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Search Results: 1 - 10 of 6169 matches for " Jennifer Rexford "
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Neighbor-Specific BGP: More Flexible Routing Policies While Improving Global Stability
Yi Wang,Michael Schapira,Jennifer Rexford
Computer Science , 2009,
Abstract: Please Note: This document was written to summarize and facilitate discussion regarding (1) the benefits of changing the way BGP selects routes to selecting the most preferred route allowed by export policies, or more generally, to selecting BGP routes on a per-neighbor basis, (2) the safety condition that guarantees global routing stability under the Neighbor-Specific BGP model, and (3) ways of deploying this model in practice. A paper presenting the formal model and proof of the stability conditions was published at SIGMETRICS 2009 and is available online.
Nation-State Routing: Censorship, Wiretapping, and BGP
Josh Karlin,Stephanie Forrest,Jennifer Rexford
Computer Science , 2009,
Abstract: The treatment of Internet traffic is increasingly affected by national policies that require the ISPs in a country to adopt common protocols or practices. Examples include government enforced censorship, wiretapping, and protocol deployment mandates for IPv6 and DNSSEC. If an entire nation's worth of ISPs apply common policies to Internet traffic, the global implications could be significant. For instance, how many countries rely on China or Great Britain (known traffic censors) to transit their traffic? These kinds of questions are surprisingly difficult to answer, as they require combining information collected at the prefix, Autonomous System, and country level, and grappling with incomplete knowledge about the AS-level topology and routing policies. In this paper we develop the first framework for country-level routing analysis, which allows us to answer questions about the influence of each country on the flow of international traffic. Our results show that some countries known for their national policies, such as Iran and China, have relatively little effect on interdomain routing, while three countries (the United States, Great Britain, and Germany) are central to international reachability, and their policies thus have huge potential impact.
SoftCell: Taking Control of Cellular Core Networks
Xin Jin,Li Erran Li,Laurent Vanbever,Jennifer Rexford
Computer Science , 2013,
Abstract: Existing cellular networks suffer from inflexible and expensive equipment, and complex control-plane protocols. To address these challenges, we present SoftCell, a scalable architecture for supporting fine-grained policies for mobile devices in cellular core networks. The SoftCell controller realizes high-level service polices by directing traffic over paths that traverse a sequence of middleboxes, optimized to the network conditions and user locations. To ensure scalability, the core switches forward traffic on hierarchical addresses (grouped by base station) and policy tags (identifying paths through middleboxes). This minimizes data-plane state in the core switches, and pushes all fine-grained state to software switches at the base stations. These access switches apply fine-grained rules, specified by the controller, to map all traffic to the appropriate addresses and tags. SoftCell guarantees that packets in the same connection traverse the same sequence of middleboxes in both directions, even in the presence of mobility. Our characterization of real LTE workloads, micro-benchmarks on our prototype controller, and large-scale simulations demonstrate that SoftCell improves the flexibility of cellular core networks, while enabling the use of inexpensive commodity switches and middleboxes.
SNAP: Stateful Network-Wide Abstractions for Packet Processing
Mina Tahmasbi Arashloo,Yaron Koral,Michael Greenberg,Jennifer Rexford,David Walker
Computer Science , 2015,
Abstract: Early programming languages for Software-Defined Networking (SDN) were built on top of the simple match-action paradigm offered by OpenFlow 1.0. However, emerging switches and middleboxes offer much more sophisticated support for persistent state in the data plane, without involving a central controller. In this paper, we introduce high-level programming abstractions and compiler technology that exploit these low-level mechanisms. Our SNAP language allows programmers to mix stateful programming with pure packet processing using global, persistent arrays indexed by packet-header fields. This allows SNAP programs to learn about the network environment, store per-flow information, and implement various stateful network functions. SNAP is high-level and modular, allowing flexible composition of independently-written programs on top of a "one-big-switch" abstraction. Our SNAP compiler analyzes programs to discover dependencies and race conditions, and offers a simple network transaction abstraction as a way to resolve the latter. A mixed integer-linear program optimizes both placement of state variables on switches and also routing traffic through them efficiently and in the right order. To compile programs efficiently, our compiler uses a novel variant of binary decision diagrams (BDDs), extended to incorporate stateful components. We have implemented a prototype compiler, applied it to a range of programs and topologies, and measured our techniques' scalability.
A Provably-Correct Protocol for Seamless Communication with Mobile, Multi-Homed Hosts
Matvey Arye,Erik Nordstrom,Robert Kiefer,Jennifer Rexford,Michael J. Freedman
Computer Science , 2012,
Abstract: Modern consumer devices, like smartphones and tablets, have multiple interfaces (e.g., WiFi and 3G) that attach to new access points as users move. These mobile, multi-homed computers are a poor match with an Internet architecture that binds connections to fixed end-points with topology- dependent addresses. As a result, hosts typically cannot spread a connection over multiple interfaces or paths, or change locations without breaking existing connections. In this paper, we introduce ECCP, an end-host connection control protocol that allows hosts to communicate over mul- tiple interfaces with dynamically-changing IP addresses. Each ECCP connection consists of one or more flows, each associated with an interface or path. A host can move an existing flow from one interface to another or change the IP address using in-band signaling, without any support from the underlying network. We use formal models to verify that ECCP works correctly in the presence of packet loss, out-of-order delivery, and frequent mobility, and to identify bugs and design limitations in earlier mobility protocols.
RAPTOR: Routing Attacks on Privacy in Tor
Yixin Sun,Anne Edmundson,Laurent Vanbever,Oscar Li,Jennifer Rexford,Mung Chiang,Prateek Mittal
Computer Science , 2015,
Abstract: The Tor network is a widely used system for anonymous communication. However, Tor is known to be vulnerable to attackers who can observe traffic at both ends of the communication path. In this paper, we show that prior attacks are just the tip of the iceberg. We present a suite of new attacks, called Raptor, that can be launched by Autonomous Systems (ASes) to compromise user anonymity. First, AS-level adversaries can exploit the asymmetric nature of Internet routing to increase the chance of observing at least one direction of user traffic at both ends of the communication. Second, AS-level adversaries can exploit natural churn in Internet routing to lie on the BGP paths for more users over time. Third, strategic adversaries can manipulate Internet routing via BGP hijacks (to discover the users using specific Tor guard nodes) and interceptions (to perform traffic analysis). We demonstrate the feasibility of Raptor attacks by analyzing historical BGP data and Traceroute data as well as performing real-world attacks on the live Tor network, while ensuring that we do not harm real users. In addition, we outline the design of two monitoring frameworks to counter these attacks: BGP monitoring to detect control-plane attacks, and Traceroute monitoring to detect data-plane anomalies. Overall, our work motivates the design of anonymity systems that are aware of the dynamics of Internet routing.
Corporate Profit Growth and Variability in US Unemployment Rate
Rexford Abaidoo
International Journal of Economics and Finance , 2012, DOI: 10.5539/ijef.v4n7p3
Abstract: This study investigates effects of corporate profit growth, macroeconomic uncertainty and other key economic indicators on the potential for lower unemployment condition in the US economy. Using marginal effect probit estimates, this study finds that, sustained growth in corporate profit and appreciable economic growth (as measured by GDP growth) are significant in determining the likelihood of achieving lower unemployment rate. Overall results however, show that among variables tested, reduction in perceived macroeconomic uncertainty is the dominant variable with the potential to significantly impact the likelihood of having lower unemployment rate.
Macroeconomic Volatility and Macroeconomic Indicators among Sub-Saharan African Economies
Rexford Abaidoo
International Journal of Economics and Finance , 2012, DOI: 10.5539/ijef.v4n10p1
Abstract: This study explored how disaggregated macroeconomic volatility parameters impact key macroeconomic indicators in Sub-Saharan Africa. The study employed a number of external and regional macroeconomic volatility parameters derived from macroeconomic data sourced from the IMF in its empirical analysis. Dynamic Panel fixed effect model employed show that regional macroeconomic volatility parameters tend to have more statistically significant impact (positive and negative) on performance indicators in the sub-region than external macroeconomic volatility parameters. This study also finds that among regional macroeconomic volatility parameters shaping growth conditions in the sub-region, investment growth volatility is the dominant condition with statistically significant impact on key macroeconomic indicators in the sub-region. Results further point to evidence of significant moderating effects in how external and regional macroeconomic volatility parameters impact regional macroeconomic indicators.
Economic Growth, Regional Savings and FDI in Sub-Saharan Africa: Trivariate Causality and Error Correction Modeling Approach
Rexford Abaidoo
International Journal of Economics and Finance , 2012, DOI: 10.5539/ijef.v4n11p40
Abstract: Empirical studies examining the dynamic causal relationship between key macroeconomic variables using varied forms of bivariate causality methodology abound in the macroeconomic and finance literature. Causal inference based on such bivariate causality approach however, has been criticized for its inherent likelihood to draw causal inference or attribute causation to variables in scenarios where an omitted variable might have a better claim; Lutkephol (1982), Umberto Triacca (1998). This study is modeled to reduce this inherent weakness by employing trivariate causality methodology through error correction approach. Using aggregate data on Sub-Sahara Africa spanning the period 1977 to 2010, this study finds joint uni-directional causal relationship running from FDI and Gross Regional Savings growth to regional GDP growth. Empirical results further document additional uni-directional joint causal relationship stemming from GDP growth and Gross Regional Savings to growth in FDI inflow into the sub-region.
Akt Deficiency Attenuates Muscle Size and Function but Not the Response to ActRIIB Inhibition
Marcus D. Goncalves,Emidio E. Pistilli,Anthony Balduzzi,Morris J. Birnbaum,Jennifer Lachey,Tejvir S. Khurana,Rexford S. Ahima
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012707
Abstract: Akt is a critical mediator of developmental skeletal muscle growth. Treatment with a soluble ActRIIB fusion protein (ActRIIB-mFc) increases skeletal muscle mass and strength by inhibiting myostatin and related peptides. Recent in vitro studies have suggested that Akt signaling is necessary for the ability of ActRIIB inhibition to induce muscle hypertrophy. Thus, we hypothesized that mice deficient in either Akt1 or Akt2 would not respond to in vivo inhibition of ActRIIB with ActRIIB-mFc treatment.
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