Re: [Bloat] slow start: small chunks can talk
In general these papers seem quite close to a couple ideas I have been working on for a few years, and getting close to publication on. I do not know what to do about it. Soliciting input here: https://www.linkedin.com/feed/update/urn:li:activity:7092544418255171585/ On Mon, Aug 7, 2023 at 3:18 AM Sebastian Moeller wrote: > > Hi Roland. > > > On Aug 7, 2023, at 10:48, Bless, Roland (TM) via Bloat > > wrote: > > > > Hi Dave, > > > > On 01.08.23 at 00:36 Dave Taht via Bloat wrote: > >> Promising approach: > >> https://ieeexplore.ieee.org/document/10188775 > > > > It's a pity that neither the authors nor the reviewers were aware of > > earlier related work that you also sent here to the list: > > > > L. Guo and J. Y. B. Lee, "TCP-FLASH - A Fast Reacting TCP for Modern > > Networks," in IEEE Access, vol. 9, pp. 68861-68879, 2021, doi: > > 10.1109/ACCESS.2021.3077612. > > Interesting link. This still uses essentially a packet-pair measuring > method (send packet back2back, look at time difference in resulting ACK > packets to estimate bottleneck bandwidth in the forward direction). These are > still not robust or reliable... (parallel path, reordering, or simply > congestion on the reverse path, ACK filtering, ACK compression by GRO on the > receiver end, ...). Now, well possible that packet-pair data, while not > perfect, might still be good enough for the intended purpose... And even for > a traditional slow-start having an educated guess when to leave the > exponential growth phase could be helpful... > > More over, let's assume any of these (let's short circuit the probing > phase) will actually be deployed at scale; how will the network cope with the > much more aggressive ramp-up of such flows (essentially initial-window as one > batch the switch to estimated capacity once the bottleneck rate is > estimated). It is fun to see a single/few of such flows do the right thing, > but what about having the majority of flows use such methods? (Which will > likely invalidate the bottleneck rate estimate quickly). > > I guess I might be too cautious here, but I personally see the > exponential ramp-up in more traditional slow-start already as pretty > aggressive and yet more adaptive to changing capacity than jumping to the > estimated capacity essentially cold (I have similar hesitation with the > careful resume internet draft). > > Regards > Sebastian > > P.S.: "To tackle this problem, FLASH is designed to suppress > the AWnd constraint unless it is zero. This opportunistic > transmission technique, first proposed by Liu and Lee [6], > allows FLASH to send data beyond the AWnd limit up to > CWnd amount of packets inflight. " > > This is quite an euphemism "opportunistic transmission technique" for simply > ignoring parts of the protocol... > > P.P.S.: Dave's link is behind a pay-wall, so I have no idea about that paper > beyond the abstract... but if they also relay on packet-pair bandwidth > estimates and an faster-than-slow-start ramp-up, I would expect similar > issues. > > > > > > > The fast launch phase and especially the CWnd-Compensated Bandwidth > > Estimator (CCBE) are quite similar and a comparison of both approaches > > would have been interesting... > > > > Regards, > > Roland > > > > ___ > > Bloat mailing list > > Bloat@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/bloat > -- Podcast: https://www.youtube.com/watch?v=bxmoBr4cBKg Dave Täht CSO, LibreQos ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
Re: [Bloat] slow start: small chunks can talk
Hi Roland. > On Aug 7, 2023, at 10:48, Bless, Roland (TM) via Bloat > wrote: > > Hi Dave, > > On 01.08.23 at 00:36 Dave Taht via Bloat wrote: >> Promising approach: >> https://ieeexplore.ieee.org/document/10188775 > > It's a pity that neither the authors nor the reviewers were aware of earlier > related work that you also sent here to the list: > > L. Guo and J. Y. B. Lee, "TCP-FLASH - A Fast Reacting TCP for Modern > Networks," in IEEE Access, vol. 9, pp. 68861-68879, 2021, doi: > 10.1109/ACCESS.2021.3077612. Interesting link. This still uses essentially a packet-pair measuring method (send packet back2back, look at time difference in resulting ACK packets to estimate bottleneck bandwidth in the forward direction). These are still not robust or reliable... (parallel path, reordering, or simply congestion on the reverse path, ACK filtering, ACK compression by GRO on the receiver end, ...). Now, well possible that packet-pair data, while not perfect, might still be good enough for the intended purpose... And even for a traditional slow-start having an educated guess when to leave the exponential growth phase could be helpful... More over, let's assume any of these (let's short circuit the probing phase) will actually be deployed at scale; how will the network cope with the much more aggressive ramp-up of such flows (essentially initial-window as one batch the switch to estimated capacity once the bottleneck rate is estimated). It is fun to see a single/few of such flows do the right thing, but what about having the majority of flows use such methods? (Which will likely invalidate the bottleneck rate estimate quickly). I guess I might be too cautious here, but I personally see the exponential ramp-up in more traditional slow-start already as pretty aggressive and yet more adaptive to changing capacity than jumping to the estimated capacity essentially cold (I have similar hesitation with the careful resume internet draft). Regards Sebastian P.S.: "To tackle this problem, FLASH is designed to suppress the AWnd constraint unless it is zero. This opportunistic transmission technique, first proposed by Liu and Lee [6], allows FLASH to send data beyond the AWnd limit up to CWnd amount of packets inflight. " This is quite an euphemism "opportunistic transmission technique" for simply ignoring parts of the protocol... P.P.S.: Dave's link is behind a pay-wall, so I have no idea about that paper beyond the abstract... but if they also relay on packet-pair bandwidth estimates and an faster-than-slow-start ramp-up, I would expect similar issues. > > The fast launch phase and especially the CWnd-Compensated Bandwidth Estimator > (CCBE) are quite similar and a comparison of both approaches > would have been interesting... > > Regards, > Roland > > ___ > Bloat mailing list > Bloat@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
Re: [Bloat] slow start: small chunks can talk
Hi Dave, On 01.08.23 at 00:36 Dave Taht via Bloat wrote: Promising approach: https://ieeexplore.ieee.org/document/10188775 It's a pity that neither the authors nor the reviewers were aware of earlier related work that you also sent here to the list: L. Guo and J. Y. B. Lee, "TCP-FLASH - A Fast Reacting TCP for Modern Networks," in IEEE Access, vol. 9, pp. 68861-68879, 2021, doi: 10.1109/ACCESS.2021.3077612. The fast launch phase and especially the CWnd-Compensated Bandwidth Estimator (CCBE) are quite similar and a comparison of both approaches would have been interesting... Regards, Roland ___ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
