tailieunhanh - Chord: A Scalable Peer-to-peer Lookup Protocol for Internet Applications

Peer-to-peer systems and applications are distributed systems without any centralized control or hierarchical organization, in which each node runs software with equivalent 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,. | Chord A Scalable Peer-to-peer Lookup Protocol for Internet Applications Ion Stoicay Robert Morrisz David Liben-Nowellz David R. Karger M. Frans Kaashoekz Frank Dabekz Hari Balakrishnan Abstract 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. I. Introduction Peer-to-peer systems and applications are distributed systems without any centralized control or hierarchical organization in which each node runs software with equivalent 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 consistent hashing 12 to assign keys to Chord nodes. Consistent hashing tends to balance load since each node receives roughly the same number of