Constantine Dovrolis

An experimental evaluation of rate-adaptation algorithms in adaptive streaming over HTTP

Adaptive (video) streaming over HTTP is gradually being adopted, as it offers significant advantages in terms of both user-perceived quality and resource utilization for content and network service providers. In this paper, we focus on the rate-adaptation mechanisms of adaptive streaming and experimentally evaluate two major commercial players (Smooth Streaming, Netflix) and one open source player (OSMF). Our experiments cover three important operating conditions. First, how does an adaptive video player react to either persistent or short-term changes in the underlying network available bandwidth. Can the player quickly converge to the maximum sustainable bitrate? Second, what happens when two adaptive video players compete for available bandwidth in the bottleneck link? Can they share the resources in a stable and fair manner? And third, how does adaptive streaming perform with live content? Is the player able to sustain a short playback delay? We identify major differences between the three players, and significant inefficiencies in each of them.

What happens when HTTP adaptive streaming players compete for bandwidth

With an increasing demand for high-quality video content over the Internet, it is becoming more likely that two or more adaptive streaming players share the same network bottleneck and compete for available bandwidth. This competition can lead to three performance problems: player instability, unfairness between players, and bandwidth underutilization. However, the dynamics of such competition and the root cause for the previous three problems are not yet well understood. In this paper, we focus on the problem of competing video players and describe how the typical behavior of an adaptive streaming player in its Steady-State, which includes periods of activity followed by periods of inactivity (ON-OFF periods), is the main root cause behind the problems listed above. We use two adaptive players to experimentally showcase these issues. Then, focusing on the issue of player instability, we test how several factors (the ON-OFF durations, the available bandwidth and its relation to available bitrates, and the number of competing players) affect stability.

Open issues in router buffer sizing

Recent research results suggest that the buffers of router interfaces can be made very small, much less than the links and width-delay product, without causing a utilization loss, as long as the link carries many TCP flows. In this letter we raise some concerns about the previous recommendation. We show that the use of such small buffers can lead to excessively high loss rates (up to 5%-15%in our simulations) in congested access links that carry many flows. Even if the link is fully utilized, small buffers lead to lower throughput for most large TCP flows, and significant variability in the per-flow throughput and transfer latency. We also discuss some important issues in router buffer sizing that are often ignored

The Internet is flat: modeling the transition from a transit hierarchy to a peering mesh

Recent measurements and anecdotal evidence indicate that the Internet ecosystem is rapidly evolving from a multi-tier hierarchy built mostly with transit (customer-provider) links to a dense mesh formed with mostly peering links. This transition can have major impact on the global Internet economy as well as on the traffic flow and topological structure of the Internet. In this paper, we study this evolutionary transition with an agent-based network formation model that captures key aspects of the interdomain ecosystem, viz., interdomain traffic flow and routing, provider and peer selection strategies, geographical constraints, and the economics of transit and peering interconnections. The model predicts several substantial differences between the Hierarchical Internet and the Flat Internet in terms of topological structure, path lengths, interdomain traffic flow, and the profitability of transit providers. We also quantify the effect of the three factors driving this evolutionary transition. Finally, we examine a hypothetical scenario in which a large content provider produces more than half of the total Internet traffic.

Server-based traffic shaping for stabilizing oscillating adaptive streaming players

Prior work has shown that two or more adaptive streaming players can be unstable when they compete for bandwidth. The root cause of the instability problem is that, in Steady-State, a player goes through an ON-OFF activity pattern in which it overestimates the available bandwidth. We propose a server-based traffic shaping method that can significantly reduce such oscillations without significant (or any) loss in bandwidth utilization. The shaper is only activated when oscillations are detected, and it dynamically adjusts the shaping rate so that the player should ideally receive the highest available video profile while being stable. We evaluate the proposed method experimentally in terms of instability and utilization comparing with the unshaped case, under several scenarios.

NetDiagnoser: troubleshooting network unreachabilities using end-to-end probes and routing data

The distributed nature of the Internet makes it difficult for a single service provider to troubleshoot the disruptions experienced by its customers. We propose NetDiagnoser, a troubleshooting algorithm to identify the location of failures in an internetwork environment. First, we adapt the well-known Boolean tomography technique to work in this environment. Then, we significantly extend this technique to improve the diagnosis accuracy in the presence of multiple link failures, logical failures (for instance, misconfigurations of route export filters), and incomplete topology inference. In particular, NetDiagnoser takes advantage of rerouted paths, routing messages collected at one providers network and Looking Glass servers. We evaluate each feature of Net-Diagnoser separately using C-BGP simulations on realistic topologies. Our results show that NetDiagnoser can successfully identify a small set of links, which almost always includes the actually failed/misconfigured links.

Future Internet architecture: clean-slate versus evolutionary research

Should researchers focus on designing new network architectures or improving the current Internet?

Twelve years in the evolution of the internet ecosystem

Our goal is to understand the evolution of the autonomous system (AS) ecosystem over the last 12 years. Instead of focusing on abstract topological properties, we classify ASs into a number of types depending on their function and business type. Furthermore, we consider the semantics of inter-AS links: customer-provider versus peering relations. We find that the available historic datasets from RouteViews and RIPE are not sufficient to infer the evolution of peering links, and so we restrict our focus to customer-provider links. Our findings highlight some important trends in the evolution of the Internet over the last 12 years and hint at what the Internet is heading toward. After an exponential increase phase until 2001, the Internet has settled into a slower exponential growth in terms of both ASs and inter-AS links. The growth is mostly due to enterprise networks and content/access providers at the periphery of the Internet. The average path length remains almost constant, mostly due to the increasing multihoming degree of transit and content/access providers. The AS types differ significantly from each other with respect to their rewiring activity; content/access providers are the most active. A few large transit providers act as “attractors” or “repellers” of customers. For many providers, strong attractiveness precedes strong repulsiveness by 3-9 months. Finally, in terms of regional growth, we find that the AS ecosystem is now larger and more dynamic in Europe than in North America.

One-click hosting services: a file-sharing hideout

File sharing using peer-to-peer (p2p) systems is a major Internet application and the leading source of network traffic today. However, the dominance of p2p systems for file sharing has been recently challenged by an increasing number of services, such as RapidShare and MegaUpload, which offer users the ability to share files through centralized servers, without relying on an underlying p2p infrastructure. These services, referred to as One-Click Hosting (OCH), have the potential to offer users better performance and availability than p2p systems. If they succeed, OCH services may become the leading platform for file sharing and eventually replace p2p systems for this purpose. In this paper, we present the first, to our knowledge, detailed study of OCH traffic and services focusing on the most popular such service: RapidShare. Through a combination of passive and active measurements, we attempt to understand their service architecture, usage patterns, and content characteristics. We also compare RapidShare with BitTorrent in terms of user-perceived throughput and content availability, and we explore the characteristics of some popular RapidShare indexing sites.

The probe gap model can underestimate the available bandwidth of multihop paths

The Probe Gap Model (PGM) was proposed as a lightweight and fast available bandwidth estimation method. Measurement tools such as Delphi and Spruce are based on PGM. Compared to estimation methods that require multiple iterations with different probing rates, PGM uses a single probing rate and it infers the available bandwidth from a direct relation between the input and output rates of measurement packet pairs. An important assumption behind the PGM model is that the measured path has a single bottleneck link that determines the available bandwidth of the end-to-end path. In this letter, we show that, even though PGM is accurate in the case of a single queue, it cannot estimate the available bandwidth of multi-hop paths, even if there is a single bottleneck in the path. Whether PGM is accurate or not depends on the routing of cross traffic relative to the measurement traffic. PGM is accurate when the cross traffic follows the same path with the measurement traffic. In the general case, however, PGM can significantly underestimate the available bandwidth of an end-to-end path.