Overlay Networks Internet routing has exhibited scalability Internet
Overlay Networks + Internet routing has exhibited scalability - Internet routing is inefficient - Difficult to add intelligence to Internet Solution: Overlay networks (U. Washington, MIT)
Research Topic: Scalability Issues • Complete virtual networks scale poorly • MIT RON scales to about 50 or so nodes • Primary challenge: overlay networks are modeled as a complete graph; Each node need to disperse O(n) information to O(n) neighbors resulting in O(n 3) traffic • Solution: build sub-graphs • Each node picks some random links (used in Yoid) + distributed algorithm - does not necessarily pick the good links • Each node picks a few good links coming out of it (used in Narada) + distributed algorithm - does not guarantee connectivity! • Graph theoretic algorithms by Roskind-Tarjan, Gabow + good approximate solutions to an NP-Complete problem - centralized algorithm • Our approach: distributed, approximation to Roskind-Tarjan Real implementation on Planetlab nodes
Research Topic: Overlay Network Applications • Coherent wide-area file systems (and object location mechanisms) on top of overlay networks • Differs from existing object location schemes (which are based on distributed hash tables) in following ways: • • • Provide mutable object semantics Provide different kinds of consistency Make the system “self-synchronizing” Meta-data (location information) needs to be persistent Need to exploit topology
Other research topics • Evaluate mobile storage alternatives: • What is the best file system for different storage technologies? • File systems: unix file system, log-structure file system, and other variants • Technologies: microdrives, compact flash, storage accessed through wireless • Build a distributed file system for mobile devices • Data exists at different locations with different kinds of connectivity • At one extreme: can have disconnected operation • Try to access the most accessible copy, try to minimize the amount of communication overhead to maintain consistency
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