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6.1 Refining Azureus' Coordinates

Because updates to the CVS tree could take weeks to proliferate to a majority of users, changing single variables or techniques was not feasible. Instead we relied on simulations and on-going measurement to guide the roll-out of two major coordinate versions.

Azureus' coordinates originally used two dimensions, height, and none of the three filtering techniques we described in Section 4. We call this version 2D+H. To create version 5D, we incorporated the two techniques from our previous research, latency and update filters, into the code. Based on our on-going PlanetLab coordinate service, which did not use height and reliably exhibited low error, we also dropped height and added three more dimensions. Unfortunately, removing height proved to be a mistake. Through simulations of the Azureus latency matrix (see Figure 6), we realized we could expect a substantial improvement in accuracy by converting the last dimension of the 5d implementation to height without changing the gossip packet structure. We also found the highly skewed neighbor sets slowed convergence and developed the neighbor decay technique to compensate. We combined these changes and rolled out version 4D+H.

Figure 6: Because height had a major, positive impact on Azureus in simulation, we returned it to the 4d+h version.

   
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