Measurement times

At the DAS Cluster tests in one direction are performed, however, both an ATM and a ``usual'' Internet route is used. This implies that for n sites there are n (n - 1) roundtrip measurements, the same amount of throughput measurements and off course n machine load calculations. Due to the one-directional tests the load per site is asymmetric: site k ( $k = 1, \ldots, n$) has to do (n - k) roundtrip / throughput measurements.

The DAS Cluster consists of four sites, however, the tests across the VU - UvA connection via the ``usual'' Internet is skipped, because there is no route available. This implies that there are in total 11 roundtrip and 11 throughput measurements to be done. At each site the roundtrip measurements to the other sites are performed simultaneously, while the throughput measurements are performed serially. Using the parameters from subsection 3.1, this leads for all sites to a total roundtrip measurement time of 120 seconds and a total throughput measurement time of 110 seconds, so this gives a total measurement time of 230 seconds. The tests are performed each half an hour. There is never more than one site at a time executing the tests, so in 12.8 % of the time a site from the cluster is active with the tests.

Table 4 also shows the measurement time differentiated for each site.

 

Table: Specify the time [s] each site is busy with the network performance tests. Also the percentage active has been given. Note that the measurements are repeated each half an hour.