Re: [quicwg/base-drafts] Explicit support for on-path calculation of loss and congestion of QUIC flows (#632)

[Brian Trammell <[e-mail]>]

Loss measurement is currently useful in a couple of network troubleshooting and capacity planning tasks: isolating congested links (and upgrading or shifting load away from them), as well as differentiating actual loss at the link layer from congestion (and repairing lossy links). It is useful to measure these conditions both on one's own network (where you can repair them yourself) as well as isolating them to some upstream or downstream path on other networks (so you can work to shift traffic away from those networks).

Universal deployment of useful AQM + ECN would both reduce the absolute magnitude of the congestion problem as well as make loss and congestion easily distinguishable. I'm optimistic about the time horizon here, but it's still measured on the order of decades.

You're right that the inference-based method, assuming that flight size reduction is loss- or congestion-signal related, is not a very high-fidelity signal, and may be useless depending on how the sender does transmission scheduling. So if we're serious about supporting this, I think we do need to take a good look at the ConEx mechanism and see if there's a low-overhead way to support it in QUIC.

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