The emergence of large cloud providers in the last decade has transformed the Internet, resulting in a seemingly ever-growing set of datacenters, points of presence, and network peers. Despite the availability of closer peering locations, some networks continue to peer with cloud providers at distant locations, traveling thousands of kilometers. In this paper, we employ a novel cloud-based traceroute campaign to characterize the distances networks travel to peer with the cloud. This unique approach allows us to gain unprecedented insights into the peering patterns of networks. Our findings reveal that 50% of the networks peer within 300 kilometers of the nearest datacenter. However, our analysis also reveals that over 20% of networks travel at least 6,700 kilometers beyond the proximity of the nearest computing facility, and some as much as 18,791 kilometers! While these networks connect with the cloud worldwide, from South America to Europe and Asia, many come to peer with cloud providers in North America, even from Oceania and Asia. We explore possible motivations for the persistence of distant peering, discussing factors such as cost-effective routes, enhanced peering opportunities, and access to exclusive content.

In this paper, we study the viability of LEO networks as a failover network. We contextualize our analysis by framing the capacity of satellite networks relative to lost capacity due to submarine cable failure. Specifically, we focus on scenarios where LEO networks act as failovers for submarine cables, providing a concrete target capacity to be fulfilled by the satellite network. We introduce a new model and simulator that help us estimate the failover capacity. We identify key factors determining the actual capacity available on the satellite network: the total area of the country, the terminal distribution policy used by the government, the spectrum allocation and traffic engineering policies used by the LEO network operator. Based on our findings, we make policy recommendations to governments that can result in an increase of up to 1.8× in the failover capacity without requiring additional infrastructure. However, we find after implementing all our recommendations, with 200k terminals deployed and no competing traffic in the network, a satellite network can only satisfy 0.9-14.7% of the capacity lost due to submarine cable failure in four out of six case studies.

We introduce Borges (Better ORGanizations Entities mappingS), a novel framework for improving AS-to-Organization mappings using Large Language Models (LLMs). Existing approaches, such as AS2Org and its extensions, rely on static WHOIS data and rule-based extraction from PeeringDB records, limiting their ability to capture complex, dynamic organizational structures. Borges overcomes these limitations by combining traditional sources with few-shot LLM prompting to extract sibling relationships from free-text fields in PeeringDB, and by introducing website-based inference using redirect chains, domain similarity, and favicon analysis. Our evaluation shows that Borges outperforms prior methods, achieving a 7% improvement in sibling ASN identification and an Organization Factor score of 0.3576. It also expands the recognized user base of large Internet conglomerates by 192 million users (≈ 5% of the global Internet population) and improves geographic footprint estimates across multiple regions.

The Internet's connectivity relies on a fragile submarine cable network (SCN), yet existing tools fall short in assessing its criticality. We introduce Calypso, a new framework that leverages traceroute data to map traffic to submarine cables. Validated through real-world case studies, Calypso reveals hidden risks and offers new insights to enhancing SCN resilience.

In just a few decades, the Internet has evolved from a research prototype to a cyber-physical infrastructure of critical importance for modern society and the global economy. Surprisingly, despite its new role, the survivability of the Internet-its ability to fulfill its mission in the presence of large-scale failures-has received limited attention. We introduce Domino, our initial design and implementation of a testbench tool for stress testing the Internet's routing system, a key element of the critical Internet infrastructure. The simulation-based testbench consists of a comprehensive and flexible framework that allows for the incorporation of diverse survivability metrics, provides a platform for specifying, evaluating, and comparing different topologies of the underlying Internet infrastructure, and can account for modifications to networking protocols and architectural components. By demonstrating the utility of the proposed testbench with a number of illustrative examples, we make a case for stress testing as a viable approach to evaluating the Internet's survivability in the face of evolving challenges.

This paper presents the first large-scale empirical study of commercial personally identifiable information (PII) removal systems --- commercial services that claim to improve privacy by automating the removal of PII from data broker's databases. Popular examples of such services include DeleteMe, Mozilla Monitor, Incogni, among many others. The claims these services make may be very appealing to privacy-conscious Web users, but how effective these services actually are at improving privacy has not been investigated. This work aims to improve our understanding of commercial PII removal services in multiple ways. First, we conduct a user study where participants purchase subscriptions from four popular PII removal services, and report (i) what PII the service find, (ii) from which data brokers, (iii) whether the service is able to have the information removed, and (iv) whether the identified information actually is PII describing the participant. And second, by comparing the claims and promises the services makes (e.g. which and how many data brokers each service claims to cover). We find that these services have significant accuracy and coverage issues that limit the usefulness of these services as a privacy-enhancing technology. For example, we find that the measured services are unable to remove the majority of the identified PII records from data broker's (48.2% of the successfully removed found records) and that most records identified by these services are not PII about the user (study participants found that only 41.1% of records identified by these services were PII about themselves).

The mobile telecommunication industry is undergoing continuous evolution to cope with ever increasing service requirements and expectations of end users. This has recently led to the rise of Mobile Network Aggregators (MNAs), a new type of global virtual operators that deliver mobile communication services by utilizing multiple Mobile Network Operators (MNOs), dynamically connecting to the one that best meets their customers’ needs based on location and time. MNAs can then offer optimized global coverage by connecting to local MNOs that have limited (e.g., national) geographic service. In this paper, we provide a first in-depth analysis of the operations of three major MNAs: Google Fi, Twilio, and Truphone. We conduct performance measurements across these MNAs for critical applications spanning DNS, web browsing, and video streaming, and compare their performance against that of a traditional MNO from two very diverse geographical locations, US and Spain. We find that MNAs may introduce some delay compared to local MNOs in the region where the user is roaming, yet they offer significant performance improvements over the traditional MNOs roaming model, such as home-routed roaming. To fully assess the potential benefits of the MNA model, we also carry out emulation studies assessing the potential performance gains that MNAs could achieve by deploying both control and user plane functions of open-source 5G implementations across different Amazon Web Services locations.

In just a few decades, the Internet has evolved from a research prototype to a critical infrastructure for modern society and the global economy. Despite its importance, the Internet's survivability amid large-scale failures has received limited attention. We present a testbench design for stress testing the Internet's routing system. This simulation-based framework allows for flexible integration of survivability metrics, evaluation of different topologies, and assessment of protocol and architectural changes. With several illustrative examples, we show the effectiveness of our proposed testbench and make a case for stress testing as a viable approach to evaluating the survivability of inter-domain routing against evolving challenges.

We present the first large-scale analysis of the adoption of third-party serving infrastructures in government digital services. Drawing from data collected across 61 countries spanning every continent and region, capturing over 82% of the world's Internet population, we examine the preferred hosting models for public-facing government sites and associated resources. Leveraging this dataset, we analyze government hosting strategies, cross-border dependencies, and the level of centralization in government web services. Among other findings, we show that governments predominantly rely on third-party infrastructure for data delivery, although this varies significantly, with even neighboring countries showing contrasting patterns. Despite a preference for third-party hosting solutions, most government URLs in our study are served from domestic servers, although again with significant regional variation. Looking at overseas located servers, while the majority are found in North America and Western Europe, we note some interesting bilateral relationships (e.g., with 79% of Mexico's government URLs being served from the US, and 26% of China's government URLs from Japan). This research contributes to understanding the evolving landscape of serving infrastructures in the government sector, and the choices governments make between leveraging third-party solutions and maintaining control over users' access to their services and information.

The Venezuelan crisis, unfolding over the past decade, has garnered international attention due to its impact on various sectors of civil society. While studies have extensively covered the crisis's effects on public health, energy, and water management, this paper delves into a previously unexplored area - the impact on Venezuela's Internet infrastructure. Amidst Venezuela's multifaceted challenges, understanding the repercussions of this critical aspect of modern society becomes imperative for the country's recovery.

We report on a large-scale study of the complex client-side DNS infrastructure. Using all RIPE Atlas probes and our crowdsourced experiment, we capture clients' ingress and egress DNS resolvers from 880 ISPs in 113 different countries, around the world. We study different aspects of this mismatch - including the distance between clients and ingress/egress resolvers and cases of country-level mismatch between clients and their resolvers.

A new model of global virtual Mobile Network Operator (MNO) - the Mobile Network Aggregator (MNA) - has recently been gaining significant traction. MNAs provide mobile communications services to their customers by leveraging multiple MNOs, and connecting through the one that best match their customers' needs at any point in time (and space). MNAs naturally provide optimized global coverage by connecting through local MNOs across the different geographic regions they provide service. In this paper, we dissect the operations of three MNAs, namely, Google Fi, Twilio and Truphone. We perform measurements using the three selected MNAs to assess their performance for three major applications, namely, DNS, web browsing and video streaming. We benchmark their performance comparing it to the one of a traditional MNO. We find that even MNAs provide some delay penalty compared to the service accessed through the local MNOs in the geographic area where the user is roaming, they can significantly improve performance compared to traditional roaming model of the MNOs (e.g. home routed roaming). Finally, in order to fully quantify the potential benefits that can be realized using the MNA model, we perform a set of emulations by deploying both control and user plane functions of open-source 5G implementations in different locations of AWS, and measure the potential gains.

While non-pharmaceutical interventions (NPIs) such as stay-at-home, shelter-in-place, and school closures are considered the most effective ways to limit the spread of infectious diseases, their use is generally controversial given the political, ethical, and socioeconomic issues they raise. Part of the challenge is the non-obvious link between the level of compliance with such measures and their effectiveness.

IP Exchange Providers (IPX-Ps) offer to their customers (e.g., mobile or IoT service providers) global data roaming and support for a variety of emerging services. They peer to other IPX-Ps and form the IPX network, which interconnects 800 MNOs worldwide offering their customers access to mobile services in any other country. Despite the importance of IPX-Ps, little is known about their operations and performance. In this paper, we shed light on these opaque providers by analyzing a large IPX-P with more than 100 PoPs in 40+ countries, with a particularly strong presence in America and Europe. Specifically, we characterize the traffic and performance of the main infrastructures of the IPX-P (i.e., 2-3-4G signaling and GTP tunneling), and provide implications for its operation, as well as for the IPX-P's customers. Our analysis is based on statistics we collected during two time periods (i.e., prior and during COVID-19 pandemic) and includes insights on the main service the platform supports (i.e., IoT and data roaming), traffic breakdown and geographical/temporal distribution, communication performance (e.g., tunnel setup time, RTTs). Our results constitute a step towards advancing the understanding of IPX-Ps at their core, and provide guidelines for their operations and customer satisfaction.

The last three decades have seen much evolution in web and network protocols: amongst them, a transition from HTTP/1.1 to HTTP/2 and a shift from loss-based to delay-based TCP congestion control algorithms. This paper argues that these two trends come at odds with one another, ultimately hurting web performance. Using a controlled synthetic study, we show how delay-based congestion control protocols (e.g., BBR and CUBIC + Hybrid Slow Start) result in the underestimation of the available congestion window in mobile networks, and how that dramatically hampers the effectiveness of HTTP/2. To quantify the impact of such finding in the current web, we evolve the web performance toolbox in two ways. First, we develop Igor, a client-side TCP congestion control detection tool that can differentiate between loss-based and delay-based algorithms by focusing on their behavior during slow start. Second, we develop a Chromium patch which allows fine-grained control on the HTTP version to be used per domain. Using these new web performance tools, we analyze over 300 real websites and find that 67% of sites relying solely on delay-based congestion control algorithms have better performance with HTTP/1.1.

Nearly all international data is carried by a mesh of submarine cables connecting virtually every region in the world. It is generally assumed that Internet services rely on this submarine cable network (SCN) for backend traffic, but that most users do not directly depend on it, as popular resources are either local or cached nearby. In this paper, we study the criticality of the SCN from the perspective of end users. We present a general methodology for analyzing the reliance on the SCN for a given region, and apply it to the most popular web resources accessed by users in 63 countries from every inhabited continent, collectively capturing ≈80% of the global Internet population. We find that as many as 64.33% of all web resources accessed from a specific country rely on the SCN. Despite the explosive growth of data center and CDN infrastructure around the world, at least 28.22% of the CDN-hosted resources traverse a submarine cable.

Support for "things" roaming internationally has become critical for Internet of Things (IoT) verticals, from connected cars to smart meters and wearables, and explains the commercial success of Machine-to-Machine (M2M) platforms. We analyze IoT verticals operating with connectivity via IoT SIMs, and present the first large-scale study of commercially deployed IoT SIMs for energy meters. We also present the first characterization of an operational M2M platform and the first analysis of the rather opaque associated ecosystem.

After three highly successful editions of the Internet-QoE workshop organized at ACM SIGCOMM 2016, ACM SIGCOMM 2017, and IEEE ICDCS 2018, the goal of the fourth edition of the Internet-QoE workshop is to scale the concepts of Quality of Experience (user satisfaction, user engagement, and behavioral analysis) out of the lab studies context and bring it to the analysis and operation of distributed systems and communication networks, giving a user-centric perspective to the research performed by the MOBICOM community. By fostering an explicit and deep integration of the end-user directly into the design, analysis and management of large-scale operational networks, we expect to reduce the gap between QoE research and its application to future network management paradigms, as well as to provide a more targeted end-user perspective to the research on distributed communication systems. The 4th edition of Internet-QoE also focuses on novel end-user services enabled by next generation technologies such as immersive media (3D, Virtual Reality and Augmented Reality), self-driving cars, intelligent manufacturing systems, Industry 4.0 and tactile Internet, 5G ultra-low-latency mobile networks, and real-time applications.

The rapid growth in the number of mobile devices, subscriptions and their associated traffic, has served as motivation for several projects focused on improving mobile users' quality of experience (QoE). Few have been as contentious as the Google-initiated Accelerated Mobile Project (AMP), both praised for its seemingly instant mobile web experience and criticized based on concerns about the enforcement of its formats. This paper presents the first characterization of AMP's impact on users' QoE. We do this using a corpus of over 2,100 AMP webpages, and their corresponding non-AMP counterparts, based on trendy-keyword-based searches. We characterized AMP's impact looking at common web QoE metrics, including Page Load Time, Time to First Byte and SpeedIndex (SI). Our results show that AMP significantly improves SI, yielding on average a 60% lower SI than non-AMP pages without accounting for prefetching. Prefetching of AMP pages pushes this advantage even further, with prefetched pages loading over 2,000ms faster than non-prefetched AMP pages. This clear boost may come, however, at a non-negligible cost for users with limited data plans as it incurs an average of over 1.4~MB of additional data downloaded, unbeknownst to users.

There has been a growing interest in measuring and optimizing the power efficiency of mobile apps. Traditional power evaluations rely either on inaccurate software-based solutions or on ad-hoc testbeds composed of a power meter and a mobile device. This demonstration presents BatteryLab, our solution to share existing battery testing setups to build a distributed platform for battery measurements. Our vision is to transform independent battery testing setups into vantage points of a planetary-scale measurement platform offering heterogeneous devices and testing conditions. We demonstrate BatteryLab functionalities by investigating the energy efficiency of popular websites when loaded via both Android and iOS browsers. Our demonstration is also live at https://batterylab.dev/.

The growth of global Internet traffic has driven an exponential expansion of the submarine cable network, both in terms of the sheer number of links and its total capacity. Today, a complex mesh of hundreds of cables, stretching over 1 million kilometers, connects nearly every corner of the earth and is instrumental in closing the remaining connectivity gaps. Despite the scale and critical role of the submarine network for both business and society at large, our community has mostly ignored it, treating it as a black box in most Internet studies, from connectivity to inter-domain traffic and reliability. We make the case for a new research agenda focused on characterizing the global submarine network and the critical role it plays as a basic component of any inter-continental end-to-end connection.

In-Flight Communication (IFC), available on a growing number of commercial flights, is often received by consumers with both awe for its mere availability and harsh criticism for its poor performance. Indeed, IFC provides Internet connectivity in some of the most challenging conditions with aircraft traveling at speeds in excess of 500 mph at 30,000 feet above the ground. Yet, while existing services do provide basic Internet \em accessibility, anecdotal reports rank their quality of service as, at best, poor. In this paper, we present the first characterization of deployed IFC systems. Using over 45 flight-hours of measurements, we profile the performance of IFC across the two dominant access technologies -- direct air-to-ground communication (DA2GC) and mobile satellite service (MSS). We show that IFC QoS is in large part determined by the high latencies inherent to DA2GC and MSS, with RTTs averaging 200ms and 750ms, respectively, and that these high latencies directly impact the performance of common applications such as web browsing. While each IFC technology is based on well studied wireless communication technologies, our findings reveal that IFC links experience further degraded link performance than their technological antecedents. We find median loss rates of 7%, and nearly 40% loss at the 90th percentile for MSS, 6.8x larger than recent characterizations of residential satellite networks. We extend our IFC study exploring the potential of the newly released HTTP/2 and QUIC protocols in an emulated IFC environment, finding that QUIC is able to improve page load times by as much as 7.9 times. In addition, we find that HTTP/2»s use of multiplexing multiple requests onto a single TCP connection performs up to 4.8x \em worse than HTTP/1.1 when faced with large numbers of objects. We use network emulation to explore proposed technological improvements to existing IFC systems finding that high link losses, and not bandwidth, account for the largest factor of performance degradation with applications such as web browsing.

The impressive growth of the mobile Internet has motivated several industry reports retelling the story in terms of number of devices or subscriptions sold per regions, or the increase in mobile traffic, both WiFi and cellular. Yet, despite the abundance of such reports, we still lack an understanding of the impact of cellular networks around the world.

The goal of our work is to characterize the current state of Cuba's access to the wider Internet. This work is motivated by recent improvements in connectivity to the island and the growing commercial interest following the ease of restrictions on travel and trade with the US. In this paper, we profile Cuba's networks, their connections to the rest of the world, and the routes of international traffic going to and from the island. Despite the addition of the ALBA-1 submarine cable, we find that round trip times to websites hosted off the island remain very high; pings to popular websites frequently took over 300 ms. We also find a high degree of path asymmetry in traffic to/from Cuba. Specifically, in our analysis we find that traffic going out of Cuba typically travels through the ALBA-1 cable, but, surprisingly, traffic on the reverse path often traverses high-latency satellite links, adding over 200 ms to round trip times. Last, we analyze queries to public DNS servers and SSL certificate requests to characterize the availability of network services in Cuba.

Crowdsensing leverages the pervasiveness and power of mobile devices, such as smartphones and tablets, to enable ordinary citizens to collect, transport and verify data. Application domains range from environment monitoring, to infrastructure management and social computing. Crowdsensing services' effectiveness is a direct result of their coverage, which is driven by the recruitment and mobility patterns of participants. Due to the typically uneven population distributions of most areas, and the regular mobility patterns of participants, less popular or populated areas suffer from poor coverage. In this paper, we present Crowd Soft Control (CSC), an approach to exert limited control over the actions of participants by leveraging the built-in incentives of location-based gaming and social applications. By pairing crowdsensing with location-based applications, CSC allows sensing services to reuse the incentives of location-based apps to steer the actions of participating users and increase the effectiveness of sensing campaigns. While there are several domains where this intentional movement is useful such as data muling, this paper presents the design, implementation and evaluation of CSC applied to crowdsensing. We built a prototype of CSC and integrated it with two location-based applications, and crowdsensing services. Our experimental results demonstrate the low-cost of integration and minimal overhead of CSC.

Poor visibility into the network hampers progress in a number of important research areas, from network troubleshooting to Internet topology and performance mapping. This persistent, well-known problem has served as motivation for numerous proposals to build or extend existing Internet measurement platforms by recruiting larger, more diverse vantage points. Capturing the edge of the network, however, remains an elusive goal. We argue that at its root the problem is one of incentives. Today's measurement platforms build on the assumption that the goals of experimenters and those hosting the platform are the same. As much of the Internet growth occurs in residential broadband networks, this assumption no longer holds. We present a measurement experimentation platform that reaches the network edge by explicitly aligning the objectives of the experimenters with those of the users hosting the platform. Dasu-our current prototype-is designed to support both network measurement experimentation and broadband characterization. Dasu has been publicly available since July 2010 and has been installed by over 100 000 users with a heterogeneous set of connections spreading across 2431 autonomous systems (ASs) and 166 countries. We discuss some of the challenges we faced building and using a platform for the Internet's edge, describe its design and implementation, and illustrate the unique perspective its current deployment brings to Internet measurement.

Though the impact of file-sharing of copyrighted content has been discussed for over a decade, only in the past few years have countries begun to adopt legislation to criminalize this behavior. These laws impose penalties ranging from warnings and monetary fines to disconnecting Internet service. While their supporters are quick to point out trends showing the efficacy of these laws at reducing use of file-sharing sites, their analyses rely on brief snapshots of activity that cannot reveal long- and short-term trends.

We present the first study of broadband services in their broader context, evaluating the impact of service characteristics (such as capacity, latency and loss), their broadband pricing and user demand. We explore these relationships, beyond correlation, with the application of natural experiments. Most efforts on broadband service characterization have so far focused on performance and availability, yet we lack a clear understanding of how such services are being utilized and how their use is impacted by the particulars of the market. By analyzing over 23-months of data collected from 53,000 end hosts and residential gateways in 160 countries, along with a global survey of retail broadband plans, we empirically study the relationship between broadband service characteristics, pricing and demand. We show a strong correlation between capacity and demand, even though subscribers rarely fully utilize their links, but note a law of diminishing returns with relatively smaller increases in demand at higher capacities. Despite the fourfold increase in global IP traffic, we find that user demand on the network over a three year period remained constant for a given bandwidth capacity. We exploit natural experiments to examine the causality between these factors. The reported findings represent an important step towards understanding how user behavior, and the market features that shape it, affect broadband networks and the Internet at large.

DNS plays a critical role in the performance of smartdevices within cellular networks. Besides name resolution, DNS is commonly relied upon for directing users to nearby content caches for better performance. In light of this, it is surprising how little is known about the structure of cellular DNS and its effectiveness as a client localization method.

Characterizing the flow of Internet traffic is important in a wide range of contexts, from network engineering and application design to understanding the network impact of consumer demand and business relationships. Despite the growing interest, the nearly impossible task of collecting large-scale, Internet-wide traffic data has severely constrained the focus of traffic-related studies.

When a new technology reaches the market, we typically focus on the want or need that it can fulfill. As the technology becomes a commodity and its market matures, reliability often become a key differentiating factor between competing products. We posit that as broadband capacities continue to improve and users migrate to over-the-Internet services, such as on-demand video and voice-over-IP services, we will see this common pattern emerge for broadband services. In this poster, we present the first study of reliability in broadband networks. Using data collected from residential gateways (via FCC/SamKnows), we study the availability and reliability of fixed-line broadband services across the US. Using natural experiments, we look at the impact of increased network downtime on user network demand. We use traditional metrics (e.g. failure rate, MTBF, MTTR) to quantify broadband services, as well as each ISP's configured DNS. Since the impact of a network outage will depend on when it occurred (e.g. time of day), we compare ISP services by the annual average number of bytes lost, based on typical user demand during periods of network downtime.

A social news site presents user-curated content, ranked by popularity. Popular curators like Reddit, or Facebook have become effective way of crowdsourcing news or sharing for personal opinions. Traditionally, these services require a centralized authority to aggregate data and determine what to display. However, the trust issues that arise from a centralized system are particularly damaging to the "Web democracy" that social news sites are meant to provide. In this poster, we present cliq, a decentralized social news curator. cliq is a P2P based social news curator that provides private and unbiased reporting. All users in cliq share responsibility for tracking and providing popular content. Any user data that cliq needs to store is also managed across the network. We first inform our design of cliq through an analysis of Reddit. We design a way to provide content curation without a persistent moderator, or usernames.

No abstract available.

An accurate Internet topology graph is important in many areas of networking, from understanding ISP business relationships to diagnosing network anomalies. Most Internet mapping efforts have derived the network structure, at the level of interconnected autonomous systems (ASes), from a rather limited set of vantage points. In this paper, we argue that a promising approach to revealing the hidden areas of the Internet topology is through active measurement from an observation platform that scales with the growing Internet. By leveraging measurements performed by an extension to a popular P2P system, we show that this approach indeed exposes significant new topological information. Our study is based on traceroute measurements from more than 992,000 IPs in over 3,700 ASes distributed across the Internet hierarchy, many in regions of the Internet not covered by publicly available path information. To address this issue we develop heuristics that identify 23,914 new AS links not visible in the publicly-available BGP data-12.86 percent more customer-provider links and 40.99 percent more peering links, than previously reported. We validate our heuristics using data from a tier-1 ISP, and show that they successfully filter out all false links introduced by public IP-to-AS mapping. We analyze properties of the Internet graph that includes these new links and characterize why they are missing. Finally, we have made the identified set of links and their inferred relationships publicly available.

People use P2P systems such as BitTorrent to share an unprecedented variety and amount of content with others around the world. The random connection pattern used by BitTorrent has been shown to result in reduced performance for users and costly cross-ISP traffic. Although several client-side systems have been proposed to improve the locality of BitTorrent traffic, their effectiveness is limited by the availability of local peers. We show that sufficient locality is present in swarms - if one looks at the right time. We find that 50% of ISPs have at least five local peers online during the ISP's peak hour, typically in the evening, compared to only 20% of ISPs during the median hour. To better discover these local peers, we show how to increase the overall peer discovery rate by over two orders of magnitude using client-side techniques: leveraging additional trackers, requesting more peers per sample, and sampling more frequently. We propose an approach to predict future availability of local peers based on observed diurnal patterns. This approach enables peers to selectively apply these techniques to minimize undue load on trackers.

Content Delivery Networks (CDNs) rely on the Domain Name System (DNS) for replica server selection. DNS-based server selection builds on the assumption that, in the absence of information about the client's actual network location, the location of a client's DNS resolver provides a good approximation. The recent growth of remote DNS services breaks this assumption and can negatively impact client's web performance.

The Domain Name System (DNS) is a fundamental component of today's Internet. Recent years have seen radical changes to DNS with increases in usage of remote DNS and public DNS services such as OpenDNS. Given the close relationship between DNS and Content Delivery Networks (CDNs) and the pervasive use of CDNs by many popular applications including web browsing and real-time entertainment services, it is important to understand the impact of remote and public DNS services on users' overall experience on the Web. This work presents a tool, namehelp, which comparatively evaluates DNS services in terms of the web performance they provide, and implements an end-host solution to address the performance impact of remote DNS on CDNs. The demonstration will show the functionality of namehelp with online results for its performance improvements.

A thorough understanding of the network impact of emerging large-scale distributed systems -- where traffic flows and what it costs -- must encompass users' behavior, the traffic they generate and the topology over which that traffic flows. In the case of BitTorrent, however, previous studies have been limited by narrow perspectives that restrict such analysis.

Evaluating and characterizing access ISPs is critical to consumers shopping for alternative services and governments surveying the availability of broadband services to their citizens. We present Dasu, a service for crowdsourcing ISP characterization to the edge of the network. Dasu is implemented as an extension to a popular BitTorrent client and has been available since July 2010. While the prototype uses BitTorrent as its host application, its design is agnostic to the particular host application. The demo showcases our current implementation using both a prerecorded execution trace and a live run.

Network positioning systems provide an important service to large- scale P2P systems, potentially enabling clients to achieve higher performance, reduce cross-ISP traffic and improve the robustness of the system to failures. Because traces representative of this environment are generally unavailable, and there is no platform suited for experimentation at the appropriate scale, network positioning systems have been commonly imple- mented and evaluated in simulation and on research testbeds. The performance of network positioning remains an open question for large deployments at the edges of the network. This paper evaluates how four key classes of network po- sitioning systems fare when deployed at scale and measured in P2P systems where they are used. Using 2 billion network measurements gathered from more than 43,000 IP addresses probing over 8 million other IPs worldwide, we show that network positioning exhibits noticeably worse performance than previously reported in studies conducted on research testbeds. To explain this result, we identify several key properties of this environment that call into question fundamental assumptions driving network positioning research.

The user experience for networked applications is becoming a key benchmark for customers and network providers. Perceived user experience is largely determined by the frequency, duration and severity of network events that impact a service. While today's networks implement sophisticated infrastructure that issues alarms for most failures, there remains a class of silent outages (e.g., caused by configuration errors) that are not detected. Further, existing alarms provide little information to help operators understand the impact of network events on services. Attempts to address this through infrastructure that monitors end-to-end performance for customers have been hampered by the cost of deployment and by the volume of data generated by these solutions.

An accurate Internet topology graph is important in many areas of networking, from deciding ISP business relationships to diagnosing network anomalies. Most Internet mapping efforts have derived the network structure, at the level of interconnected autonomous systems (ASes), from a limited number of either BGP- or traceroute- based data sources. While techniques for charting the topology continue to improve, the growth of the number of vantage points is significantly outpaced by the rapid growth of the Internet.

Vehicular networks are emerging as a new distributed system environment with myriad possible applications. Most studies on vehicular networks are carried out via simulation, given the logistical and economical problems with large-scale deployments. This paper investigates the impact of realistic radio propagation settings on the evaluation of VANET-based systems. Using a set of instrumented cars, we collected IEEE 802.11b signal propagation measurements between vehicles in a variety of urban and suburban environments. We found that signal propagation between vehicles varies in different settings, especially between line-of-sight ("down the block") and non line-of-sight ("around the corner") communication in the same setting. Using a probabilistic shadowing model, we evaluate the impact of different parameter settings on the performance of an epidemic data dissemination protocol and discuss the implications of our findings. We also suggest a variation of a basic signal propagation model that incorporates additional realism without sacrificing scalability by taking advantage of environmental information, including node locations and street information.

For both technological and economic reasons, the default path between two end systems in the wide-area Internet can be suboptimal. This observation has motivated a number of systems that attempt to improve reliability and performance by routing over one or more hops in an overlay. Most of the proposed solutions, however, fall at an extreme in the cost-performance trade-off. While some provide near-optimal performance with an un-scalable measurement overhead, others avoid measurement when selecting routes around network failures but make no attempt to optimize performance. This paper presents an experimental evaluation of an alternative approach to scalable, performance detouring based on the strategic reuse of measurements from other large distributed systems, namely content distribution networks (CDNs). By relying on CDN redirections as hints on network conditions, higher performance paths are readily found with little overhead and no active network measurement. We report results from a study of more than 13,700 paths between 170 widely-distributed hosts over a three-week period, showing the benefits of this approach. We demonstrate that it is practical by implementing an FTP suite that uses our publicly available Side Step library to take advantage of these alternative Internet routes.

We consider the problem of data dissemination in vehicular networks. Our main goal is to compare the application-level performance of fully distributed and centralized data dissemination approaches in the context of traffic advisory systems. Vehicular networks are emerging as a new distributed system environment with myriad promising applications. Wirelessly-connected, GPS-equipped vehicles can be used, for instance, as probes for traffic advisory or pavement condition information services with significant improvements in cost, coverage and accuracy. There is an ongoing discussion on the pros and cons of alternative approaches to data distribution for these applications. Proposed centralized, or infrastructure-based, models rely on road-side equipment to upload information to a central location for later use. Distributed approaches take advantage of the direct exchanges between participating vehicles to achieve higher scalability at the potential cost of data consistency. While distributed solutions can significantly reduce infrastructures' deployment and maintenance costs, it is unclear what the impact of "imprecise" information is to an application or what level of adoption is needed for this model to be effective. This paper investigates the inherent trade-offs in the adoption of distributed or centralized approaches to a traffic advisory service, a commonly proposed application. We based our analysis on a measurements study of signal propagation in urban settings and an extensive simulation-based experimentation in the Chicago road network.

Many large-scale distributed systems can benefit from a service that allows them to select among alternative nodes based on their relative network positions. A variety of approaches propose new measurement infrastructures that attempt to scale this service to large numbers of nodes by reducing the amount of direct measurements to end hosts. In this paper, we introduce a new approach to relative network positioning that eliminates direct probing by leveraging pre-existing infrastructure. Specifically, we exploit the dynamic association of nodes with replica servers from large content distribution networks (CDNs) to determine relative position information - we call this approach CDN-based relative network positioning (CRP). We demonstrate how CRP can support two common examples of location information used by distributed applications: server selection and dynamic node clustering. After describing CRP in detail, we present results from an extensive wide-area evaluation that demonstrates its effectiveness.

Peer-to-peer (P2P) systems, which provide a variety of popular services, such as file sharing, video streaming and voice-over-IP, contribute a significant portion of today's Internet traffic. By building overlay networks that are oblivious to the underlying Internet topology and routing, these systems have become one of the greatest traffic-engineering challenges for Internet Service Providers (ISPs) and the source of costly data traffic flows. In an attempt to reduce these operational costs, ISPs have tried to shape, block or otherwise limit P2P traffic, much to the chagrin of their subscribers, who consistently finds ways to eschew these controls or simply switch providers.

We show how to significantly improve the mean response time seen by both uploaders and downloaders in peer-to-peer data-sharing systems. Our work is motivated by the observation that response times are largely determined by the performance of the peers serving the requested objects, that is, by the peers in their capacity as servers. With this in mind, we take a close look at this server side of peers, characterizing its workload by collecting and examining an extensive set of traces. Using trace-driven simulation, we demonstrate the promise and potential problems with scheduling policies based on shortest-remaining-processing-time (SRPT), the algorithm known to be optimal for minimizing mean response time. The key challenge to using SRPT in this context is determining request service times. In addressing this challenge, we introduce two new estimators that enable predictive SRPT scheduling policies that closely approach the performance of ideal SRPT. We evaluate our approach through extensive single-server and system-level simulation coupled with real Internet deployment and experimentation.

Packet forwarding prioritization (PFP) in routers is one of the mechanisms commonly available to network administrators. PFP can have a significant impact on the performance of applications, the accuracy of measurement tools' results and the effectiveness of network troubleshooting procedures. Despite their potential impact, no information on PFP settings is readily available to end users. In this paper, we present an end-to-end approach for packet forwarding priority inference and its associated tool, POPI. This is the first attempt to infer router packet-forwarding priority through end-to-end measurement. Our POPI tool enables users to discover such network policies through the monitoring and rank classification of loss rates for different packet types. We validated our approach via statistical analysis, simulation, and wide-area experimentation in PlanetLab. As part of our wide-area experiments, we employed POPI to analyze 156 random paths across 162 PlanetLab nodes. We discovered 15 paths flagged with multiple priorities, 13 of which were further validated through hop-by-hop loss rates measurements. In addition, we surveyed all related network operators and received responses for about half of them confirming our inferences.

Overlay-based multicast has been proposed as a key alternative for large-scale group communication. There is ample motivation for such an approach, as it delivers the scalability advantages of multicast while avoiding the deployment issues of a network-level solution. As multicast functionality is pushed to autonomous, unpredictable end systems, however, significant performance loss can result from their higher degree of transiency when compared to routers. Consequently, a number of techniques have recently been proposed to improve overlays' resilience by exploiting path diversity and minimizing node dependencies. Delivering high application performance at relatively low costs and under high degree of transiency has proven to be a difficult task. Each of the proposed resilient techniques comes with a different trade-off in terms of delivery ratio, end-to-end latency and additional network traffic. In this paper, we review some of these approaches and evaluate their effectiveness by contrasting the performance and associated cost of representative protocols through simulation and wide area experimentation.

One of the most important challenges of selforganized, overlay systems for large-scale group communication lies in these systems ability to handle the high degree of transiency inherent to their environment. While a number of resilient protocols and techniques have been recently proposed, achieving high delivery ratios without sacrificing end-to-end latencies or incurring significant additional costs has proven to be a difficult task. In this paper we review some of these approaches and experimentally evaluate their effectiveness by contrasting their performance and associated cost through simulation and widearea experimentation.

To enhance web browsing experiences, content distribution networks (CDNs) move web content "closer" to clients by caching copies of web objects on thousands of servers worldwide. Additionally, to minimize client download times, such systems perform extensive network and server measurements, and use them to redirect clients to different servers over short time scales. In this paper, we explore techniques for inferring and exploiting network measurements performed by the largest CDN, Akamai; our objective is to locate and utilize quality Internet paths without performing extensive path probing or monitoring.Our contributions are threefold. First, we conduct a broad measurement study of Akamai's CDN. We probe Akamai's network from 140 PlanetLab vantage points for two months. We find that Akamai redirection times, while slightly higher than advertised, are sufficiently low to be useful for network control. Second, we empirically show that Akamai redirections overwhelmingly correlate with network latencies on the paths between clients and the Akamai servers. Finally, we illustrate how large-scale overlay networks can exploit Akamai redirections to identify the best detouring nodes for one-hop source routing. Our research shows that in more than 50% of investigated scenarios, it is better to route through the nodes "recommended" by Akamai, than to use the direct paths. Because this is not the case for the rest of the scenarios, we develop lowoverhead pruning algorithms that avoid Akamai-driven paths when they are not beneficial.

DualPats exploits the strong correlation between TCP throughput and flow size, and the statistical stability of Internet path characteristics to accurately predict the TCP throughput of large transfers using active probing. We propose additional mechanisms to explain the correlation, and then analyze why traditional TCP benchmarking fails to predict the throughput of large transfers well. We characterize stability and develop a dynamic sampling rate adjustment algorithm so that we probe a path based on its stability. Our analysis, design, and evaluation is based on a large-scale measurement study.

We explore the feasibility of streaming applications over DHT-based substrates. In particular, we focus our study on the implications of bandwidth heterogeneity and transiency, both characteristic of these systems target environment. Our discussion is grounded on an initial evaluation of SplitStream, a representative DHT-based cooperative multicast system.

We address the problem of highly transient populations in unstructured and loosely-structured peer-to-peer systems. We propose a number of illustrative query-related strategies and organizational protocols that, by taking into consideration the expected session times of peers (their lifespans), yield systems with performance characteristics more resilient to the natural instability of their environments. We first demonstrate the benefits of lifespan-based organizational protocols in terms of end-application performance and in the context of dynamic and heterogeneous Internet environments. We do this using a number of currently adopted and proposed query-related strategies, including methods for query distribution, caching and replication. We then show, through trace-driven simulation and wide-area experimentation, the performance advantages of lifespan-based, query-related strategies when layered over currently employed and lifespan-based organizational protocols. While merely illustrative, the evaluated strategies and protocols clearly demonstrate the advantages of considering peers' session time in designing widely-deployed peer-to-peer systems.

This work introduces Nemo, a novel peer-to-peer multicast protocol that aims at achieving this elusive goal. Based on two techniques: (1) co-leaders; and, (2) triggered negative acknowledgments (NACKs), Nemo's design emphasizes conceptual simplicity and minimum dependencies (Anderson et al., 2002), thus achieving, in a cost-effective manner, performance characteristics resilient to the natural instability of its target environment. Simulation-based and wide-area experimentations show that Nemo can achieve high delivery ratios (up to 99.98%) and low end-to-end latency similar to those of comparable protocols, while significantly reducing the cost in terms of duplicate packets (reductions > 85%) and control related traffic, making the proposed algorithm a more scalable solution to the problem.

We present a mechanism for providing differential data protection to publish/subscribe distributed systems, such as those used in peer-to-peer computing, grid environments, and others. This mechanism, termed "security overlays", incorporates credential-based communication channel creation, subscription and extension. We describe a conceptual model of publish/subscribe services that is made concrete by our mechanism. We also present an application, active video streams, whose reimplementation using security overlays allows it to react to high-level security policies specified in XML without significant performance loss or the necessity for embedding policy-specific code into the application.

In this paper, we argue that an exclusively inactive interface to directory services can hinder server scalability and indirectly restrict the behavior of potential applications. We propose to extend directory services' interfaces with a proactive mode by which clients can express their interest in (and be notified of) changes in the environment. These notification channels can be subsequently customized on a per-client basis through client-specified filters. Finally, in order to simplify the handling of client/server failures we adopt a leasing model for client registration to (and customization of) a notification channel. To validate our approach, we have designed and implemented the Proactive Directory Service (PDS).

Common to computational grids and pervasive computing is the need for an expressive, efficient, and scalable directory service that provides information about objects in the environment. We argue that a directory interface that ‘pushes’ information to clients about changes to objects can significantly improve scalability. This paper describes the design, implementation, and evaluation of the Proactive Directory Service (PDS). PDS’ interface supports a customizable ‘proactive’ mode through which clients can subscribe to be notified about changes to their objects of interest. Clients can dynamically tune the detail and granularity of these notifications through filter functions instantiated at the server or at the object’s owner, and by remotely tuning the functionality of those filters. We compare PDS’ performance against off-the-shelf implementations of DNS and the Lightweight Directory Access Protocol. Our evaluation results confirm the expected performance advantages of this approach and demonstrate that customized notification through filter functions can reduce bandwidth utilization while improving the performance of both clients and directory servers.

New trends in high-performance software development such as tool- and component-based approaches have increased the need for flexible and high-performance communication systems. When trying to reap the well-known benefits of these approaches, the question of what communication infrastructure should be used to link the various components arises. In this context, flexibility and high-performance seem to be incompatible goals. Traditional HPC-style communication libraries, such as MPI, offer good performance, but are not intended for loosely-coupled systems. Object- and metadata-based approaches like XML offer the needed plug-and-play flexibility, but with significantly lower performance. We observe that the flexibility and baseline performance of data exchange systems are strongly determined by their wire formats, or by how they represent data for transmission in heterogeneous environments. After examining the performance implications of using a number of different wire formats, we propose an alternative approach for flexible high-performance data exchange, Native Data Representation, and evaluate its current implementation in the portable binary I/O library.

Summary form only given. An increasing number of distributed applications aim to provide services to users by interacting with a correspondingly growing set of data-intensive network services. To support such requirements, we believe that new services need to be customizable, applications need to be dynamically extensible, and both applications and services need to be able to adapt to variations in resource availability and demand. A comprehensive approach to building new distributed applications can facilitate this by considering the contents of the information flowing across the application and its services and by adopting a component-based model to application/service programming. It should provide for dynamic adaptation at multiple levels and points in the underlying platform; and, since the mapping of components to resources in dynamic environment is too complicated, it should relieve programmers of this task. We propose Active Streams, a middleware approach and its associated framework for building distributed applications and services that exhibit these characteristics.

The explosive growth of the Internet, with the emergence of new networking technologies and the increasing number of network-capable end devices, is paving the way for a number of novel distributed applications and services. Cooperative distributed systems have become a common computing model, and pervasive computing has caught the interest of academia and industry. To support future network applications, we believe that new services need to be customizable, applications need to be dynamically extensible, and both applications and services should be able to adapt to variations in resource availability and demand. propose Active Streams (F.E. Bustamante and K. Schwan, 1999), a middleware approach and its associated framework for building distributed applications and services that exhibit these characteristics.

The Internet and the Grid are changing the face of high-performance computing. Rather than tightly-coupled SPMD-style components running in a single cluster, on a parallel machine, or even on the Internet programmed in MPI, applications are evolving into sets of collaborating components scattered across diverse computational elements. These collaborating components may run on different operating systems and hardware platforms and may be written by different organizations in different languages. Complete "applications" are constructed by assembling these components in a plug-and-play fashion. This new vision for high-performance computing demands features and characteristics which are not easily provided by traditional high-performance communications middleware. In response to these needs, we have developed ECho, a high-performance event-delivery middleware that meets the new demands of the Grid environment. ECho provides efficient binary transmission of event data with unique features that support data-type discovery and enterprise-scale application evolution. We present measurements detailing ECho's performance to show that ECho significantly outperforms other systems intended to provide this functionality, and that it provides throughput and latency comparable to the most efficient middleware infrastructures available.

High performance computing is being increasingly utilized in non-traditional circumstances where it must interoperate with other applications. For example, online visualization is being used to monitor the progress of applications, and real-world sensors are used as inputs to simulations. Whenever these situations arise, there is a question of what communications infrastructure should be used to link the different components. Traditional HPC-style communications systems such as MPI offer relatively high performance, but are poorly suited for developing these less tightly-coupled cooperating applications. Object-based systems and meta-data formats like XML offer substantial plug-and-play flexibility, but with substantially lower performance. We observe that the flexibility and baseline performance of all these systems is strongly determined by their `wire format', or how they represent data for transmission in a heterogeneous environment. We examine the performance implications of different wire formats and present an alternative with significant advantages in terms of both performance and flexibility.