freenet_small - Using the Small-World Model to Improve...

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Abstract – Efficient data retrieval in a peer-to-peer system like Freenet is a challenging problem. In this paper we study the impact of cache replacement policy on the performance of Freenet. We find that, with Freenet’s LRU cache replacement, there is a steep reduction in the hit ratio with increasing load. Based on intuition from the small-world models and the recent theoretical results by Kleinberg, we propose an enhanced- clustering cache replacement scheme for use in place of LRU. Such a replacement scheme forces the routing tables to resemble neighbor relationships in a small-world acquaintance graph -- clustering with light randomness. In our simulation this new scheme improved the request hit ratio dramatically while keeping the small average hops per successful request comparable to LRU. A simple, highly idealized model of Freenet under clustering with light randomness proves that the expected message delivery time in Freenet is O( n 2 log ) if the routing tables satisfy the small-world model and have the size ) (log 2 n q . I. INTRODUCTION A peer - to - peer networked system is a collaborating group of Internet nodes which overlay their own special - purpose network on top of the Internet. Such a system performs application - level routing on top of IP routing. These systems share some of the same characteristics as the Internet in that they can grow to be quite large, may need to utilize distributed control and configuration, usually employ a naming scheme that allows them to address a node without knowing its exact whereabouts, and possess a routing mechanism that allows each node to meaningfully communicate with the rest of the system. Typically a peer - - peer network performs a very * Deptartment of Computer Science, University of Southern California, huiz@pollux.usc.edu. Part of this work was completed when the author was at Information Science Institute, University of Southern California. Research supported in part by DARPA under contract number F30602- 00-2-055. Deptartment of Computer Science and Information Science Institute, University of Southern California, agoel@pollux.usc.edu. Research supported in part by DARPA under contract number F30602-00-2-055. International Computer Science Institute, Berkeley, ramesh@ICSI.Berkeley.EDU. Part of this work was completed when the author was at Information Science Institute, University of Southern California. Research supported in part by DARPA under contract number F30602-00-2-055. specific function such as distributed data storage, cache replication, multicasting etc. and uses normal Internet functionality for all other purposes. These systems are diverse enough that it would not be desirable to make modifications to the IP routing/naming protocols to support each instance of such a system.
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This note was uploaded on 05/27/2011 for the course CIS 4930 taught by Professor Staff during the Spring '08 term at University of Florida.

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freenet_small - Using the Small-World Model to Improve...

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