[tor-relays] Traffic pattern on Tor relay

Hi,

I am monitoring the network interface of my tor server with nload. From time to time nload shows strange traffic patterns: http://i.imgur.com/0Wr9h.png

The graph is updated every second so one hash mark corresponds to one second. The most recent traffic value is on the right side. The graph shows that the traffic oscillates with a period of about 14 seconds and the traffic doubles in the peaks.

Does anyone has an explanation of this pattern?

Regards,

Torland