Re: [Bloat] [Cerowrt-devel] FQ_Codel lwn draft article review

[Oliver Hohlfeld <oliver@net.t-labs.tu-berlin.de>]

>> iperf is a "hot rod" test. The UDP versions ignores congestion signals
>> entirely, and thus is completely irrelevant to bufferbloat.
> 
> Well I wasn't going to run it at full speed (whatever that might mean),
> but limit it to a relatively low speed, to get the jitter measurements
> for UDP in the hope they'd be a decent indication for how a voip call
> might fare on the same connection. If you have ideas for a better tool,
> I'm all ears. :)

It is not only about the tool, it is about the traffic scenario that you
have in mind. There is no such thing as "the VoIP quality". UDP jitter:
in which traffic scenario? A medium loaded backbone link? An access
link in overload? And also keep in mind that this only holds for the
absence of TCP traffic, i.e., there is only UDP traffic competing with
other UDP traffic.

Keep in mind that the relationship of jitter to VoIP quality is
complex, as it depends on the application level buffering.
There are also more impact factors other than jitter.

The jitter measurements you have in mind will give you an idea on the
jitter specific to the chosen traffic scenario, nothing more --- and in
particular not the VoIP quality (although low vs. high jitter could
/indicate/ certain /possible/ quality degradations).

--Oliver