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The packet trace facility is able to coordinate measurements between the different machines. One machine will trigger the other
machine by setting a flag in the header of outgoing packets to start tracing the same range of packets that it is tracing. The other
machine will in turn trace all packets that it sees with the same header flag set. This coordination ensures that the information about
the same packets is stored at each end of the connection regardless of what happens in between.
The user level trace analyzer is the other level in the WREN environment. It is the component that begins any packet traces and
collects and processes the data returned from the kernel level trace facility. By design the user-level components are not required to
read the information from the packet trace facility at all times. It can be analyzed immediately after the trace is completed to make
runtime decisions or stored for future analysis.
When traffic is low, WREN will actively introduce traffic into the network in order to maintain a continuous flow of measurements.
After numerous studies, it was found that WREN produced the same measurements in congested and un-congested environments
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