Subject: 1-bit spin bit; some results

From: Marcus Ihlar <[email-masked]>
Date: Wed, 18 Jul 2018 19:09:39 +0000

Hi,

We have done measurements to test the impact of different kinds of network impairments has on the spin bit signal. The results we have so far are very promising in terms of how useful the mechanism is.

Short summary:
The spin bit works well and provides good RTT estimates. Use of simple heuristics in the measurement node makes the RTT measurements robust to severe levels of reordering.

Observations:

Downstream impairments have little or no impact on the spin bit signal. This is fairly obvious as the flow is well ordered at the observation point.

Severe reordering has the most negative impact on the spin bit signal quality since there is scrambling along the edges. Simple heuristics can be applied to minimize the reordering impact.

Random packet loss has a very small impact on the spin bit signal, a slight bias towards larger RTT samples (compared to ideal measurements) is observed.

We also looked at the sample frequency of the spin bit signal (1 sample per RTT) and compared it with the higher frequency sampling at the server (1 sample per ACK). The server has a slight bias towards smaller samples, but the difference is negligible.

We find these results very encouraging so far and will continue to scale up and do further measurements.

There wasn't time enough at the QUIC session in Montreal to present the results, but you can find the slides here:

https://github.com/quicwg/wg-materials/blob/master/ietf102/SPIN-QUICWG.pdf

/Marcus Ihlar

<https://github.com/quicwg/wg-materials/blob/master/ietf102/SPIN-QUICWG.pdf>

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