Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc6937bis-01
Yuchung Cheng <ycheng@google.com> Thu, 04 August 2022 15:07 UTC
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From: Yuchung Cheng <ycheng@google.com>
Date: Thu, 04 Aug 2022 11:07:03 -0400
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To: Yoshifumi Nishida <nsd.ietf@gmail.com>
Cc: "tcpm@ietf.org Extensions" <tcpm@ietf.org>
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Subject: Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc6937bis-01
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To clarify, all these fixes are in https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-prr-rfc6937bis-02 My previous email was responding to Yoshifumi's question in the last tcpm meeting: did -02 address my comments? On Thu, Aug 4, 2022 at 10:00 AM Yuchung Cheng <ycheng@google.com> wrote: > > Hi Yoshifumi > > On Wed, Feb 9, 2022 at 11:30 AM Yoshifumi Nishida <nsd.ietf@gmail.com> wrote: > > > > Hi, > > > > I have the following comments on draft-ietf-tcpm-prr-rfc6937bis-01 > > > > 1: Page 5 > > "but recommended to use BBR-SSRB" > > -> PRR-SSRB? > fixed > > > > > 2: Page 7 > > "and do what? @@@@" > > -> Please add more texts or remove this. > > New text to replace the "do what" > "Without SACK, > > DeliveredData is the change in snd.una for a partial ACK or 1 MSS > worth of bytes for a DUPACK. > > Note that without SACK, a poorly-behaved receiver that returns > extraneous DUPACKs as depicted in [Savage99] can artificially inflate > DeliveredData. As a mitigation, PRR disallows incrementing > DeliveredData when the total bytes delivered exceeds the outstanding > data upon recovery (i.e., RecoverFS). > " > > > > > 3: Page 8: > > """ > > prr_delivered = 0 // Total bytes delivered during recovery > > > > prr_out = 0 // Total bytes sent during recovery > > > > """ > > -> I personally think "during recovery" might be a bit ambiguous. I think it would be better to clarify > > whether this includes a packet sent by fast retransmit or not. > > The following subroutine should be clear on that it includes retransmission > > On any data transmission or retransmission: > prr_out += (data sent) > > > > > > 4: Page 8: > > " pipe = (RFC 6675 pipe algorithm) " > > > > -> The algorithm here seems to depend on SACK, but the draft also states: > > "It is most accurate and more easily implemented with SACK [RFC2018], but does not require SACK." > > I think It is not clear how this algorithm works without SACK. > Great catch -- we define the non-SACK algorithm now in the pseudo and > clarify in section 5 > > On every ACK starting or during the recovery: > DeliveredData = bytes newly cumulatively acknowledged > if (SACK is used) { > DeliveredData += bytes newly selectively acknowledged > } else if (ACK is a DUPACK and prr_delivered < RecoverFS) { > DeliveredData += MSS > } > > > > > > 5: Section 7 Page 9 > > Why all examples shown here use Limited Transmit even though PRR doesn't require it? > > I think there should be some explanations for it even if there's no strong reason. > > We did mention that we assume RFC3042 in our section 7: "We also > assume standard Fast Retransmit and Limited Transmit [RFC3042], ... ". > We use it because it's a standard track RFC and really helps ack clocking > > > > > > > 6: Page 10: > > It seems that the pipe size in the figure is different from what RFC6675 calculates because Section 5 (4.2) in RFC6675 mentions > > " > > > > note that [RFC5681] requires that any > > segments sent as part of the Limited Transmit mechanism not > > be counted in FlightSize for the purpose of the above > > equation. > > > > > > > > Hence, I think the pipe size would be something like this if it follows RFC6675. > > > > Please let me know if I miss something. > > > > > > 6675 > > ack# X 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 > > cwnd: 20 20 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 > > pipe: 19 19 19 18 17 16 15 14 13 12 11 10 09 09 09 09 09 09 09 > > sent: N N R N N N N N N N > > > > > > PRR > > > > ack# X 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 > > pipe: 19 19 18 18 18 17 17 16 16 15 15 14 14 13 13 12 12 11 10 > > sent: N N R N N N N N N N > Thanks for catching this. Yes we've updated -bis 02 to correct the > pipe size of PRR to match RFC6675 in the initial phase of recovery. > > RFC 6675 > ack# X 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 > cwnd: 20 20 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 > pipe: 19 19 18 18 17 16 15 14 13 12 11 10 10 10 10 10 10 10 10 > sent: N N R N N N N N N N N > > > PRR > ack# X 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 > cwnd: 20 20 19 18 18 17 17 16 16 15 15 14 14 13 13 12 12 11 10 > pipe: 19 19 18 18 17 17 16 16 15 15 14 14 13 13 12 12 11 11 10 > sent: N N R N N N N N N N N > > > > > > > > > > > > 6675 > > > > ack# X X X X X X X X X X X X X X X 15 16 17 18 19 > > cwnd: 20 20 10 10 10 > > pipe: 19 19 4 10 10 > > sent: N N 6R R R > > > > > > Thanks, > > -- > > Yoshi > > > > > > > > > > _______________________________________________ > > tcpm mailing list > > tcpm@ietf.org > > https://www.ietf.org/mailman/listinfo/tcpm
- [tcpm] comments on draft-ietf-tcpm-prr-rfc6937bis… Yoshifumi Nishida
- Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc693… Yuchung Cheng
- Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc693… Yuchung Cheng
- Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc693… Yoshifumi Nishida
- Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc693… Yuchung Cheng
- Re: [tcpm] comments on draft-ietf-tcpm-prr-rfc693… Yoshifumi Nishida