Zachary S. Bischof

SIDnet-SWANS: a simulator and integrated development platform for sensor networks applications

This work presents the SIDnet, a simulation-based environment for applications development in wireless sensor networks settings. It enables run-time interactions with the network for the purpose of observing the behavior of algorithms protocols in the presence of various conditions such as phenomena fluctuations, or a sudden loss of service both at an individual node, as well as a collection of nodes.

Crowdsourcing ISP characterization to the network edge

Evaluating and characterizing Internet Service Providers (ISPs) is critical to subscribers shopping for alternative ISPs, companies providing reliable Internet services, and governments surveying the coverage of broadband services to its citizens. Ideally, ISP characterization should be done at scale, continuously, and from end users. While there has been significant progress toward this end, current approaches exhibit apparently unavoidable tradeoffs between coverage, continuous monitoring and capturing user-perceived performance. In this paper, we argue that network-intensive applications running on end systems avoid these tradeoffs, thereby offering an ideal platform for ISP characterization. Based on data collected from 500,000 peer-to-peer BitTorrent users across 3,150 networks, together with the reported results from the U.K. Ofcom/SamKnows studies, we show the feasibility of this approach to characterize the service that subscribers can expect from a particular ISP. We discuss remaining research challenges and design requirements for a solution that enables efficient and accurate ISP characterization at an Internet scale.

Up, down and around the stack: ISP characterization from network intensive applications

Broadband characterization has recently attracted much attention from the research community and the general public. Given this interest and the important business and policy implications of residential Internet service characterization, recent years have brought a variety of approaches to profiling Internet services, ranging from Web-based platforms to dedicated infrastructure inside home networks. We have previously argued that network-intensive applications provide an almost ideal vantage point for broadband service characterization at sufficient scale, nearly continuously and from end users. While we have shown that the approach is indeed effective at characterization and can enable performance comparisons between service providers and geographic regions, a key unanswered question is how well the performance characteristics captured by these network-intensive applications can predict the overall user experience with other applications. In this paper, using BitTorrent as an example network-intensive application, we present initial results that demonstrate how to obtain estimates of bandwidth and latency of a network connection by leveraging passive monitoring and limited active measurements from network intensive applications. We then analyze user experienced web performance under a variety of network conditions and show how estimated metrics from this network intensive application can serve as good web performance predictors.

In and Out of Cuba: Characterizing Cuba's Connectivity

The goal of our work is to characterize the current state of Cubas 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 Cubas 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.

Controlled Multi-Path Routing in Sensor Networks Using Bezier Curves

We address the problem of extending the lifetime of wireless sensor networks using multi-path routing based on a family of flexible routes with soft quality of service guarantees in terms of the packets’ delivery latency. We introduce a methodology based on Bezier curves as guiding trajectories in the routing process and we address the balancing of the workload among neighboring nodes. An added benefit, due to the flexibility of the Bezier curves, is that the shapes of the (alternate) routes can be constructed in a manner that prolongs the lifetime of the nodes in the vicinity of a given source/sink. We describe a forwarding algorithm, where the relay nodes can determine locally the Bezier curve they belong to and which requires only the transmission of the so-called control points that determine the shape of one (boundary) curve. We also show how our forwarding algorithm can be adapted to incorporate the sleep-schedule of the individual nodes, thereby further prolonging the networks’ lifetime. Our simulations demonstrate that the Bezier-based routing algorithms can yield significant improvements in the networks’ overall lifetime.

Need, Want, Can Afford: Broadband Markets and the Behavior of Users

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.

Trying broadband characterization at home

In recent years the quantity and diversity of Internet-enabled consumer devices in the home have increased significantly. These trends complicate device usability and home resource management and have implications for crowdsourced approaches to broadband characterization. The UPnP protocol has emerged as an open standard for device and service discovery to simplify device usability and resource management in home networks. In this work, we leverage UPnP to understand the dynamics of home device usage, both at a macro and micro level, and to sketch an effective approach to broadband characterization that runs behind the last meter. Using UPnP measurements collected from over 13K end users, we show that while home networks can be quite complex, the number of devices that actively and regularly connect to the Internet is limited. Furthermore, we find a high correlation between the number of UPnP-enabled devices in home networks and the presence of UPnP-enabled gateways, and show how this can be leveraged for effective broadband characterization.

Distributed systems and natural disasters: BitTorrent as a global witness

Peer-to-peer (P2P) systems represent some of the largest distributed systems in todays Internet. Among P2P systems, BitTorrent is the most popular, potentially accounting for 20--50% of P2P file-sharing traffic. In this paper, we argue that this popularity can be leveraged to monitor the impact of natural disasters and political unrest on the Internet. We focus our analysis on the 2011 Tohoku earthquake and tsunami and use a view from BitTorrent to show that it is possible to identify specific regions and network links where Internet usage and connectivity were most affected.

A measurement experimentation platform at the internet's edge

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. Todays 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 Internets edge, describe its design and implementation, and illustrate the unique perspective its current deployment brings to Internet measurement.

Dasu - ISP characterization from the edge: a BitTorrent implementation

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.