Authors: Sherry Justine , Hasan Shaddi , Scott Colin , Krishnamurthy Arvind , Ratnasamy Sylvia , Sekar Vyas
Published: September 2012

Modern enterprises almost ubiquitously deploy middlebox processing services to improve security and performance in their networks. Despite this, we find that today's middlebox infrastructure is expensive, complex to manage, and creates new failure modes for the networks that use them. Given the promise of cloud computing to decrease costs, ease management, and provide elasticity and fault-tolerance, we argue that middlebox processing can benefit from outsourcing the cloud. Arriving at a feasible implementation, however, is challenging due to the need to achieve functional equivalence with traditional middlebox deployments without sacrificing performance or increasing network complexity.

In this paper, we motivate, design, and implement APLOMB, a practical service for outsourcing enterprise middlebox processing to the cloud.

Our discussion of APLOMB is data-driven, guided by a survey of 57 enterprise networks, the first large-scale academic study of middlebox deployment. We show that APLOMB solves real problems faced by network administrators, can outsource over 90% of middlebox hardware in a typical large enterprise network, and, in a case study of a real enterprise, imposes an average latency penalty of 1.1ms and median bandwidth inflation of 3.8%.
HyperDex
Authors: Escriva Robert , Wong Bernard , Sirer Emin Gün
Published: September 2012

Distributed key-value stores are now a standard component of high-performance web services and cloud computing applications. While key-value stores offer significant performance and scalability advantages compared to traditional databases, they achieve these properties through a restricted API that limits object retrieval---an object can only be retrieved by the (primary and only) key under which it was inserted. This paper presents HyperDex, a novel distributed key-value store that provides a unique
search
primitive that enables queries on secondary attributes. The key insight behind HyperDex is the concept of
hyperspace hashing
in which objects with multiple attributes are mapped into a multidimensional hyperspace. This mapping leads to efficient implementations not only for retrieval by primary key, but also for partially-specified secondary attribute searches and range queries. A novel chaining protocol enables the system to achieve strong consistency, maintain availability and guarantee fault tolerance. An evaluation of the full system shows that HyperDex is 12-13x faster than Cassandra and MongoDB for finding partially specified objects. Additionally, HyperDex achieves 2-4x higher throughput for
get
/
put
operations.
Spinal codes
Authors: Perry Jonathan , Iannucci Peter A. , Fleming Kermin E. , Balakrishnan Hari , Shah Devavrat
Published: September 2012

Spinal codes are a new class of rateless codes that enable wireless networks to cope with time-varying channel conditions in a natural way, without requiring any explicit bit rate selection. The key idea in the code is the sequential application of a pseudo-random hash function to the message bits to produce a sequence of coded symbols for transmission. This encoding ensures that two input messages that differ in even one bit lead to very different coded sequences after the point at which they differ, providing good resilience to noise and bit errors. To decode spinal codes, this paper develops an approximate maximum-likelihood decoder, called the
bubble decoder
, which runs in time polynomial in the message size and achieves the Shannon capacity over both additive white Gaussian noise (AWGN) and binary symmetric channel (BSC) models. Experimental results obtained from a software implementation of a linear-time decoder show that spinal codes achieve higher throughput than fixed-rate LDPC codes, rateless Raptor codes, and the layered rateless coding approach of Strider, across a range of channel conditions and message sizes. An early hardware prototype that can decode at 10 Mbits/s in FPGA demonstrates that spinal codes are a practical construction.
Distributed content storage for just-in-time streaming
Authors: Dandapat Sourav Kumar , Jain Sanyam , Choudhury Romit Roy , Ganguly Niloy
Published: September 2012

We propose a content distribution strategy over municipal WiFi networks where Access Points (APs) collaboratively cache popular multimedia content, and disseminate them in a manner that each mobile device has the portion of the content
just-in-time
for playback. If successful, we envision that a child will be able to seamlessly watch a movie in a car, as her tablet downloads different parts of the movie over different WiFi APs at different times.
PaDIS emulator
Authors: Poese Ingmar , Frank Benjamin , Knight Simon , Semmler Niklas , Smaragdakis Georgios
Published: September 2012

We present PaDIS Emulator, a fully automated platform to evaluate CDN-ISP collaboration for better content delivery, traffic engineering, and cost reduction. The PaDIS Emulator enables researchers as well as CDN and ISP operators to evaluate the benefits of collaboration using their own operational networks, configuration, and cost functions.

The PaDIS Emulator consists of three components: the network emulation, the collaboration mechanism, and the performance monitor. These layers provide scalable emulation of the interaction between an ISP or a number of ISPs with multiple CDNs and vice versa. PaDIS Emulator design is flexible in order to implement a wide range of collaboration mechanisms on virtualized or real hardware, and evaluate them before introduction to operational networks.
Route shepherd
Authors: Gurney Alexander J.T. , Han Xianglong , Li Yang , Loo Boon Thau
Published: September 2012

The Route Shepherd tool demonstrates applications of choosing between routing protocol configurations on the basis of rigorously-supported theory. Splitting the configuration space into equivalence classes allows the identification of which parameter combinations lead to protocol stability, and which do not. This ahead-of-time analysis generates a predicate, in the form of a combination of linear integer inequalities, which can be used in several complementary ways by downstream applications. Examples presented include warning operators about errors in advance, recovery from protocol oscillation, plotting a series of safe parameter changes, and understanding the dynamics of the routing system.
A frequency adjustment architecture for energy efficient router
Authors: Fu Wenliang , Song Tian
Published: September 2012

With the rapid expansion of customer population and link bandwidth, energy expenditures of the Internet have been rising dramatically. To gain energy efficiency, we propose a novel router architecture, which allows each of its modules to adjust frequency according to traffic loads. Several modulation strategies are also discussed to ensure dwell time on low energy states and reduce blind switches. Our preliminary results show that the frequency adjustment router could save up to 40% of the total energy consumption.
DeTail
Authors: Zats David , Das Tathagata , Mohan Prashanth , Borthakur Dhruba , Katz Randy
Published: September 2012

Web applications have now become so sophisticated that rendering a typical page may require hundreds of intra-datacenter flows. At the same time, web sites must meet strict page creation deadlines of 200-300
ms
to satisfy user demands for interactivity. Long-tailed flow completion times make it challenging for web sites to meet these constraints. They are forced to choose between rendering a subset of the complex page, or delay its rendering, thus missing deadlines and sacrificing either quality or responsiveness. Either option leads to potential financial loss.

In this paper, we present a new cross-layer network stack aimed at reducing the long tail of flow completion times. The approach exploits cross-layer information to reduce packet drops, prioritize latency-sensitive flows, and evenly distribute network load, effectively reducing the long tail of flow completion times. We evaluate our approach through NS-3 based simulation and Click-based implementation demonstrating our ability to consistently reduce the tail across a wide range of workloads. We often achieve reductions of over 50% in 99.9

th

percentile flow completion times.
Anatomy of a large european IXP
Authors: Ager Bernhard , Chatzis Nikolaos , Feldmann Anja , Sarrar Nadi , Uhlig Steve , Willinger Walter
Published: September 2012

The largest IXPs carry on a daily basis traffic volumes in the petabyte range, similar to what some of the largest global ISPs reportedly handle. This little-known fact is due to a few hundreds of member ASes exchanging traffic with one another over the IXP's infrastructure. This paper reports on a first-of-its-kind and in-depth analysis of one of the largest IXPs worldwide based on nine months' worth of sFlow records collected at that IXP in 2011.

A main finding of our study is that the number of actual peering links at this single IXP exceeds the number of total AS links of the peer-peer type in the entire Internet known as of 2010! To explain such a surprisingly rich peering fabric, we examine in detail this IXP's ecosystem and highlight the diversity of networks that are members at this IXP and connect there with other member ASes for reasons that are similarly diverse, but can be partially inferred from their business types and observed traffic patterns. In the process, we investigate this IXP's traffic matrix and illustrate what its temporal and structural properties can tell us about the member ASes that generated the traffic in the first place. While our results suggest that these large IXPs can be viewed as a microcosm of the Internet ecosystem itself, they also argue for a re-assessment of the mental picture that our community has about this ecosystem.
Measuring and fingerprinting click-spam in ad networks
Authors: Dave Vacha , Guha Saikat , Zhang Yin
Published: September 2012

Advertising plays a vital role in supporting free websites and smartphone apps. Click-spam, i.e., fraudulent or invalid clicks on online ads where the user has no actual interest in the advertiser's site, results in advertising revenue being misappropriated by click-spammers. While ad networks take active measures to block click-spam today, the effectiveness of these measures is largely unknown. Moreover, advertisers and third parties have no way of independently estimating or defending against click-spam.

In this paper, we take the first systematic look at click-spam. We propose the first methodology for advertisers to independently measure click-spam rates on their ads. We also develop an automated methodology for ad networks to proactively detect different simultaneous click-spam attacks. We validate both methodologies using data from major ad networks. We then conduct a large-scale measurement study of click-spam across ten major ad networks and four types of ads. In the process, we identify and perform in-depth analysis on seven ongoing click-spam attacks not blocked by major ad networks at the time of this writing. Our findings highlight the severity of the click-spam problem, especially for mobile ads.
FairCloud
Authors: Popa Lucian , Kumar Gautam , Chowdhury Mosharaf , Krishnamurthy Arvind , Ratnasamy Sylvia , Stoica Ion
Published: September 2012

The network, similar to CPU and memory, is a critical and shared resource in the cloud. However, unlike other resources, it is neither shared proportionally to payment, nor do cloud providers offer minimum guarantees on network bandwidth. The reason networks are more difficult to share is because the network allocation of a virtual machine (VM)
X
depends not only on the VMs running on the same machine with
X
, but also on the other VMs that
X
communicates with and the cross-traffic on each link used by
X
. In this paper, we start from the above requirements--payment proportionality and minimum guarantees--and show that the network-specific challenges lead to fundamental tradeoffs when sharing cloud networks. We then propose a set of properties to explicitly express these tradeoffs. Finally, we present three allocation policies that allow us to navigate the tradeoff space. We evaluate their characteristics through simulation and testbed experiments to show that they can provide minimum guarantees and achieve better proportionality than existing solutions.
JMB
Authors: Rahul Hariharan Shankar , Kumar Swarun , Katabi Dina
Published: September 2012

We present joint multi-user beamforming (JMB), a system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind JMB is a new low-overhead technique for synchronizing the phase of multiple transmitters in a distributed manner. The design allows a wireless LAN to scale its throughput by continually adding more APs on the same channel. JMB is implemented and tested with both software radio clients and off-the-shelf 802.11n cards, and evaluated in a dense congested deployment resembling a conference room. Results from a 10-AP software-radio testbed show a linear increase in network throughput with a median gain of 8.1 to 9.4x. Our results also demonstrate that JMB's joint multi-user beamforming can provide throughput gains with unmodified 802.11n cards.
Energino
Authors: Riggio Roberto , Sengul Cigdem , Mabell Gomez Karina , Rasheed Tinku
Published: September 2012

The energy wasted in wireless networks is a serious concern and the main challenge lies in determining when and where the energy is wasted. In this demo, we present
Energino
, an energy measurement and control system designed to deliver high performance while remaining a cheap solution.
Demo
Authors: Zhang Xi , Ansari Junaid , Mähönen Petri
Published: September 2012

A rapid reconfiguration of medium access scheme is required in order to achieve runtime performance optimization for dynamic spectrum access and fulfilling varying Quality of Service (QoS) demands. We have developed TRUMP, a toolchain which allows composing MAC solutions at runtime. In this demonstration, we will show how MAC reconfiguration can be achieved efficiently using TRUMP. Inspired by the optimum route calculation method used in car navigation systems, the compiler toolchain in TRUMP realizes an appropriate MAC solution at runtime. TRUMP allows expressing various types of constraints and options such as speed, energy consumption and packet delivery rate which leads to different MAC compositions. The live demonstration of MAC reconfiguration will be carried out on WARP SDR platform.
Picasso
Authors: Hong Steven , Mehlman Jeffrey , Katti Sachin
Published: September 2012

Many applications can benefit from the capability to simultaneously and independently use arbitrarily sized but separate spectrum fragments with a single radio and antenna. By this capability we mean that the radio can simultaneously transmit, simultaneously receive, or simultaneously transmit and receive on arbitrary but separate spectrum fragments. For example, we can use it for spectrum aggregation in fragmented ISM bands as shown in as shown in Fig. 2(A). A WiFi AP can run independent OFDM PHY and CSMA MAC protocols on two WiFi channels to simultaneously serve two legacy WiFi clients assigned to different channels and achieve significantly higher throughput than a legacy AP that is restricted to use only one channel at a time. Similarly, a WiFi client radio with such a capability can use it to simultaneously connect to multiple WiFi APs on different channels and obtain a much higher aggregate throughput than current radios that can transmit or receive on only one channel at a time.
Dismantling intrusion prevention systems
Authors: Niemi Olli-Pekka , Levomäki Antti , Manner Jukka
Published: September 2012

This paper introduces a serious security problem that people believe has been fixed, but which is still very much existing and evolving, namely evasions. We describe how protocols can still be misused to fool network security devices, such as intrusion prevention systems.
Scalable software defined network controllers
Authors: Voellmy Andreas , Wang Junchang
Published: September 2012

Software defined networking (SDN) introduces centralized controllers to dramatically increase network programmability. The simplicity of a logical centralized controller, however, can come at the cost of control-plane scalability. In this demo, we present McNettle, an extensible SDN control system whose control event processing throughput scales with the number of system CPU cores and which supports control algorithms requiring globally visible state changes occurring at flow arrival rates. Programmers extend McNettle by writing event handlers and background programs in a high-level functional programming language extended with shared state and memory transactions. We implement our framework in Haskell and leverage the multicore facilities of the Glasgow Haskell Compiler (GHC) and runtime system. Our implementation schedules event handlers, allocates memory, optimizes message parsing and serialization, and reduces system calls in order to optimize cache usage, OS processing, and runtime system overhead. Our experiments show that McNettle can serve up to 5000 switches using a single controller with 46 cores, achieving throughput of over 14 million flows per second, near-linear scaling up to 46 cores, and latency under 200
μs
for light loads and 10 ms with loads consisting of up to 5000 switches.
First insights from a mobile honeypot
Authors: Wählisch Matthias , Trapp Sebastian , Keil Christian , Schönfelder Jochen , schmidt Thomas C. , Schiller Jochen
Published: September 2012

Computer systems are commonly attacked by malicious transport contacts. We present a comparative study that analyzes to what extent those attacks depend on the network access, in particular if an adversary targets specifically on mobile or non-mobile devices. Based on a mobile honeypot that extracts first statistical results, our findings indicate that a few topological domains of the Internet have started to place particular focus on attacking mobile networks.
Policy transformation in software defined networks
Authors: Kang Nanxi , Reich Joshua , Rexford Jennifer , Walker David
Published: September 2012

A Software Defined Network (SDN) enforces network-wide policies by installing packet-handling rules across a distributed collection of switches. Today's SDN platforms force programmers to decide how to decompose a high-level policy into the low-level rules in each switch. We argue that future SDN platforms should support automatic transformation of policies by moving, merging, or splitting rules across multiple switches. This would simplify programming by allowing programs written on one abstract switch to run over a more complex network topology, and simplify analysis by consolidating a policy spread over multiple switches into a single list of rules. This poster presents our ongoing work on a sound and complete set of axioms for policy transformation, to enable rewriting of rules across multiple switches while preserving the forwarding policy. These axioms are invaluable for creating and analyzing algorithms for optimizing the rewriting of rules.
Abstractions for network update
Authors: Reitblatt Mark , Foster Nate , Rexford Jennifer , Schlesinger Cole , Walker David
Published: September 2012

Configuration changes are a common source of instability in networks, leading to outages, performance disruptions, and security vulnerabilities. Even when the initial and final configurations are correct, the update process itself often steps through intermediate configurations that exhibit incorrect behaviors. This paper introduces the notion of consistent network updates---updates that are guaranteed to preserve well-defined behaviors when transitioning mbetween configurations. We identify two distinct consistency levels, per-packet and per-flow, and we present general mechanisms for implementing them in Software-Defined Networks using switch APIs like OpenFlow. We develop a formal model of OpenFlow networks, and prove that consistent updates preserve a large class of properties. We describe our prototype implementation, including several optimizations that reduce the overhead required to perform consistent updates. We present a verification tool that leverages consistent updates to significantly reduce the complexity of checking the correctness of network control software. Finally, we describe the results of some simple experiments demonstrating the effectiveness of these optimizations on example applications.
A case for a coordinated internet video control plane
Authors: Liu Xi , Dobrian Florin , Milner Henry , Jiang Junchen , Sekar Vyas , Stoica Ion , Zhang Hui
Published: September 2012

Video traffic already represents a significant fraction of today's traffic and is projected to exceed 90% in the next five years. In parallel, user expectations for a high quality viewing experience (e.g., low startup delays, low buffering, and high bitrates) are continuously increasing. Unlike traditional workloads that either require low latency (e.g., short web transfers) or high average throughput (e.g., large file transfers), a high quality video viewing experience requires
sustained
performance over
extended
periods of time (e.g., tens of minutes). This imposes fundamentally different demands on content delivery infrastructures than those envisioned for traditional traffic patterns. Our large-scale measurements over 200 million video sessions show that today's delivery infrastructure fails to meet these requirements: more than 20% of sessions have a rebuffering ratio ≥ 10% and more than 14% of sessions have a video startup delay ≥ 10s. Using measurement-driven insights, we make a case for a video control plane that can use a global view of client and network conditions to dynamically optimize the video delivery in order to provide a high quality viewing experience despite an unreliable delivery infrastructure. Our analysis shows that such a control plane can potentially improve the rebuffering ratio by up to 2× in the average case and by more than one order of magnitude under stress.
LIFEGUARD
Authors: Katz-Bassett Ethan , Scott Colin , Choffnes David R. , Cunha Ítalo , Valancius Vytautas , Feamster Nick , Madhyastha Harsha V. , Anderson Thomas , Krishnamurthy Arvind
Published: September 2012

The Internet was designed to always find a route if there is a policy-compliant path. However, in many cases, connectivity is disrupted despite the existence of an underlying valid path. The research community has focused on short-term outages that occur during route convergence. There has been less progress on addressing avoidable long-lasting outages. Our measurements show that long-lasting events contribute significantly to overall unavailability.

To address these problems, we develop
LIFEGUARD
, a system for automatic failure localization and remediation.
LIFEGUARD
uses active measurements and a historical path atlas to locate faults, even in the presence of asymmetric paths and failures. Given the ability to locate faults, we argue that the Internet protocols should allow edge ISPs to steer traffic to them around failures, without requiring the involvement of the network causing the failure. Although the Internet does not explicitly support this functionality today, we show how to approximate it using carefully crafted BGP messages.
LIFEGUARD
employs a set of techniques to reroute around failures with low impact on working routes. Deploying
LIFEGUARD
on the Internet, we find that it can effectively route traffic around an AS without causing widespread disruption.