Code was inserted in the POP server program to generate log entries for each connection. The length of time that it takes the client to connect to the server and present the id and password is not recorded, so significant delays in resolving DNS entries or establishing a TCP connection will not be measured. The time stamps of the recorded log entries are to a resolution of a second. A lot of the times being measured are sub-second and accurate measurements are dependent on obtaining lots of samples and computing ratios of those transactions which begin and end in the same time interval vs those which begin in one and end in another, either because the transaction begins towards the end of a second or because the transaction is somewhat longer than usual. The author was strongly reminded of the behaviour of waves while studying the data obtained from the logs.
Waves move across a medium with a speed that is a function of wavelength.
As faster waves catch up with slower waves, they interfere in an alternative destructive and constructive manner, thus the medium will temporarily calm then apparently out of nowhere a wave with the combined height will form. Thus out of an ocean with average waves of 30 meters one can observe a wave of 90 or more meters forming lasting a few minutes then separating back out into the component waves. When such a wave forms under a tanker, a disaster can occur. Similarly in the patterns of access to the POP server, we see wave like patterns occurring. Different people configure their clients to check for new mail at different rates in the same way that waves move at different speeds.