REVIEW: "Chord: A Scalable Peer-to-Peer Lookup Protocol for Internet Applications"

REVIEW: "Chord: A Scalable Peer-to-Peer Lookup Protocol for Internet
Applications"

The paper presents Chord a distributed protocol for content lookup in
peer-to-peer applications. Chord maps keys to hosts in the network and can
thus be used to assign values to nodes and locate this information based
on unique keys associated with the values. The paper also shows proofs of
Chord's correctness and provides simulation results which demonstrate its
robustness and performance under node failures.

Simulation results presented demonstrate that Chord adapts well to nodes
joining and leaving the system and is able to answer queries even if the
systems is continuously changing. Nodes joining and leaving cause only few
timouts and lookup failures in queries as Chord is able to provide robust
correctness even when some information in nodes may be outdated.

The paper also shows that Chord supports joins and failures with little
overheads, requiring that at most O(1/N) fraction of keys need to be
moved. It is also shown to be scalable as the communication costs and
state maintained by each node increase only logarithmically O(logN) with
number of nodes in the system.

By distributing keys well through hosts, Chord provides effective load
balancing which is futher improved with added virtual nodes as an
indirection layer.

Although the paper points out Chord's shortcomings relative to other
existing systems, it fails to assess its impact. For example, the fact
that Chord fails to explore network locality results in higher latencies
than necessary which make it impractical for lookups in worldwide
peer-to-peer networks. Applications which use Chord, must then implement
locality awareness on top of chord by mirroring content at different
locations.
Received on Mon Nov 07 2005 - 02:02:35 EST