Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04: flipped exponents in the AVG_W_cubic formulas?
"Black, David" <David.Black@dell.com> Fri, 03 September 2021 18:19 UTC
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From: "Black, David" <David.Black@dell.com>
To: Neal Cardwell <ncardwell=40google.com@dmarc.ietf.org>, "draft-ietf-tcpm-rfc8312bis@ietf.org" <draft-ietf-tcpm-rfc8312bis@ietf.org>
CC: tsvwg IETF list <tsvwg@ietf.org>, "tcpm@ietf.org" <tcpm@ietf.org>, "Black, David" <David.Black@dell.com>
Thread-Topic: [tsvwg] draft-ietf-tcpm-rfc8312bis-04: flipped exponents in the AVG_W_cubic formulas?
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/ObgshX5PWlM71GtTkzGPrlWYxUI>
Subject: Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04: flipped exponents in the AVG_W_cubic formulas?
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+tcpm list, Thanks, --David From: tsvwg <tsvwg-bounces@ietf.org> On Behalf Of Neal Cardwell Sent: Friday, September 3, 2021 2:01 PM To: draft-ietf-tcpm-rfc8312bis@ietf.org Cc: tsvwg IETF list Subject: [tsvwg] draft-ietf-tcpm-rfc8312bis-04: flipped exponents in the AVG_W_cubic formulas? [EXTERNAL EMAIL] Dear rfc8312bis authors, First, thanks for all your work on rfc8312bis! Next: I was about to use the AVG_W_cubic formulas in the rfc8312bis text, and noticed what appears to be a discrepancy between the rfc8312bis AVG_W_cubic formulas and the AVG_W_cubic formulas in both: (1) the RFC 8312: https://datatracker.ietf.org/doc/html/rfc8312#section-5 [datatracker.ietf.org]<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/rfc8312*section-5__;Iw!!LpKI!welVSQZsssTZQj9y8Cm-amEp4qNGzHvB78GbqqIy54xLFYKtqVkmuUpzvGuHwrVI$> (2) the CUBIC paper: https://dl.acm.org/doi/10.1145/1400097.1400105 [dl.acm.org]<https://urldefense.com/v3/__https:/dl.acm.org/doi/10.1145/1400097.1400105__;!!LpKI!welVSQZsssTZQj9y8Cm-amEp4qNGzHvB78GbqqIy54xLFYKtqVkmuUpzvJFEothA$> In both (1) and (2) the formulas have RTT and p taken to the power of 3/4; for example: With beta_cubic set to 0.7, the above formula is reduced to: AVG_W_cubic = (C*3.7/1.2)^0.25 * (RTT^0.75) / (p^0.75) (Eq. 6) By contrast, the rfc8312bis text, in Figures 5, 6, and 7, has RTT and p taken to the power of 4/3: ________________ ____ /C * (3 + β ) 3 / 4 4 / cubic |/ RTT AVG_W = | / ---------------- * ------- cubic | / 4 * (1 - β ) __ |/ cubic 3 / 4 |/ p Figure 5 ---- ____ _______ 3 / 4 4 /C * 3.7 |/ RTT AVG_W = | / ------- * ------- cubic |/ 1.2 __ 3 / 4 |/ p Figure 6 ---- 3 / 4 |/ RTT AVG_W = 1.054 * ------- cubic __ 3 / 4 |/ p Figure 7 That is, it appears there are typos in the formulas in rfc8312bis that systematically swapped the 3 and 4 in the exponents for RTT and p, yielding exponents of 4/3 instead of the 3/4 value from the original paper and RFC 8312. best regards, neal
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Black, David
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Bob Briscoe
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Lars Eggert
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Rodney W. Grimes
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Lars Eggert
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Rodney W. Grimes
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… tom petch
- Re: [tcpm] [tsvwg] draft-ietf-tcpm-rfc8312bis-04:… Bob Briscoe