Code change:
number of acknowledgments allows connection throughput to scale much further. <del> Unfortunately, there are undesirable consequences to simply reducing the acknowledgement frequency, especially to an arbitrary fixed value, as follows: A sender relies on receipt of acknowledgements to determine the amount of data in flight and to detect losses, see QUIC-RECOVERY. Consequently, how often a receiver sends acknowledgments dictates how long it takes for losses to be detected at the sender. Starting a connection up quickly without inducing excess queue is important for latency reduction, for both short and long flows. The sender often needs more frequent acknowledgments during this phase. Congestion controllers that are purely window based and strictly adherent to packet conservation, such as the one defined in QUIC- RECOVERY, rely on receipt of acknowledgments to move the congestion window forward and release additional data.  Such controllers suffer performance penalties when acknowledgements are not sent frequently enough.  On the other hand, for long-running flows, congestion controllers that are not window-based, such as BBR, can perform well with very few acknowledgements per RTT. New sender startup mechanisms will need a way for the sender to increase the frequency of acknowledgements when fine-grained feedback is required. </del> <ins> As discussed in implementation, there are undesirable consequences to congestion control and loss recovery if a receiver uniltaerally reduces the acknowledgment frequency.  Consequently, a sender needs the ability to express its constraints on the acknowledgement frequency to maximize congestion controller performance. </ins> QUIC-TRANSPORT currently specifies a simple delayed acknowledgement mechanism that a receiver can use: send an acknowledgement for every

Related discussion:
text: I think the motivations section as-is is too long. It spends a lot of time talking about what are effectively the tradeoffs. IMO the motivations section should specify why it's useful to have the sender control the receiver's ACK frequency, and then we can have a separate section for the tradeoffs. This takes a stab at that section, lifting things from motivations and adding some new text specifically addressing the nascent stages of a connection. I also made some editorial changes to the existing text. I am happy to add any additional considerations we think might need to be called out. This attempts to
Thanks for the PR, NAME ! I like the new text you propose (I've proposed some changes), but I think you might be assuming that ACK_FREQUENCY is only used for delaying acks further. An important point that bears bringing out in the motivation is that a sender might want more frequent acks as well, for example during startup. That's worth capturing in the modified motivation section.
NAME this PR is almost done, any chance you can do another round of updates and we can get it in?
NAME sorry, I'll do some updates today.
NAME NAME I've updated the PR, I'll watch and iterate on any remaining feedback quickly this time.
thanks NAME Something about vim and the macbook pro keyboard apparently makes me incapable of spelling things properly. I want my desk keyboard back
As discussed on in the base draft, we have some confidence in a particular heuristic (default tolerance of 2 for the first 100 packets, followed by a tolerance of 10) which we know to work fairly well in multiple deployments serving "typical" Internet resources to typical users. Do we want to make that recommendation explicit, or otherwise give guidance in this extension?
I think it's a good idea to describe the values for which we have experience, while encouraging experimentation. We don't need to recommend the strategy, we just need to document it as an example strategy.
I think a section on considerations and maybe past experience would be very helpful. I think it's going to be a bit of a challenge to write, but I'm happy to take a stab if no one else wants to.
What I'd want to see is just a simple explanation of what a sender could do... I would not describe results from experience, since those are anecdotal and are going to change over time. This could be a fairly short section.