Frank Dabek

Chord: a scalable peer-to-peer lookup protocol for Internet applications

A fundamental problem that confronts peer-to-peer applications is the efficient location of the node that stores a desired data item. This paper presents Chord, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis and simulations show that Chord is scalable: Communication cost and the state maintained by each node scale logarithmically with the number of Chord nodes.

Vivaldi: a decentralized network coordinate system

Large-scale Internet applications can benefit from an ability to predict round-trip times to other hosts without having to contact them first. Explicit measurements are often unattractive because the cost of measurement can outweigh the benefits of exploiting proximity information. Vivaldi is a simple, light-weight algorithm that assigns synthetic coordinates to hosts such that the distance between the coordinates of two hosts accurately predicts the communication latency between the hosts. Vivaldi is fully distributed, requiring no fixed network infrastructure and no distinguished hosts. It is also efficient: a new host can compute good coordinates for itself after collecting latency information from only a few other hosts. Because it requires little com-munication, Vivaldi can piggy-back on the communication patterns of the application using it and scale to a large number of hosts. An evaluation of Vivaldi using a simulated network whose latencies are based on measurements among 1740 Internet hosts shows that a 2-dimensional Euclidean model with height vectors embeds these hosts with low error (the median relative error in round-trip time prediction is 11 percent).

Towards a Common API for Structured Peer-to-Peer Overlays

In this paper, we describe an ongoing effort to define common APIs for structured peer-to-peer overlays and the key abstractions that can be built on them. In doing so, we hope to facilitate independent innovation in overlay protocols, services, and applications, to allow direct experimental comparisons, and to encourage application development by third parties. We provide a snapshot of our efforts and discuss open problems in an effort to solicit feedback from the research community.

Building peer-to-peer systems with chord, a distributed lookup service

We argue that the core problem facing peer-to-peer Systems is locating documents in a decentralized network and propose Chord, a distributed lookup primitive. Chord provides an efficient method of locating documents while placing few constraints on the applications that use it. As proof that Chords functionality is useful in the development of peer-to-peer applications, we outline the implementation of a peer-to-peer file sharing system based on Chord.

Event-driven programming for robust software

Events are a better means of managing I/O concurrency in server software than threads: events help avoid bugs caused by the unnecessary CPU concurrency introduced by threads. Event-based programs also tend to have more stable performance under heavy load than threaded programs. We argue that our libasync non-blocking I/O library makes event-based programming convenient and evaluate extensions to the library that allow event-based programs to take advantage of multi-processors. We conclude that events provide all the benefits of threads, with substantially less complexity; the result is more robust software.

UsenetDHT: a low overhead usenet server

UsenetDHT is a system that reduces the storage and bandwidth resources required to run a Usenet server by spreading the burden of data storage across participants. UsenetDHT distributes data using a distributed hash table. The amount of data that must be stored on each node participating in UsenetDHT scales inversely with the number of participating nodes. Each node’s bandwidth requirements are proportional to the fraction of articles read rather than to the total number posted.