Hierarchical peer-to-peer systems

Structured peer-to-peer (P2P) lookup services organize peers into a
flat overlay network and offer distributed hash table (DHT) functionality. Data
is associated with keys and each peer is responsible for a subset of the keys. In
hierarchical DHTs, peers are organized into groups, and each group has its autonomous
intra-group overlay network and lookup service. Groups are organized
in a top-level overlay network. To find a peer that is responsible for a key, the
top-level overlay first determines the group responsible for the key; the responsible
group then uses its intra-group overlay to determine the specific peer that is
responsible for the key.We provide a general framework and a scalable hierarchical
overlay management. We study a two-tier hierarchy using Chord for the top
level. Our analysis shows that by using the most reliable peers in the top level,
the hierarchical design significantly reduces the expected number of hops.