For a description of the various columns in the Figure above, please have a look at Example 1 first.

In this second example, node number 9 was already off-line before the start of the square dance exchange process (or it goes off-line during the very first exchange cycle, which is equivalent). By similar exponential spreading-out of the anomaly, column D shows that after the fifth exchange cycle, half the network finds a result of 31 accumulated contributions (which is the maximum in this case) while the other half of the network finds results in which more than just one contribution are missing, depending on their "downstream distance" to the dead node number 9.

After completion of the exchange scenario, all nodes in the top half of the table have at least one network neighbour with an accumulation result based on 31 contributions. Each node will always download the best result available, so all nodes in the top half will obtain a result based on 31 contributions, after just one repair transaction.

In each successive exchange cycle, the direct exchange partner of node 9 in that cycle (...these are the nodes 25, 1, 13, 11 and 8 respectively) will send a data request to node number 9. It will then wait for a reply - which never comes - but with a fixed time-out interval. If the end of this interval is reached, it gives up, and proceeds to the next cycle. For each of these network nodes, the overall square dance exchange scenario is therefore delayed by the duration of the time-out interval, but this also applies to all down-stream nodes, that must in turn wait for the contribution that they expect (note however that these wait-states will NOT time out: the waiting nodes will simply get a "not ready" reply from their exchange partner, and then try again after the time-out delay). The additional download for the repair cycle does not cause delays, this will take the equivalent amount of time that a nominal download from node 9 would have required. in other words: the overall square dance process is only delayed by a single time-out interval, not by multiple time-outs in sequence.

Project details

Ultimate Browsers SupportThe GPS Dancer project started in 2007 as a voluntary project of a working group of the International Association of Geodesy.

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Square dance algorithm

Great Docs and SupportThe GPS Dancer system was named after its "square dance" exchange algorithm. Of course, it also wants to to make the GPS reference frame denser.


Here, there be pirates

The Dancer on-line network became immune against internet connection problems by leaving the US marines, and becoming a pirate.

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