TAILIEUCHUNG - Chord: A Scalable Peertopeer Lookup Service for Internet Applications

Previous work on consistent hashing assumed that nodes were aware of most other nodes in the system, making it impractical to scale to large number of nodes. In contrast, each Chord node needs “routing” information about only a few other nodes. Because the routing table is distributed, a node resolves the hash function by communicating with a few other nodes. In the steady state, in an -node system, each node maintains information only about other nodes, and resolves all lookups via messages to other nodes. Chord maintains its routing information as nodes join and leave the system; with high probability each such event results in no more than . | Chord A Scalable Peer-to-peer Lookup Service for Internet Applications Ion Stoica Robert Morris David Karger M. Frans Kaashoek Hari Balakrishnan1 MIT Laboratory for Computer Science chord@ http chord Abstract A fundamental problem that confronts peer-to-peer applications is to efficiently locate the node that stores a particular 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 item 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 simulations and experiments show that Chord is scalable with communication cost and the state maintained by each node scaling logarithmically with the number of Chord nodes. 1. Introduction Peer-to-peer systems and applications are distributed systems without any centralized control or hierarchical organization where the software running at each node is equivalent in functionality. A review of the features of recent peer-to-peer applications yields a long list redundant storage permanence selection of nearby servers anonymity search authentication and hierarchical naming. Despite this rich set of features the core operation in most peer-to-peer systems is efficient location of data items. The contribution of this paper is a scalable protocol for lookup in a dynamic peer-to-peer system with frequent node arrivals and departures. The Chord protocol supports just one operation given a key it maps the key onto a node. Depending on the application using Chord that node might be responsible for storing a value associated with the key. Chord uses a variant of consistent hashing 11 to assign keys to Chord nodes. .

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