[e2e] Latency Variation and Contention.

Joe Touch touch at ISI.EDU
Wed Aug 17 07:34:08 PDT 2005

Sireen Habib Malik wrote:
> Hi,
>>>what you are aiming at is SNR, i.e., 10log10(RTT/dRTT)
> So we are getting somewhere now :-)
> Right. SNR is the signal strength normalized to the noise strength. For
> dRTT=0, SNR=f(RTT/dRTT)=infinite.
> I considered "congestion" as the noise strength normalized to the signal
> strength. For dRTT=0, congestion signal based upon dRTT/RTT=
> f(dRTT/RTT)= zero = no congestion.

You can consider it the noise ratio, but why? There are other reasons
that RTT can vary - multipath routing, in particular.

All SNR does here is tell you how noisy the RTT is, which tells you how
good you can run your feedback control (which is RTT-dependent). It
doesn't tell you whether there is congestion, though. There may be a
correlation in some systems, but it's not cause-effect. There are too
many other causes for noisy RTTs.

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