From: ssaponas (ssaponas@u.washington.edu)
Date: Mon Oct 11 2004 - 07:25:00 PDT
Review by T. Scott Saponas
"A Digital Fountain Approach to Reliable Distribution of Bulk Data" describes a new broadcast disk over layered multicast approach to the distribution of bulk data on the internet. Their approach's main offering over previous solutions is their use of tornado codes. These codes are like erasure codes except they are faster to encode and decode but require a larger number of source packets for full reconstruction.
The solution described in this paper is made particularly compelling by the evaluation presented. They present the results of a simulation where their tornado codes are compared with erasure codes. They show that with files of moderate size 16MB tornado codes can be computed in real-time (or very close to real time), but Reed-Solomon codes (standard implementation of erasure codes) take much longer.
I thought this paper could have been improved by some numbers motivating the need for non-unicast approaches to bulk data distribution for the scenarios they considered (ex. Downloading a new software update). To their credit, they did justify the need for new solutions where congestion control and reliability were handled without a feedback channel and where there was a very lossy channel (such as satellite distribution).
This paper does seem relevant to today's internet. It suggests some future work is to be done in figuring out schemes for mass distribution of content when the demand is so high servers would not be able to respond to the large number of requests with unicast (such as news stations like CNN on a very eventful news day).
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