Diminished Chord: A Protocol for Heterogeneous Subgroup Formation in Peer-to-Peer Networks

David R. Karger and Matthias Ruhl

International Workshop on Peer-to-Peer Systems (IPTPS '04)
San Diego, February 2004


In most of the P2P systems developed so far, all nodes play essentially the same role. In some applications, however, different machine capabilities or owner preferences may mean that only a subset of nodes in the system should participate in offering a particular service. Arranging for each service to be supported by a different peer to peer network is, we argue here, a wasteful solution.

Instead, we propose a version of the Chord peer-to-peer protocol that allows any subset of nodes in the network to jointly offer a service without forming their own Chord ring. Our variant supports the same efficient join/leave/insert/delete operations that the subgroup would get if they did form their own separate peer to peer network, but requires significantly less resources than the separate network would.

For each subgroup of k machines, our protocol uses O(k)$ additional storage in the primal Chord ring. The insertion or deletion of a node in the subgroup and the lookup of the next node of a subgroup all require O(log n) hops.

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