A Resilient Overlay Network (RON) is an architecture that allows distributed Internet applications to detect and recover from path outages and periods of degraded performance within several seconds, improving over today’s wide-area routing protocols that take at least several minutes to recover. A RON is an application-layer overlay on top of the existing Internet routing substrate. The RON nodes monitor the functioning and quality of the Internet paths among themselves, and use this information to decide whether to route packets directly over the Internet or by way of other RON nodes, optimizing application-specific routing metrics. Results from two sets of measurements of a working RON deployed at sites scattered across the Internet demonstrate the benefits of our architecture. For instance, over a 64-hour sampling period in March 2001 across a twelve-node RON, there were 32 significant outages, each lasting over thirty minutes, over the 132 measured paths. RON’s routing mechanism was able to detect, recover, and route around all of them, in less than twenty seconds on average, showing that its methods for fault detection and recovery work well at discovering alternate paths in the Internet. Furthermore, RON was able to improve the loss rate, latency, or throughput perceived by data transfers; for example, about 5 % of the transfers doubled their TCP throughput and 5 % of our transfers saw their loss probability reduced by 0.05. We found that forwarding packets via at most one intermediate RON node is sufficient to overcome faults and improve performance in most cases. These improvements, particularly in the area of fault detection and recovery, demonstrate the benefits of moving some of the control over routing into the hands of end-systems.

The demand for streaming multimedia applications is growing at an incredible rate. In this paper, we propose Bayeux, an efficient application-level multicast system that scales to arbitrarily large receiver groups while tolerating failures in routers and network links. Bayeux also includes specific mechanisms for load-balancing across replicate root nodes and more efficient bandwidth consumption. Our simulation results indicate that Bayeux maintains these properties while keeping transmission overhead low. To achieve these properties, Bayeux leverages the architecture of Tapestry, a fault-tolerant, wide-area overlay routing and location network.

The IP multicast model allows scalable and efficient multi-party communication, particularly for groups of large size. However, deployment of IP multicast requires substantial infrastructure modifications and is hampered by a host of unresolved open problems. To circumvent this situation, we have designed and implemented ALMI, an application level group communication middleware, which allows accelerated application deployment and simplified network configuration, without the need of network infrastructure support. ALMI is tailored toward support of multicast groups of relatively small size (several I Os of members) with many to many semantics. Session participants are connected via a vir- tual multicast tree, which consists of unicast connections between end hosts and is formed as a minimum spanning tree (MST) using application-specific performance metric. Using simulation, we show that the performance penalties, introduced by this shift of multicast to end systems, is a relatively small increase in traffic load and that ALMI multicast trees approach the efficiency of IP multicast trees. We have also implemented ALMi as a Java based middleware package and performed experiments over the Internet. Experimental results show that ALMI is able to cope with network dynamics and keep the mul- ticast tree efficient.

The widespread deployment of inexpensive communications technology, computational resources in the networking infrastructure, and network-enabled end devices poses an interesting problem for end users: how to locate a particular network service or device out of hundreds of thousands of accessible services and devices. This paper presents the architecture and implementation of a secure Service Discovery Service (SDS). Service providers use the SDS to advertise complex descriptions of available or already running services, while clients use the SDS to compose complex queries for locating these services. Service descriptions and queries use the eXtensible Markup Language (XML) to encode such factors as cost, performance, location, and device- or service-specific capabilities. The SDS provides a highlyavailable, fault-tolerant, incrementally scalable service for locating services in the wide-area. Security is a core component of the SDS and, where necessary, communications are both encrypt...

We describe a deterministic model of packet delay and use it to derive both the packet pair [2] property of FIFO-queueing networks and a new technique (packet tailgating) for actively measuring link bandwidths. Compared to previously known techniques, packet tailgating usually consumes less network bandwidth, does not rely on consistent behavior of routers handling ICMP packets, and does not rely on timely delivery of acknowledgments. Preliminary empirical measurements in the Internet indicate that compared to current measurement tools, packet tailgating sends an order of magnitude fewer packets, while maintaining approximately the same accuracy. Unfortunately, for all currently available measurement tools, including our prototype implementation of packet tailgating, accuracy is low for paths longer than a few hops. 1. INTRODUCTION As long as Internet bandwidth has increased, the amount of trac sent over the Internet has grown to consume it. This means that despite the increasing li...

Accurate network bandwidth measurement is important to a variety of network applications. Unfortunately, accurate bandwidth measurement is difficult. We describe some current bandwidth measurement techniques: using throughput, pathchar [8], and Packet Pair [2]. We explain some of the problems with these techniques, including poor accuracy, poor scalability, lack of statistical robustness, poor agility in adapting to bandwidth changes, lack of flexibility in deployment, and inaccuracy when used on a variety of traffic types. Our solutions to these problems include using a packet window to adapt quickly to bandwidth changes, Receiver Only Packet Pair to combine accuracy and ease of deployment, and Potential Bandwidth Filtering to increase accuracy. Our techniques are are at least as accurate as previously used filtering algorithms, and in some situations, our techniques are more than 37% more accurate. I. INTRODUCTION A common complaint about the Internet is that it is slow. Some of this...

Abstracr- Mirror sites enable client requests to be serviced by any of a number of servers, reducing load at individual servers and dispersing network load. Typically, a client requests service from a single mirror site. We consider enabling a client to access a file from multiple mirror sites in parallel to speed up the download. To eliminate complex client-server negotiations that a straightforward implementation of this approach would require, we develop a feedback-free protocol based on erasure codes. We demonstrate that a protocol using fast Tornado codes can deliver dramatic speedups at the expense of transmitting a moderate number of additional packets into the network. Our scalable solution extends naturally to allow multiple clients to access data from multiple mirror sites simultaneously. Our approach applies naturally to wireless networks and satellite networks as well. I.

The packet pair mechanism has been shown to be a reliable method to measure the bottleneck link capacity on a network path, but its use for measuring available bandwidth is more challenging. In this paper, we use modeling, measurements, and simulations to better characterize the interaction between probing packets and the competing network traffic. We first construct a simple model to understand how competing traffic changes the probing packet gap for a single-hop network. The gap model shows that the initial probing gap is a critical parameter when using packet pairs to estimate available bandwidth. Based on this insight, we present two available bandwidth measurement techniques, the initial gap increasing (IGI) method and the packet transmission rate (PTR) method. We use extensive Internet measurements to show that these techniques estimate available bandwidth faster than existing techniques such as Pathload, with comparable accuracy. Finally, using both Internet measurements and ns simulations, we explore how the measurement accuracy of active probing is affected by factors such as the probing packet size, the length of probing packet train, and the competing traffic on links other than the tight link.

Abstract—Current Internet congestion control protocols operate independently on a per-flow basis. Recent work has demonstrated that cooperative congestion control strategies between flows can improve performance for a variety of applications, ranging from aggregated TCP transmissions to multiple-sender multicast applications. However, in order for this cooperation to be effective, one must first identify the flows that are congested at the same set of resources. In this paper, we present techniques based on loss or delay observations at end hosts to infer whether or not two flows experiencing congestion are congested at the same network resources. Our novel result is that such detection can be achieved for unicast flows, but the techniques can also be applied to multicast flows. We validate these techniques via queueing analysis, simulation, and experimentation within the Internet. In addition, we demonstrate preliminary simulation results that show that the delay-based technique can determine whether two TCP flows are congested at the same set of resources. We also propose metrics that can be used as a measure of the amount of congestion sharing between two flows. Index Terms—Hypothesis testing, inference, network congestion, queueing analysis. I.

There is an increasing need for Internet hosts to be able to quickly and efficiently learn the distance, in terms of metrics such as latency or bandwidth, between Internet hosts. For example, to select the nearest of multiple equal-content web servers. This paper explores technical issues related to the creation of a public infrastructure service to provide such information. In so doing, we suggests an architecture, called IDMaps, whereby Internet distance information is distributed over the Internet, using IP multicast groups, in the form of a virtual distance map. Systems listening to the groups can estimate the distance between any pair of IP addresses by running a spanning tree algorithm over the received distance map. We also present the results of experiments that give preliminary evidence supporting the architecture. This work thus lays the initial foundation for future work in this new area.