Monday, February 19, 2007

Object Replication Strategies in Content Distribution Networks

Jussi Kangasharju, James Roberts, Keith Ross, Computer Communication Journal, 25 (2002) 376-83.

This papers looks at the Autonomous System level distribution of content (such as Akamai content distribution network, CDN, for instance) and how to replicate the content so that, constrained on a limited memory space, the distance from the end user to the looked-for data object is minimized.

The paper shows that this is a variant of the knapsack problem and thus is NP-Complete and cannot be solved. But they provide some heuristics which show that a network wide collaboration (that is, a global management of the CDN) best all the other heuristic strategies (random, popularity-based, greedy single and greedy global). Greedy single is the strategy of replicating the content most favored by the client of each AS. Greedy global is the strategy of finding over all AS the object which replication would decrease the cost the most, and iterate until all storage space is filled.

The paper is interesting, especially since the NP-completeness of the CDN problem they consider basically includes the NP-completeness of the problem I am considering, and thus relieves me from theoretical work: all I have to do is to evaluate the proper heuristics. This also makes this paper a very easy read, as there is no equation, only the comparison of the performance of the different strategies.

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