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School of Computer Science Technical Report Series

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    WTF? Locating Performance Problems in Home Networks
    (Georgia Institute of Technology, 2013) Sundaresan, Srikanth ; Grunenberger, Yan ; Feamster, Nick ; Papagiannaki, Dina ; Levin, Dave ; Teixeira, Renata
    Most users of home networks have experienced the intense frustration that comes with diagnosing poor performance. Even determining something as simple as whether a performance problem lies with the ISP or somewhere in the home network is incredibly difficult; this lack of visibility results in unnecessary service calls to ISPs and a general inability to have the network perform as well as it should. In this paper, we design and develop WTF (Where’s The Fault?), a system that reliably determines whether a performance problem lies with the user’s ISP or inside the home network. The tool can also distinguish these problematic situations from the benign case when the network is simply under-utilized. WTF uses cross-layer techniques to discover signatures of various pathologies. We implemented WTF in an off-the-shelf home router; evaluated the techniques in controlled lab experiments under a variety of operating conditions; validated it in real homes where we can directly observe the home conditions and network setup; and deployed it in 30 home networks across North America. The real-world deployment sheds light on common pathologies that occur in home networks. We find, for instance, that many users purchase fast access links but experience significant (and frequent) performance bottlenecks in their home wireless network.
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    Characterizing and Mitigating Web Performance Bottlenecks in Broadband Access Networks
    (Georgia Institute of Technology, 2013) Sundaresan, Srikanth ; Magharei, Nazanin ; Feamster, Nick ; Teixeira, Renata
    We present the first large-scale analysis of Web performance bottlenecks as measured from broadband access networks, using data collected from two extensive home router deployments. We design and implement tools and methods to identify the contribution of critical factors such as DNS lookups and TCP connection establishment to Web page load times and characterize how they contribute to page load times in broadband networks. We find that, as the connection speeds of broadband networks continue to increase, other factors such as TCP connection setup time, server response time, and network latency are often dominant performance bottlenecks. Thus, realizing a “faster Web” requires not only higher download throughput, but also optimizations to reduce both client and server-side latency. We deploy three common caching optimizations inside home networks to reduce latency—content caching, TCP connection caching, and DNS caching—and evaluate their effects on the factors that contribute to page load times in broadband networks.
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    Which Factors Affect Access Network Performance?
    (Georgia Institute of Technology, 2010) Sundaresan, Srikanth ; Feamster, Nick ; Dicioccio, Lucas ; Teixeira, Renata
    This paper presents an analysis of the performance of residential access networks using over four months of round-trip, download, and upload measurements from more than 7,000 users across four ADSL and cable providers in France. Previous studies have characterized residential access network performance, but this paper presents the first study of how access network performance relates to other factors, such as choice of access provider, service-level agreement, and geographic location. We first explore the extent to which user performance matches the capacity advertised by an access provider, and whether the ability to achieve this capacity depends on the user’s access network. We then analyze the extent to which various factors influence the performance that users experience. Finally, we explore how different groups of users experience simultaneous performance anomalies and analyze the common characteristics of users that share fate (e.g., whether users that experience simultaneous performance degradation share the same provider, city). Our analysis informs both users and designers of networked services who wish to improve the reliability and performance of access networks through multihoming and may also assist operators with troubleshooting network issues by narrowing down likely causes.
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    Autonomous Traffic Engineering using Self-Configuring Link Weights
    (Georgia Institute of Technology, 2010) Sundaresan, Srikanth ; Lumezanu, Cristian ; Feamster, Nick ; François, Pierre
    Network operators use traffic engineering to control the flow of traffic across their networks. Existing TE methods establish static topologies offline, either by setting link weights or by configuring paths a priori. These methods require manual configuration and may not be robust in the face of failures. Some methods also require knowledge about traffic demands and may not be able to handle traffic fluctuations. Even when changes in demand are expected, operators must manually tune network configurations to prepare for them. Because adjusting configurations is difficult to get right, we start from an extreme design point, asking instead whether it is possible to perform traffic engineering online without having to perform any a priori configuration. Our traffic engineering technique, SculpTE, adapts to changing traffic demands by automatically configuring link weights in a stable manner. SculpTE balances load across the network by continually adjusting link weights to expose lightly-loaded paths. We evaluate SculpTE using a simple analytical model and simulations on realistic ISP network topologies. Our results show that SculpTE achieves excellent load balancing, responsiveness, and stability compared to state-of-the-art TE schemes, without requiring network operators to perform any offline configuration.
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    Towards an Internet Connectivity Market
    (Georgia Institute of Technology, 2009) Feamster, Nick ; Hassan, Umayr ; Sundaresan, Srikanth ; Valancius, Vytautas ; Johari, Ramesh ; Vazirani, Vijay V.
    Today’s Internet achieves end-to-end connectivity through bilateral contracts between neighboring networks; unfortunately, this “one size fits all” connectivity results in less efficient paths, unsold capacity and unmet demand, and sometimes catastrophic market failures that result in global disconnectivity. This paper presents the design and evaluation of MINT, a Market for Internet Transit. MINT is a connectivity market and corresponding set of protocols that allows ISPs to offer path segments on an open market. Edge networks bid for end-to-end paths, and a mediator matches bids for paths to collections of path segments that form end-to-end paths. MINT can be deployed using protocols that are present in today’s routers, and it operates in parallel with the existing routing infrastructure and connectivity market. We present MINT’s market model and protocol design; evaluate how MINT improves efficiency, the utility of edge networks, and the profits of transit networks; and how MINT can operate at Internet scale.