Fault Tolerant Active Rings for Structured Peer-to-Peer Overlays

Abstract

Algorithms by which peers join and leave structured overlay networks can be classified as passive or active. Passive topology maintenance relies on periodic background repair of neighbor pointers. When a node passively leaves the overlay, subsequent lookups may fail silently. Active maintenance has been proven only for fault-free networks. We develop an active topology maintenance algorithm for practical, fault-prone networks. Unlike prior work, it a) maintains ring continuity during normal topology changes and b) guarantees consistency and progress in the presence of faults. The latter property is inherited by novel extension of the Paxos Commit algorithm. The topology maintenance algorithm is formally developed using the B Method and its event-driven extensions for dynamic systems. Messaging and storage overheads are quantified.

Concurrent Maintenance of Rings

“…How to handle faults is clearly an important research problem. In fact, subsequent to the original announcement of the results in this paper [11], other researchers have leveraged our work for the design and verification of a fault-tolerant active ring maintenance protocol [22].…”

Survey of research towards robust peer-to-peer networks: Search methods

“…Lynch and Stoica show in an enhancement to Chord that lookups are provably correct when there is a limited rate of joins and failures [282]. Fault Tolerant Active Rings is a protocol for active joins and leaves that was formally specified and proven using B-method tools [283]. A good starting point for a formal DHT development would be the numerous informal API specifications [22,284,285].…”

Maintaining the Ranch topology

“…Risson et al [39] extend our previous work [25] to the design and verification of a fault-tolerant active ring maintenance protocol. The main idea is to treat every join or leave operation as a transaction, which is controlled by a Paxos commit algorithm.…”