Tobias Flach

• Master of Science
• Research Assistant at University of Southern California

To serve users quickly, Web service providers build infrastructure closer to clients and use multi-stage transport connections. Although these changes reduce client-perceived round-trip times, TCP's current mechanisms fundamentally limit latency improvements. We performed a measurement study of a large Web service provider and found that, while con...

As mobile Internet becomes more popular, carriers and content providers must engineer their topologies, routing configurations, and server deployments to maintain good performance for users of mobile devices. Understanding the impact of Internet topology and routing on mobile users requires broad, longitudinal network measurements conducted from mo...

Initially, packet forwarding in the Internet was destination-based -- that is, a router would forward all packets with the same destination address to the same next hop. In this paper, we use active probing methods to quantify and characterize deviations from destination-based forwarding in today's Internet. From over a quarter million probes, we a...

Large flows like videos consume significant bandwidth. Some ISPs actively manage these high volume flows with techniques like policing, which enforces a flow rate by dropping excess traffic. While the existence of policing is well known, our contribution is an Internet-wide study quantifying its prevalence and impact on video quality metrics. We de...

People increasingly use mobile devices as their primary means to access the Internet. While it is well known that cellular network operators employ middleboxes, the details of their behavior and their impact on Web performance are poorly understood. This paper presents an analysis of proxy behavior and how transparent Web proxies interact with HTTP...

Transient performance anomalies when accessing websites can be hard to replicate and make it difficult to detect and remedy their root causes. We propose a tool which passively monitors browser behavior and network traffic, while actively probing the network when detecting performance anomalies, and determining their root causes.

To serve users quickly, Web service providers build infrastructure closer to clients and use multi-stage transport connections. Although these changes reduce client-perceived round-trip times, TCP's current mechanisms fundamentally limit latency improvements. We performed a measurement study of a large Web service provider and found that, while con...

Ordinary TCP loss recovery takes at least one round-trip time and as such can increase application-perceived latency, especially for short flows such as Web transactions. TCP Instant Recovery (TCP-IR) is an experimental algorithm that allows a receiving end to recover lost packets without retransmissions, thus potentially saving at least one full r...

Wireless sensing and actuation have been explored in many contexts, but the automotive setting has received relatively little attention. Automobiles have tens of onboard sensors and expose several hundred engine parameters which can be tuned (a form of actuation). The optimal tuning for a vehicle can depend upon terrain, traffic, and road condition...

Increasing energy costs became one of the critical issues in database centers in the recent years. The consciousness to turn towards energy-preserving technologies have put concepts like power-awareness into the spotlight. But especially databases lack the capability of managing the energy consumption while operating and past research solely focuss...

With the development of the Near Field Communication (NFC) technology for fast and comfortable data exchange between mobile and other devices new fields of application become available for mobile phones. In this paper we evaluate realistic application domains and present an implementation for a selected scenario: the exchange of contact data betwee...