[Cake] A few puzzling Cake results

Toke Høiland-Jørgensen toke at toke.dk
Tue Apr 17 05:42:50 EDT 2018

I've been trying to show the benefit of Cake's diffserv mode and came
across a few odd results along the way. Attached are two plots of a test
run with 32 TCP flows competing with a single EF-marked VoIP flow.

The puzzling points are:

- There is not difference between Cake in diffserv mode and non-diffserv
  mode. For FQ-CoDel, 32 flows (on a 10Mbit link) are clearly too many
  to keep the VoIP flow prioritised through the sparse flow
  optimisation. This is to be expected. However, Cake (in besteffort
  mode) does not show this tendency. Why not?

- The TCP RTT of the 32 flows is *way* higher for Cake. FQ-CoDel
  controls TCP flow latency to around 65 ms, while for Cake it is all
  the way up around the 180ms mark. Is the Codel version in Cake too
  lenient, or what is going on here?


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