bluuebunny/crossref_metadata_2025 huggingface dataset:
c-Through
Authors: Wang Guohui , Andersen David G. , Kaminsky Michael , Papagiannaki Konstantina , Ng T.S. Eugene , Kozuch Michael , Ryan Michael
Published: October 2012

Data-intensive applications that operate on large volumes of data have motivated a fresh look at the design of data center networks. The first wave of proposals focused on designing pure packet-switched networks that provide full bisection bandwidth. However, these proposals significantly increase network complexity in terms of the number of links and switches required and the restricted rules to wire them up. On the other hand, optical circuit switching technology holds a very large bandwidth advantage over packet switching technology. This fact motivates us to explore how optical circuit switching technology could benefit a data center network. In particular, we propose a hybrid packet and circuit switched data center network architecture (or HyPaC for short) which augments the traditional hierarchy of packet switches with a high speed, low complexity, rack-to-rack optical circuit-switched network to supply high bandwidth to applications. We discuss the fundamental requirements of this hybrid architecture and their design options. To demonstrate the potential benefits of the hybrid architecture, we have built a prototype system called c-Through. c-Through represents a design point where the responsibility for traffic demand estimation and traffic demultiplexing resides in end hosts, making it compatible with existing packet switches. Our emulation experiments show that the hybrid architecture can provide large benefits to unmodified popular data center applications at a modest scale. Furthermore, our experimental experience provides useful insights on the applicability of the hybrid architecture across a range of deployment scenarios.
Helios
Authors: Farrington Nathan , Porter George , Radhakrishnan Sivasankar , Bazzaz Hamid Hajabdolali , Subramanya Vikram , Fainman Yeshaiahu , Papen George , Vahdat Amin
Published: October 2012

The basic building block of ever larger data centers has shifted from a rack to a modular container with hundreds or even thousands of servers. Delivering scalable bandwidth among such containers is a challenge. A number of recent efforts promise full bisection bandwidth between all servers, though with significant cost, complexity, and power consumption. We present Helios, a hybrid electrical/optical switch architecture that can deliver significant reductions in the number of switching elements, cabling, cost, and power consumption relative to recently proposed data center network architectures. We explore architectural trade offs and challenges associated with realizing these benefits through the evaluation of a fully functional Helios prototype.
An analysis of social network-based Sybil defenses
Authors: Viswanath Bimal , Post Ansley , Gummadi Krishna P. , Mislove Alan
Published: October 2012

Recently, there has been much excitement in the research community over using social networks to mitigate multiple identity, or Sybil, attacks. A number of schemes have been proposed, but they differ greatly in the algorithms they use and in the networks upon which they are evaluated. As a result, the research community lacks a clear understanding of how these schemes compare against each other, how well they would work on real-world social networks with different structural properties, or whether there exist other (potentially better) ways of Sybil defense.

In this paper, we show that, despite their considerable differences, existing Sybil defense schemes work by detecting local communities (i.e., clusters of nodes more tightly knit than the rest of the graph) around a trusted node. Our finding has important implications for both existing and future designs of Sybil defense schemes. First, we show that there is an opportunity to leverage the substantial amount of prior work on general community detection algorithms in order to defend against Sybils. Second, our analysis reveals the fundamental limits of current social network-based Sybil defenses: We demonstrate that networks with well-defined community structure are inherently more vulnerable to Sybil attacks, and that, in such networks, Sybils can carefully target their links in order make their attacks more effective.
The little engine(s) that could
Authors: Pujol Josep M. , Erramilli Vijay , Siganos Georgos , Yang Xiaoyuan , Laoutaris Nikos , Chhabra Parminder , Rodriguez Pablo
Published: October 2012

The difficulty of scaling Online Social Networks (OSNs) has introduced new system design challenges that has often caused costly re-architecting for services like Twitter and Facebook. The complexity of interconnection of users in social networks has introduced new scalability challenges. Conventional vertical scaling by resorting to full replication can be a costly proposition. Horizontal scaling by partitioning and distributing data among multiples servers - e.g. using DHTs - can lead to costly inter-server communication.

We design, implement, and evaluate SPAR, a social partitioning and replication middle-ware that transparently leverages the social graph structure to achieve data locality while minimizing replication. SPAR guarantees that for all users in an OSN, their direct neighbor's data is co-located in the same server. The gains from this approach are multi-fold: application developers can assume local semantics, i.e., develop as they would for a single server; scalability is achieved by adding commodity servers with low memory and network I/O requirements; and redundancy is achieved at a fraction of the cost.

We detail our system design and an evaluation based on datasets from Twitter, Orkut, and Facebook, with a working implementation. We show that SPAR incurs minimum overhead, and can help a well-known open-source Twitter clone reach Twitter's scale without changing a line of its application logic and achieves higher throughput than Cassandra, Facebook's DHT based key-value store database.
SIP overload control
Authors: Wang Yaogong
Published: October 2012

Overload happens in Session Initiation Protocol (SIP) networks when SIP servers have insufficient resources to handle all messages they receive. Under overload, SIP networks suffer from congestion collapse due to its ineffective overload control mechanism. In this paper we propose a backpressure-based SIP overload control mechanism called Bassoon. It consists of two parts: the first part is a provably optimal load balancing algorithm that ensures full utilization of the available network resources. The second part is an end-to-end load control algorithm that intelligently throttles excessive traffic at the edge of the network. We show that, by combining optimal load balancing and end-to-end load control, Bassoon effectively controls overload in SIP networks and outperforms existing schemes in terms of goodput, fairness and responsiveness.
Unbiased sampling in directed social graph
Authors: Wang Tianyi , Chen Yang , Zhang Zengbin , Sun Peng , Deng Beixing , Li Xing
Published: October 2012

Microblogging services, such as Twitter, are among the most important online social networks(OSNs). Different from OSNs such as Facebook, the topology of microblogging service is a directed graph instead of an undirected graph. Recently, due to the explosive increase of population size, graph sampling has started to play a critical role in measurement and characterization studies of such OSNs. However, previous studies have only focused on the unbiased sampling of
undirected
social graphs. In this paper, we study the unbiased sampling algorithm for
directed
social graphs. Based on the traditional Metropolis-Hasting Random Walk (MHRW) algorithm, we propose an unbiased sampling method for
directed
social graphs(USDSG). Using this method, we get the first, to the best of our knowledge, unbiased sample of directed social graphs. Through extensive experiments comparing with the "ground truth" (UNI, obtained through uniform sampling of directed graph nodes), we show that our method can achieve excellent performance in directed graph sampling and the error to UNI is less than 10%.
Contrabass
Authors: Yoon Sungro
Published: October 2012

A PHY and MAC protocol for MIMO concurrent transmissions, called
Contrabass
, is presented. Concurrent transmissions, also referred to as multi-user MIMO, are simultaneous transmissions by multiple interfering nodes over the same carrier frequency. Concurrent transmissions technique has the potential of mitigating the overhead of MAC protocols by amortizing protocol overhead among multiple packets. However, existing proposals for concurrent transmissions could not achieve this as MIMO channel training and collision avoidance typically involve an expensive process of coordination and control message exchanges. This overhead has made MIMO concurrent transmission Impractical and thus unused in real applications. Contrabass implements simultaneous channel training and optimal transmission control without any coordination. As a result, Contrabass achieves very high aggregate throughput, low delays and scalability even under dynamic environments and outperforms the existing MIMO protocols. This is the first practical implementation of MIMO-based concurrent transmissions. We implemented Contrabass in GNU radios and also in NS-2.
Backpressure-based routing protocol for DTNs
Authors: Dvir Amit , Vasilakos Athanasios V.
Published: October 2012

In this paper we consider an alternative, highly agile In this paper we consider an alternative, highly agile approach called backpressure routing for Delay Tolerant Networks (DTN), in which routing and forwarding decisions are made on a per-packet basis. Using information about queue backlogs, random walk and data packet scheduling nodes can make packet routing and forwarding decisions without the notion of end-to-end routes. To the best of our knowledge, this is the first ever implementation of dynamic backpressure routing in DTNs. Simulation results show that the proposed approach has advantages in terms of DTN networks.
Fair bandwidth allocation in wireless network using max-flow
Authors: Dandapat Sourav Kumar , Mitra Bivas , Ganguly Niloy , Choudhury Romit Roy
Published: October 2012

This paper proposes a fair association scheme between clients and APs in WiFi network, exploiting the hybrid nature of the recent WLAN architecture. We show that such an association outperforms RSSI based schemes in several scenarios, while remaining practical and scalable for wide-scale deployment.
Passive IP traceback
Authors: Yao Guang , Bi Jun , Zhou Zijian
Published: October 2012

IP traceback can be used to find the origin of anonymous traffic; however, Internet-scale IP traceback systems have not been deployed due to a need for cooperation between Internet Service Providers (ISPs). This article presents an Internet-scale Passive IP Trackback (PIT) mechanism that does not require ISP deployment. PIT analyzes the ICMP messages that may scattered to a network telescope as spoofed packets travel from attacker to victim. An Internet route model is then used to help re-construct the attack path. Applying this mechanism to data collected by Cooperative Association for Internet Data Analysis (CAIDA), we found PIT can construct a trace tree from at least one intermediate router in 55.4% the fiercest packet spoofing attacks, and can construct a tree from at least 10 routers in 23.4% of attacks. This initial result shows PIT is a promising mechanism.
SecureAngle
Authors: Xiong Jie , Jamieson Kyle
Published: October 2012

Wireless local area networks play an important role in our everyday lives, at the workplace and at home. However, wireless networks are also relatively vulnerable: physically located off-premises, attackers can circumvent wireless security protocols such as WEP, WPA, and even to some extent WPA2, presenting a security risk to the entire network. To address this problem, we propose
SecureAngle
, a system designed to operate alongside existing wireless security protocols, adding defense in depth. SecureAngle employs multiantenna APs to profile the directions at which a client's signal arrives, using this
angle-of-arrival
information to construct unique
signatures
that identify each client. With these signatures, we are currently investigating how a SecureAngle enabled AP can enable a "virtual fence" that drops frames injected into the network from a client physically located outside a building, and how a SecureAngle-enabled AP can prevent malicious parties from spoofing the link-layer address of legitimate clients.
Autonomous traffic engineering with self-configuring topologies
Authors: Sundaresan Srikanth , Lumezanu Cristian , Feamster Nick , Francois Pierre
Published: October 2012

Network operators use traffic engineering (TE) to control the flow of traffic across their networks. Existing TE methods require manual configuration of link weights or tunnels, which is difficult to get right, or prior knowledge of traffic demands and hence may not be robust to link failures or traffic fluctuations. We present a self-configuring TE scheme, SculpTE, which automatically adapts the network-layer topology to changing traffic demands. SculpTE is responsive, stable, and achieves excellent load balancing.
Accelerometer-assisted 802.11 rate adaptation on mass rapid transit system
Authors: Lai Yu-Jen , Kuo Wei-Hao , Chiu Wan-Ting , Chang Shao-Ting , Wei Hung-Yu
Published: October 2012

In-station Wi-Fi AP deployment provides opportunistic Wi-Fi access in underground Mass Rapid Transit (MRT) system. But such vehicular network faces the obstacle of limited connection time from the MS on the train to the BS at the station. Therefore, maximizing the throughput during the tens of second intervals becomes crucial to overcome such hindrance. To achieve the goal, we propose Accelerometer-Assisted Rate Adaptation (AARA) to divide the motion of the train into four phases; each adopts a specific rate adaptation mechanism. The experiments show that the average throughput of AARA outperforms that of the conventional scheme.
Mobile data offloading
Authors: Lee Kyunghan , Lee Joohyun , Yi Yung , Rhee Injong , Chong Song
Published: October 2012

This is a quantitative study on the performance of 3G mobile data offloading through WiFi networks. We recruited about 100 iPhone users from a metropolitan area and collected statistics on their WiFi connectivity during about a two and half week period in February 2010. We find that a user is in WiFi coverage for 70% of the time on average and the distributions of WiFi connection and disconnection times have a strong heavy-tail tendency with means around 2 hours and 40 minutes, respectively. Using the acquired traces, we run trace-driven simulation to measure offloading efficiency under diverse conditions e.g. traffic types, deadlines and WiFi deployment scenarios. The results indicate that if users can tolerate a two hour delay in data transfer (e.g, video and image up-loads), the network can offload 70% of the total 3G data traffic on average. We also develop a theoretical framework that permits an analytical study of the average performance of offloading. This tool is useful for network providers to obtain a rough estimate on the average performance of offloading for a given inputWiFi deployment condition.
Residual white space distribution-based opportunistic channel access for cognitive radio enabled devices
Authors: Sharma Manuj , Sahoo Anirudha
Published: October 2012

We describe an opportunistic channel access scheme for cognitive radio-enabled secondary nodes (SNs). The proposed scheme uses the residual channel idle time distribution to estimate the transmission duration in the remaining idle time, subject to an acceptable Primary User (PU) interference constraint. The SN then transmits the frames within the estimated duration without further sensing the channel, which reduces sensing overhead. The scheme does not require the SN to continuously sense the channel to keep track of the start of the idle period, thereby conserving energy.
Cone of silence
Authors: Nikolaidis Georgios , Zhushi Astrit , Jamieson Kyle , Karp Brad
Published: October 2012

Dense 802.11 wireless networks present a pressing capacity challenge: users in proximity contend for limited unlicensed spectrum. Directional antennas promise increased capacity by improving the signal-to-interference-plus-noise ratio (SINR) at the receiver, potentially allowing successful decoding of packets at higher bit-rates. Many uses of directional antennas to date have directed high gain between two peers, thus maximizing the strength of the sender's signal reaching the receiver. But in an interference-rich environment, as in dense 802.11 deployments, directional antennas only truly come into their own when they
explicitly null
interference from competing concurrent senders. In this paper, we present Cone of Silence (CoS), a technique that leverages software-steerable directional antennas to improve the capacity of indoor 802.11 wireless networks by adaptively nulling interference. Using
in situ
signal strength measurements that account for the complex propagation environment, CoS derives custom antenna radiation patterns that maximize the strength of the signal arriving at an access point from a sender while nulling inteference from one or more concurrent interferers. CoS leverages multiple antennas, but requires only a single commodity 802.11 radio, thus avoiding the significant processing requirements of decoding multiple concurrent packets. Experiments in an indoor 802.11 deployment demonstrate that CoS improves throughput under interference.
Accelerating SSL with GPUs
Authors: Jang Keon , Han Sangjin , Han Seungyeop , Moon Sue , Park KyoungSoo
Published: October 2012

SSL/TLS is a standard protocol for secure Internet communication. Despite its great success, today's SSL deployment is largely limited to security-critical domains. The low adoption rate of SSL is mainly due to high computation overhead on the server side.

In this paper, we propose Graphics Processing Units (GPUs) as a new source of computing power to reduce the server-side overhead. We have designed and implemented an SSL proxy that opportunistically offloads cryptographic operations to GPUs. The evaluation results show that our GPU implementation of cryptographic operations, RSA, AES, and HMAC-SHA1, achieves high throughput while keeping the latency low. The SSL proxy significantly boosts the throughput of SSL transactions, handling 25.8K SSL transactions per second, and has comparable response time even when overloaded.
An open router virtualization framework using a programmable forwarding plane
Authors: Bozakov Zdravko
Published: October 2012

Network virtualization promises to spur innovation and add flexibility to the Future Internet infrastructure. Routers supporting virtualization allow the deployment of concurrent virtual networks, and can be employed to consolidate resources and improve energy efficiency in data centers. The closed nature of commercial router systems poses a significant problem for research in the field of virtual network architectures. On the other hand, the performance of software-based, open routing solutions is typically limited. In this work we outline an open router virtualization framework utilizing OpenFlow enabled hardware as a fast, programmable forwarding plane.
Caliper
Authors: Ghobadi Monia , Labrecque Martin , Salmon Geoffrey , Aasaraai Kaveh , Hassas Yeganeh Soheil , Ganjali Yashar , Steffan J. Gregory
Published: October 2012

Generating realistic and responsive traffic that reflects different network conditions is a challenging problem associated with performing valid experiments in network testbeds. In this work, we preset Caliper, a highly precise traffic generation tool, built on NetThreads, a flexible platform that we have created for developing packet processing applications on FPGA-based devices and the NetFPGA in particular. We will demonstrate the effect of ad-hoc inter-departure times on a commodity NIC compared to precisely timed inter-departures with Caliper. Both NetThreads and Caliper are available as free software to download.
SoftCast
Authors: Jakubczak Szymon , Katabi Dina
Published: October 2012

The focus of this demonstration is the performance of streaming video over the mobile wireless channel. We compare two schemes: the standard approach to video which transmits H.264/AVC-encoded stream over 802.11-like PHY, and SoftCast -- a clean-slate design for wireless video where the source transmits one video stream that each receiver decodes to a video quality commensurate with its specific instantaneous channel quality.
PixNet
Authors: Perli Samuel David , Ahmed Nabeel , Katabi Dina
Published: October 2012

Given the abundance of cameras and LCDs in today's environment, there exists an untapped opportunity for using these devices for communication. Specifically, cameras can tune to nearby LCDs and use them for network access. The key feature of these LCD-camera links is that they are highly directional and hence enable a form of interference-free wireless communication. This makes them an attractive technology for dense, high contention scenarios. The main challenge, however, to enable such LCD-camera links is to maximize coverage, that is to deliver multiple Mb/s over multi-meter distances, independent of the view angle. To do so, these links need to address unique types of channel distortions, such as perspective distortion and blur.

In this demo, we show how these LCD-camera links can be used to wirelessly transmit information. We present PixNet, an LCD-camera communication system. PixNet generalizes the popular OFDM transmission algorithms to address the unique properties of the LCD-camera link, including perspective distortion and blur. We have built a prototype of PixNet using off-the-shelf LCDs and cameras. In our demo, we will show our prototype communicating data from an LCD to a camera-equipped PC, over multi-meter distances and wide viewing angles.
VMtorrent
Authors: Reich Joshua , Laadan Oren , Brosh Eli , Sherman Alex , Misra Vishal , Nieh Jason , Rubenstein Dan
Published: October 2012

Virtual Appliances (VAs) are Virtual Machines (VMs) geared towards a specific set of tasks. They require little or no configuration, working out-of-the-box. VAs fit neatly into the Cloud Computing paradigm - many copies of an identical machine can be launched in a data center, or home/business users can grab the appliance they need from the cloud to run locally just for so long as required. Companies and projects whose sole offerings are VAs ready for either desktop or data center use [3, 11] attest to the growing popularity of VAs. VMware's Appliance directory alone currently lists over 1400 VAs available for the VMware family of Virtual Machine Monitors (VMMs) [13].

Current VA distribution generally requires download of the complete virtual disk image, only after which the VA can be run. Given that compressed VA sizes run anywhere from several hundred MB to a few GB, there can be significant delays from the time a user decides he/she wants to run a particular VA until the time that VA can be used. These problems are only exacerbated when demand for particular VAs spikes and server bandwidth resources become the distribution bottleneck.
Flexible multimedia content retrieval using InfoNames
Authors: Kumar Arun , Anand Ashok , Akella Aditya , Balachandran Athula , Sekar Vyas , Seshan Srinivasan
Published: October 2012

Multimedia content is a dominant fraction of Internet usage today. At the same time, there is significant heterogeneity in video presentation modes and operating conditions of Internet-enabled devices that access such content. Users are often interested in the content, rather than the specific sources or the formats. The host-centric format of the current Internet does not support these requirements naturally. Neither do the recent data-centric naming proposals, since they rely on naming content based on raw byte-level hashing schemes. We argue that to meet these requirements, enabling content retrieval mechanisms to name and query directly for the underlying information is a good way forward. In addition to decoupling content from available sources and transfer protocols, these "information-aware names" or InfoNames explicitly decouple the information from content presentation factors as well. We envision an InfoName Resolution System (IRS) to resolve location based on InfoNames, while taking into account the operating conditions of devices. In this demo, we present an application to show how InfoNames can serve as presentation-invariant and portable names to fetch video content independent of device capabilities and resource constraints.
No more middlebox
Authors: Lee Jeongkeun , Tourrilhes Jean , Sharma Puneet , Banerjee Sujata
Published: October 2012

Traditionally, in-network services like firewall, proxy, cache, and transcoders have been provided by dedicated hardware middleboxes. A recent trend has been to remove the middleboxes by deploying the network services into switch/router-integrated computing modules or separate server/blade machines. In this abstract, by using a web Ad-insertion application as an example, we demonstrate our in-network processing (INP) framework that orchestrates various computing resources and network devices and enables seamless and efficient deployments of network services.
Source flow
Authors: Chiba Yasunobu , Shinohara Yusuke , Shimonishi Hideyuki
Published: October 2012

Flow-based networks such as OpenFlow-based networks have difficulty handling a large number of flows in a node due to the capacity limitation of search engine devices such as ternary content-addressable memory (TCAM). One typical solution of this problem would be to use MPLS-like tunneling, but this approach spoils the advantage of flow-by-flow path selection for load-balancing or QoS. We demonstrate a method named "Source Flow" that allows us to handle a huge amount of flows without changing the granularity of flows. By using our method, expensive and power consuming search engine devices can be removed from the core nodes, and the network can grow pretty scalable. In our demo, we construct a small network that consists of small number of OpenFlow switches, a single OpenFlow controller, and end-hosts. The hosts generate more than one million flows simultaneously and the flows are controlled on a per-flow-basis. All active flows are monitored and visualized on a user interface and the user interface allows audiences to confirm if our method is feasible and deployable.
Experimenting software radio with the Sora platform
Authors: Zhang Jiansong , Tan Kun , Xiang Sen , Yin Qiufeng , Luo Qi , He Yong , Fang Ji , Zhang Yongguang
Published: October 2012

Sora is a fully programmable, high performance software radio platform based on commodity general-purpose PC. In this demonstration, we illustrate the main features of the Sora platform that provide researchers flexible and powerful means to conduct wireless experiments at different levels with various goals. Specifically, the demonstrator will show four useful applications for wireless research that are built based on the Sora platform: 1) A capture tool that allows one to take a snapshot on a wireless channel; 2) a signal generation tool that allows one to transmit arbitrary baseband wave-form over the air, from a monophonic tone to a complex modulated frame; 3) an on-line real-time receiving application that uses the Sora User-Mode Extension; and 4) a fully featured Software radio WiFi driver (SoftWiFi) that can seamlessly inter-operate with commercial WiFi cards.
Circumventing censorship with collage
Authors: Burnett Sam , Feamster Nick , Vempala Santosh
Published: October 2012

Oppressive regimes and even democratic governments restrict Internet access. Existing anti-censorship systems often require users to connect through proxies, but these systems are relatively easy for a censor to discover and block. We explore a possible next step in the censorship arms race: rather than relying on a single system or set of proxies to circumvent censorship firewalls, we use the vast deployment of sites that host user-generated content to breach these firewalls. We have developed Collage, which allows users to exchange messages through hidden channels in sites that host user-generated content. To send a message, a user embeds it into cover traffic and posts the content on some site, where receivers retrieve this content. Collage makes it difficult for a censor to monitor or block these messages by exploiting the sheer number of sites where users can exchange messages and the variety of ways that a message can be hidden.

We have built a censorship-resistant news reader using Collage that can retrieve from behind a censorship firewall and show Collage's effectiveness with a live demonstration of its complete infrastructure.
Twittering by cuckoo
Authors: Xu Tianyin , Chen Yang , Fu Xiaoming , Hui Pan
Published: October 2012

Online microblogging services, as exemplified by Twitter, have become immensely popular during the latest years. However, current microblogging systems severely suffer from performance bottlenecks and malicious attacks due to the centralized architecture. As a result, centralized microblogging systems may threaten the scalability, reliability as well as availability of the offered services, not to mention the high operational and maintenance cost.

This demo presents a decentralized, socio-aware microblogging system named Cuckoo. The key aspects of Cuckoo's design is to take advantage of the inherent social relations while leveraging peer-to-peer (P2P) techniques in order to provide scalable, reliable microblogging services. The demo will show these aspects of Cuckoo and provide insights on the performance gain that decentralization and socio-awareness can bring for microblogging systems.
MPAP
Authors: He Yong , Fang Ji , Zhang Jiansong , Shen Haichen , Tan Kun , Zhang Yongguang
Published: October 2012

This demonstration shows a novel virtualization architecture, called
Multi-Purpose Access Point
(MPAP), which can virtualize multiple heterogenous wireless standards based on software radio. The basic idea is to deploy a wide-band radio front-end to receive wireless signals from all wireless standards sharing the same spectrum band, and use separate software base-bands to demodulate information stream for each wireless standard. Based on software radio, MPAP consolidates multiple wireless devices into single hardware platform, and allows them to share the same general-purpose computing resource. Different software base-bands can easily communicate and coordinate with one another. Thus, it also provides better coexistence among heterogenous wireless standards. As an example, we demonstrate to use non-contiguous OFDM in 802.11g PHY to avoid the mutual interference with narrow-band ZigBee communication.
Stratus
Authors: Aggarwal Bhavish , Chitnis Pushkar , Dey Amit , Jain Kamal , Navda Vishnu , Padmanabhan Venkata N. , Ramjee Ramachandran , Schulman Aaron , Spring Neil
Published: October 2012

Cellular radio communication is a significant contributor to battery energy drain on smartphones, in some cases inflating the energy cost by a factor of 5 or more compared to the energy cost of the base device. Stratus is a system to reduce this energy consumption by leveraging cloud resources to make data communication on smartphones more efficient. Using a cloud-based proxy, Stratus employs optimizations that adapt an application's incoming and outgoing traffic to better match the energy characteristics of the radio interface. The optimizations include (a) aggregation to bunch up sporadic transmissions, (b) asymmetric dictionary-based compression to reduce the number of bits transmitted over the air, and (c) opportunistic scheduling to avoid communication during periods of poor signal reception. These optimizations can be used individually, or in combination, subject to an application's delay tolerance. For example, using our Stratus prototype, the aggregation and compression optimizations together achieve up to 50% energy savings for web browsing, while the aggregation and scheduling optimizations together achieve up to 35% energy savings for a media streaming application.
CARMEN
Authors: Bayer Nico , Loziak Krzysztof , Garcia-Saavedra Andres , Sengul Cigdem , Serrano Pablo
Published: October 2012

Even though current mesh networks are mostly WiFi-based, future networks are expected to be highly heterogeneous. Motivated by this expectation, CARMEN (CARrier grade MEsh Networks) project focuses on developing a heterogeneous mesh backhaul to provide carrier-grade (voice, video and data) services. This demo presents resource management and abstraction in CARMEN architecture, which allow meeting the challenges of heterogeneous radio access.
Virtual worlds as cultural models
Authors: Bainbridge William Sims
Published: October 2012

Thirteen gamelike virtual worlds illustrate issues that overlap social science and information science, because they embody rather clear theories of society and culture:
World of Warcraft
,
Lord of the Rings Online
,
Dark Age of Camelot
,
Age of Conan
,
Pirates of the Burning Sea
,
A Tale in the Desert
,
Entropia Universe
,
Anarchy Online
,
The Matrix Online
,
Tabula Rasa
,
EVE Online
,
Star Trek Online, and Dungeons and Dragons Online
. A fourteenth,
Star Wars Galaxies
, illustrates the possibility that not all virtual worlds embody clear theories. After describing the thirteen, this essay discusses their economic systems, social systems, communication challenges, and the ways in which autonomous agents and semi-autonomous secondary avatars enrich interactive complexity.
Structured coalitions in resource selection games
Authors: Feldman Michal , Tennenholtz Moshe
Published: October 2012

We study stability against coalitional deviations in resource selection games where the coalitions have a certain
structure
. In particular, the agents are partitioned into coalitions, and only deviations by the prescribed coalitions are considered. This is in contrast to the classical concept of strong equilibrium according to which any subset of the agents may deviate. In resource selection games, each agent selects a resource from a set of resources, and its payoff is an increasing (or nondecreasing) function of the number of agents selecting its resource. While it has been shown that a strong equilibrium always exists in resource selection games, a closer look reveals severe limitations to the applicability of the existence result even in the simplest case of two identical resources with increasing cost functions. First, these games do not possess a super strong equilibrium in which a fruitful deviation benefits at least one deviator without hurting any other deviator. Second, a strong equilibrium may not exist when the game is played repeatedly. We prove that for any given partition, there exists a super strong equilibrium for resource selection games of identical resources with increasing cost functions. In addition, we show similar existence results for a variety of other classes of resource selection games. For the case of repeated games, we characterize partitions that guarantee the existence of a strong equilibrium. Together, our work introduces a natural concept, which turns out to lead to positive and applicable results in one of the basic domains studied in the literature.
Opinion formation under costly expression
Authors: Wu Fang , Huberman Bernardo A.
Published: October 2012

Opinions play an important role in trust building and the creation of consensus about issues and products and a number of studies have focused on the design, evaluation, and utilization of online opinion systems. However, little effort has been spent on the dynamic aspects of online opinion formation. In this article, we study the dynamics of online opinion expression by analyzing the temporal evolution of vey large sets of user views and determine that in the course of time, later opinions tend to show a big difference with earlier opinions, which moderates the average opinion to the less extreme. Online posters also tend to disagree with previous opinions when the cost of expression is high.
Applying planning to interactive storytelling
Authors: Porteous Julie , Cavazza Marc , Charles Fred
Published: October 2012

We have seen ten years of the application of AI planning to the problem of narrative generation in Interactive Storytelling (IS). In that time planning has emerged as the dominant technology and has featured in a number of prototype systems. Nevertheless key issues remain, such as how best to control the shape of the narrative that is generated (e.g., by using
narrative control knowledge
, i.e., knowledge about narrative features that enhance user experience) and also how best to provide support for real-time interactive performance in order to scale up to more realistic sized systems. Recent progress in planning technology has opened up new avenues for IS and we have developed a novel approach to narrative generation that builds on this. Our approach is to specify narrative control knowledge for a given story world using state trajectory constraints and then to treat these state constraints as
landmarks
and to use them to decompose narrative generation in order to address scalability issues and the goal of real-time performance in larger story domains. This approach to narrative generation is fully implemented in an interactive narrative based on the “Merchant of Venice.” The contribution of the work lies both in our novel use of state constraints to specify narrative control knowledge for interactive storytelling and also our development of an approach to narrative generation that exploits such constraints. In the article we show how the use of state constraints can provide a unified perspective on important problems faced in IS.
Planning interventions in biological networks
Authors: Bryce Daniel , Verdicchio Michael , Kim Seungchan
Published: October 2012

Modeling the dynamics of biological processes has recently become an important research topic in computational biology and systems engineering. One of the most important reasons to model a biological process is to enable high-throughput
in-silico
experiments that attempt to predict or intervene in the process. These experiments can help accelerate the design of therapies through their rapid and inexpensive replication and alteration. While some techniques exist for reasoning with biological processes, few take advantage of the flexible and scalable algorithms popular in AI research. In reasoning about interventions in biological processes, where scalability is crucial for feasible application, we apply AI planning-based search techniques and demonstrate their advantage over existing enumerative methods. We also present a novel formulation of intervention planning that relies on models that characterize and attempt to change the phenotype of a system. We study three biological systems: the yeast cell cycle, a model of the human aging process, and the Wnt5a network governing the metastasis of melanoma in humans. The contribution of our investigation is in demonstrating that: (i) prior approaches, based on dynamic programming, cannot scale as well as heuristic search, and (ii) the newly found scalability enables us to plan previously unknown sequences of interventions that reveal novel and biologically significant responses in the systems which are consistent with biological knowledge in the literature.
A constraint-based approach to scheduling an individual's activities
Authors: Refanidis Ioannis , Yorke-Smith Neil
Published: October 2012

The goal of helping to automate the management of an individual's time is ambitious in terms both of knowledge engineering and of the quality of the plans produced by an AI system. Modeling an individual's activities is itself a challenge, due to the variety of activity, constraint, and preference types involved. Activities might be simple or interruptible; they might have fixed or variable durations, constraints over their temporal domains, and binary constraints between them. Activities might require the individual being at specific locations in order, whereas traveling time should be taken into account. Some activities might require exclusivity, whereas others can be overlapped with compatible concurrent activities. Finally, while scheduled activities generate utility for the individual, extra utility might result from the way activities are scheduled in time, individually and in conjunction.

This article presents a rigorous, expressive model to represent an individual's activities, that is, activities whose scheduling is not contingent on any other person. Joint activities such as meetings are outside our remit; it is expected that these are arranged manually or through negotiation mechanisms and they are considered as fixed busy times in the individual's calendar. The model, formulated as a constraint optimization problem, is general enough to accommodate a variety of situations. We present a scheduler that operates on this rich model, based on the general squeaky wheel optimization framework and enhanced with domain-dependent heuristics and forward checking. Our empirical evaluation demonstrates both the efficiency and the effectiveness of the selected approach. Part of the work described has been implemented in the SelfPlanner system, a Web-based intelligent calendar application that utilizes Google Calendar.
Discovering routines from large-scale human locations using probabilistic topic models
Authors: Farrahi Katayoun , Gatica-Perez Daniel
Published: October 2012

In this work, we discover the daily location-driven routines that are contained in a massive real-life human dataset collected by mobile phones. Our goal is the discovery and analysis of human routines that characterize both individual and group behaviors in terms of location patterns. We develop an unsupervised methodology based on two differing probabilistic topic models and apply them to the daily life of 97 mobile phone users over a 16-month period to achieve these goals. Topic models are probabilistic generative models for documents that identify the latent structure that underlies a set of words. Routines dominating the entire group's activities, identified with a methodology based on the Latent Dirichlet Allocation topic model, include “going to work late”, “going home early”, “working nonstop” and “having no reception (phone off)” at different times over varying time-intervals. We also detect routines which are characteristic of users, with a methodology based on the Author-Topic model. With the routines discovered, and the two methods of characterizing days and users, we can then perform various tasks. We use the routines discovered to determine behavioral patterns of users and groups of users. For example, we can find individuals that display specific daily routines, such as “going to work early” or “turning off the mobile (or having no reception) in the evenings”. We are also able to characterize daily patterns by determining the topic structure of days in addition to determining whether certain routines occur dominantly on weekends or weekdays. Furthermore, the routines discovered can be used to rank users or find subgroups of users who display certain routines. We can also characterize users based on their entropy. We compare our method to one based on clustering using K-means. Finally, we analyze an individual's routines over time to determine regions with high variations, which may correspond to specific events.
Probabilistic models for concurrent chatting activity recognition
Authors: Hsu Jane Yung-Jen , Lian Chia-Chun , Jih Wan-Rong
Published: October 2012

Recognition of chatting activities in social interactions is useful for constructing human social networks. However, the existence of multiple people involved in multiple dialogues presents special challenges. To model the conversational dynamics of concurrent chatting behaviors, this article advocates Factorial Conditional Random Fields (FCRFs) as a model to accommodate co-temporal relationships among multiple activity states. In addition, to avoid the use of inefficient Loopy Belief Propagation (LBP) algorithm, we propose using Iterative Classification Algorithm (ICA) as the inference method for FCRFs. We designed experiments to compare our FCRFs model with two dynamic probabilistic models, Parallel Condition Random Fields (PCRFs) and Hidden Markov Models (HMMs), in learning and decoding based on auditory data. The experimental results show that FCRFs outperform PCRFs and HMMs-like models. We also discover that FCRFs using the ICA inference approach not only improves the recognition accuracy but also takes significantly less time than the LBP inference method.
Performance metrics for activity recognition
Authors: Ward Jamie A. , Lukowicz Paul , Gellersen Hans W.
Published: October 2012

In this article, we introduce and evaluate a comprehensive set of performance metrics and visualisations for continuous activity recognition (AR). We demonstrate how standard evaluation methods, often borrowed from related pattern recognition problems, fail to capture common artefacts found in continuous AR—specifically event fragmentation, event merging and timing offsets. We support our assertion with an analysis on a set of recently published AR papers. Building on an earlier initial work on the topic, we develop a frame-based visualisation and corresponding set of class-skew invariant metrics for the one class versus all evaluation. These are complemented by a new complete set of event-based metrics that allow a quick graphical representation of system performance—showing events that are correct, inserted, deleted, fragmented, merged and those which are both fragmented and merged. We evaluate the utility of our approach through comparison with standard metrics on data from three different published experiments. This shows that where event- and frame-based precision and recall lead to an ambiguous interpretation of results in some cases, the proposed metrics provide a consistently unambiguous explanation.
Inferring colocation and conversation networks from privacy-sensitive audio with implications for computational social science
Authors: Wyatt Danny , Choudhury Tanzeem , Bilmes Jeff , Kitts James A.
Published: October 2012

New technologies have made it possible to collect information about social networks as they are acted and observed
in the wild
, instead of as they are reported in retrospective surveys. These technologies offer opportunities to address many new research questions: How can meaningful information about social interaction be extracted from automatically recorded raw data on human behavior? What can we learn about social networks from such fine-grained behavioral data? And how can all of this be done while protecting privacy? With the goal of addressing these questions, this article presents new methods for inferring colocation and conversation networks from privacy-sensitive audio. These methods are applied in a study of face-to-face interactions among 24 students in a graduate school cohort during an academic year. The resulting analysis shows that networks derived from colocation and conversation inferences are quite different. This distinction can inform future research in computational social science, especially work that only measures colocation or employs colocation data as a proxy for conversation networks.
FolderPredictor
Authors: Bao Xinlong , Dietterich Thomas G.
Published: October 2012

Helping computer users rapidly locate files in their folder hierarchies is a practical research problem involving both intelligent systems and user interface design. This article reports on FolderPredictor, a software system that can reduce the cost of locating files in hierarchical folders. FolderPredictor applies a cost-sensitive prediction algorithm to the user's previous file access information to predict the next folder that will be accessed. Experimental results show that, on average, FolderPredictor reduces the number of clicks spent on locating a file by 50%. Several variations of the cost-sensitive prediction algorithm are discussed. An experimental study shows that the best algorithm among them is a mixture of the most recently used (MRU) folder and the cost-sensitive predictions. Furthermore, FolderPredictor does not require users to adapt to a new interface, but rather meshes with the existing interface for opening files on the Windows platform.