Hybrid Overlay Structure Based on Random Walks

To overcome problems of DHT: difficult to adapt to topology chagnes. Does not consider node heterogeneity.
Nodes form clusters with DHT. Every cluster elect a super node called 'root'. Roots of all clusters form core net with DHT. In addition, clusters also connect with random links. Random links can hash to nodes inside the cluster with DHT. Routing can pass to root and operate on core, or by random links.

Arpeggio: Metadata Searching and content sharing with Chord

Support for complex query in DHT.KSS (Keyword-Set Searching) system. Allow precompute the full index answer to all queries of up to k-keywords. Metadata Expiration, instead of polling for economic reason. Index Gateway, instead of publish a file's metata to DHT nodes, publish to gateway, and gateway register to DHT. So avoid multiple publish to DHT.