Recent work has focused on increasing availability in the face of Internet path failures. To date, proposed solutions have relied on complex routing and pathmonitoring schemes, trading scalability for availability among a relatively small set of hosts. This paper proposes a simple, scalable approach to recover from Internet path failures. Our contributions are threefold. First, we conduct a broad measurement study of Internet path failures on a collection of 3,153 Internet destinations consisting of popular Web servers, broadband hosts, and randomly selected nodes. We monitored these destinations from 67 PlanetLab vantage points over a period of seven days, and found availabilities ranging from 99.6 % for servers to 94.4 % for broadband hosts. When failures do occur, many appear too close to the destination (e.g., last-hop and end-host failures) to be mitigated through alternative routing techniques of any kind. Second, we show that for the failures that can be addressed through routing, a simple, scalable technique, called one-hop source routing, can achieve close to the maximum benefit available with very low overhead. When a path failure occurs, our scheme attempts to recover from it by routing indirectly through a small set of randomly chosen intermediaries. Third, we implemented and deployed a prototype onehop source routing infrastructure on PlanetLab. Over a three day period, we repeatedly fetched documents from 982 popular Internet Web servers and used one-hop source routing to attempt to route around the failures we observed. Our results show that our prototype successfully recovered from 56 % of network failures. However, we also found a large number of server failures that cannot be addressed through alternative routing. Our research demonstrates that one-hop source routing is easy to implement, adds negligible overhead, and achieves close to the maximum benefit available to indirect routing schemes, without the need for path monitoring, history, or a-priori knowledge of any kind. 1

The views and conclusions contained in this document are those of the authors and should not be interpreted as The ability to locate network bottlenecks along end-to-end paths on the Internet is of great interest to both network operators and researchers. For example, knowing where bottleneck links are, network operators can apply traffic engineering either at the interdomain or intradomain level to improve routing. Existing bandwidth measurement tools fail to identify the location of bottleneck links. In addition, they often require access to both end points and generate huge amount of probing packets. These drawbacks make them impractical. In this paper, we present a novel light-weight, single-end active probing tool – Pathneck – based a novel probing technique called Recursive Packet Train (RPT), which allows end users to efficiently and accurately locate bottleneck points to destinations on the Internet. We evaluate Pathneck using trace-driven emulations and wide area Internet experiments. In addition, we conduct extensive measurements on the Internet among carefully selected, geographically diverse probing sources and destinations to study Internet bottleneck properties. We find that Pathneck can successfully detect bottlenecks for over 70% of paths, and most of the bottlenecks are fairly stable. We also report our success on bottleneck

Abstract — Recently, overlay networks have emerged as a means to enhance end-to-end application performance and availability. Overlay networks attempt to leverage the inherent redundancy of the Internet’s underlying routing infrastructure to detour packets along an alternate path when the given primary path becomes unavailable or suffers from congestion. However, the effectiveness of these overlay networks depends on the natural diversity of overlay paths between two endhosts in terms of physical links, routing infrastructure, administrative control, and geographical distribution. Several recent studies realized that a measurable number of path outages were unavoidable even with use of such overlay networks. This stems from the fact that overlay paths might overlap with each other when overlay nodes are selected without considering the underlying topology. An overlay network’s ability to quickly recover from path outages and congestion is limited unless we ensure path independence at the IP layer. This paper proposes a novel framework for topologyaware overlay networks. In this framework, we expressly design overlay networks, aiming to maximize path independence without degrading performance. We develop measurement-based heuristics for 1) placement of overlay nodes inside an ISP and 2) selection of a set of ISPs. We base our analysis on extensive data collection from 232 points in 10 ISPs, and 100 PlanetLab nodes. On top of node placement, we present measurement-based verification to conclude that single-hop overlay routing performs as well as multi-hop routing with respect to both availability and performance. Our analysis results show that a single-hop overlay path provides the same degree of path diversity as the multihop overlay path for more than 90 % of source and destination pairs. Finally, we validate the proposed framework using real Internet outages to show that our architecture is able to provide a significant amount of resilience to real-world failures. I.

We present path splicing, a new routing primitive that allows network paths to be constructed by combining multiple routing trees (“slices”) to each destination over a single network topology. Path splicing allows traffic to switch trees at any hop en route to the destination. End systems can change the path on which traffic is forwarded by changing a small number of additional bits in the packet header. We evaluate path splicing for intradomain routing using slices generated from perturbed link weights and find that splicing achieves reliability that approaches the best possible using a small number of slices, for only a small increase in latency and no adverse effects on traffic in the network. In the case of interdomain routing, where splicing derives multiple trees from edges in alternate backup routes, path splicing achieves near-optimal reliability and can provide significant benefits even when only a fraction of ASes deploy it. We also describe several other applications of path splicing, as well as various possible deployment paths.

Dynamic overlay routing has been proposed as a way to enhance the reliability and performance of IP networks. The major premise is that overlay routing can bypass congestion, transient outages, or suboptimal paths, by forwarding traffic through one or more intermediate overlay nodes. In this paper, we perform an extensive simulation study to investigate the performance of dynamic overlay routing. In particular, we leverage recent work on available bandwidth (avail-bw) estimation, and focus on overlay routing that selects paths based on avail-bw measurements between adjacent overlay nodes. First, we compare two overlay routing algorithms, reactive and proactive, with shortest-path native routing. We show that reactive routing has significant benefits in terms of throughput and path stability, while proactive routing is better in providing flows with a larger safety margin (“headroom”), and propose a hybrid routing scheme that combines the best features of the previous two algorithms. We then examine the effect of several factors, including network load, traffic variability, link-state staleness, number of overlay hops, measurement errors, and native sharing effects. Some of our results are rather ∗ This work was supported by the NSF CAREER award ANIR-0347374, and by a Georgia Tech Broadband Institute (GTBI) grant. surprising. For instance, we show that a significant measurement error, even up to 100 % of the actual avail-bw value, has a negligible impact on the efficiency of overlay routing. 1

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Dynamic load balancing is a popular recent technique that protects ISP networks from sudden congestion caused by load spikes or link failures. Dynamic load balancing protocols, however, require schemes for splitting traffic across multiple paths at a fine granularity. Current splitting schemes present a tussle between slicing granularity and packet reordering. Splitting traffic at the granularity of packets quickly and accurately assigns the desired traffic share to each path, but can reorder packets within a TCP flow, confusing TCP congestion control. Splitting traffic at the granularity of a flow avoids packet reordering but may overshoot the desired shares by up to 60 % in dynamic environments, resulting in low end-to-end network goodput. Contrary to popular belief, we show that one can systematically split a single flow across multiple paths without causing packet reordering. We propose FLARE, a new traffic splitting algorithm that operates on bursts of packets, carefully chosen to avoid reordering. Using a combination of analysis and trace-driven simulations, we show that FLARE attains accuracy and responsiveness comparable to packet switching without reordering packets. FLARE is simple and can be implemented with a few KB of router state.

Abstract — The cost savings and novel features associated with Voice over IP (VoIP) are driving its adoption by service providers. Unfortunately, the Internet’s best effort service model provides no quality of service guarantees. Because low latency and jitter is the key requirement for supporting high quality interactive conversations, VoIP applications use UDP to transfer data, thereby subjecting themselves to quality degradations caused by packet loss and network failures. In this paper we describe an architecture to improve the performance of such VoIP applications. Two protocols are used for localized packet loss recovery and rapid rerouting in the event of network failures. The protocols are deployed on the nodes of an application-level overlay network and require no changes to the underlying infrastructure. Experimental results indicate that the architecture and protocols can be combined to yield voice quality on par with the PSTN. I.

The MIT RON testbed consists of 36 Internet-connected nodes at 31 different sites. It has been in operation for two years. This paper presents an overview of the testbed, summarizes some of the research for which it has proved useful, and presents the lessons we learned during its development. The testbed has been useful both for our own research and for that of external researchers because of its heterogeneous, diverse network connections; its homogenous hardware and software platform; its incremental, bottom-up development; and its easy configuration and management tools.

Voice traffic on the Internet (VoIP) is poised to grow rapidly but the Internet is not engineered for such delay-sensitive applications. We show how the end-user quality of many VoIP calls can be improved by rerouting them in an intermediate overlay network and thought the use of various path-diversity and error-coding techniques. We present an overlay network (OverPhone) that is tuned to optimize VoIP quality and provide experimental results based on its implementation on the PlanetLab testbed. We show that about a third of the VoIP calls show noticable performance improvement when re-routed through the overlay while using the G.711 codec. We believe that this benefit extends to other well known and proprietary codecs as well. We also investigate the benefits and trade-offs of using techniques such as path-diversity and parity-coding. We find that path-diversity is useful in sustaining throughput at high loads,