[Codel] FQ_Codel lwn draft article review

Toke Høiland-Jørgensen toke at toke.dk
Mon Nov 26 17:16:53 EST 2012

Dave Taht <dave.taht at gmail.com> writes:

> I keep noting that the next phase of the rrul development is to find a
> good pair of CIR one way measurements that look a bit like voip.
> Either that test can get added to netperf or we use another tool, or
> we create one, and I keep hoping for recommendations from various
> people on this list. Come on, something like this exists? Anybody?

I came across this in the iperf documentation:

"Jitter calculations are continuously computed by the server, as
specified by RTP in RFC 1889. The client records a 64 bit
second/microsecond timestamp in the packet. The server computes the
relative transit time as (server's receive time - client's send time).
The client's and server's clocks do not need to be synchronized; any
difference is subtracted out in the jitter calculation. Jitter is the
smoothed mean of differences between consecutive transit times."


Iperf seems to output jitter measurements on the *server* side when
doing UDP transfers. So incorporating this into netperf-wrapper would
require either some way to notify a server to start up an iperf instance
sending to the client (and finding some way to persuade firewalls/NATs
on the way to let the packets through), or create a server-side wrapper
that monitors the server-side output and sends it to the client on
request via some sort of rpc.

The latter should be pretty straight forward, I suppose. And if I recall
correctly, you did want to measure the upstream jitter?


Toke Høiland-Jørgensen
toke at toke.dk
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