Re: Call For Adoption QUIC: delayed-ack

[Mirja Kuehlewind <[e-mail]>]

Hi Matt,

your description below does not mention min_ack_delay and that's the part I was wondering about. The implementation as you explained below is also what I would expect but it less clear to me what to do with the values provided by min_ack_delay.

Mirja


On 07.04.21, 21:00, "Matt Joras" <[e-mail]> wrote:

    Hi Mirja,

    Below is my interpretation though since we are having this discussion
    perhaps this needs to be made clearer in the text.

    On Wed, Apr 7, 2021 at 10:06 AM Mirja Kuehlewind
    <[e-mail]> wrote:
    >
    > Hi Ian,
    >
    >
    >
    > see blow.
    >
    >
    >
    > From: Ian Swett <ianswett=[e-mail]>
    > Date: Wednesday, 7. April 2021 at 18:59
    > To: Mirja Kuehlewind <[e-mail]>
    > Cc: Matt Joras <[e-mail]>, IETF QUIC WG <[e-mail]>
    > Subject: Re: Call For Adoption QUIC: delayed-ack
    >
    >
    >
    > Hi Mirja,
    >
    >
    >
    > min_ack_delay is used to limit the minimum ack delay you can request in the ACK_FREQUENCY frame: "Any value smaller than the "min_ack_delay" advertised by this endpoint is invalid."  https://tools.ietf.org/html/draft-iyengar-quic-delayed-ack-02#section-4. After re-reading, possibly "this endpoint" is not specific enough?
    >
    >
    >
    > I was missing further guidance on how to implement that. Usually if I have a packet tolerance of e.g. 2, I would just ack every other packet. Am I supposed to delay my ack if the last was ACK was send to close by? Would I need to use the delayed ACK timer for that or a separate timer? Didn’t think that through but thought it would be good to have more guidance in the draft.
    >

    The ACK_FREQUENCY frame essentially just gives a sender a mechanism to
    alter the otherwise hard coded behavior of the receiver and otherwise
    does nothing to change the logic. In QUIC we have 3 things which can
    affect ACK frequency :
    1. "packet tolerance" (I really wish we could come up with a better
    term for this), which is defaulted to two, or every other packet.
    2. Max ack delay, settable with a default of 25ms.
    3. Out of order packets, via a threshold

    An ACK is supposed to be sent when any of the above conditions are
    met. The same is true when using the ACK_FREQUENCY frame, except that
    the conditions can change during a connection. The packet tolerance
    and max ACK delay are dynamic instead of static, so the logic should
    be identical except for allowing these values to change. The out of
    order packets behavior is also controllable in a binary fashion,
    effectively removing the condition entirely.
    >
    > Mirja
    >
    >
    >
    >
    >
    >
    >
    >
    >
    > 2) I filed https://protect2.fireeye.com/v1/url?k=826ab963-ddf18063-826af9f8-86fc6812c361-c26453d8be9cda19&q=1&e=28123d83-0cab-4534-b339-c4c176ece256&u=https%3A%2F%2Fgithub.com%2Fjanaiyengar%2Fack-frequency%2Fissues%2F48 for this.
    >
    >
    >
    > Thanks for reading, Ian
    >
    >
    >
    > On Wed, Apr 7, 2021 at 9:56 AM Mirja Kuehlewind <mirja.kuehlewind=[e-mail]> wrote:
    >
    > Hi,
    >
    > I know I'm too late but I also support adoption.
    >
    > But now that I found the time to read the draft again, I also have two comment:
    >
    > 1) It seems like min_ack_delay is "only" used for negotiation because the draft does not specify any further what to do with this value. Isn't either min_ack_delay or Packet Tolerance sufficient, e.g. what if you have a packet tolerance of 1 but a min_ack_delay of > 0?
    >
    > 2) For ECN, you don't need to send an immediate ACK for each CE. Immediate ACKs are most important when the codepoint switches to CE, but then, if multiple CEs in a row are received, you can bundle the ACK information. See also https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-14#section-3.2.2.5.1
    > (Note that we are still working on that section for AccECN but I think any changes are only relevant for specifics of TCP)
    >
    > Mirja
    >
    >
    >
    > On 30.03.21, 21:39, "QUIC on behalf of Matt Joras" <[e-mail] on behalf of [e-mail]> wrote:
    >
    >     Hello all,
    >
    >     Now that we have been rechartered we can move forward with adopting
    >     new items. It is the opinion of the chairs that the delayed-ack
    >     draft[1] has sufficient interest from and relevance to the WG to be
    >     formally adopted. This email is the call to do so. There are already
    >     several interoperating implementations of the current draft. Please
    >     reply to this email with any comments, the call will run through April
    >     6th.
    >
    >     Thanks,
    >     QUIC Chairs
    >
    >     [1] https://datatracker.ietf.org/doc/draft-iyengar-quic-delayed-ack/
    >

    Matt Joras