Re: [Bloat] Graph of bloat

[Sebastian Moeller <moeller0@gmx.de>]

Hi Hal,


On Jul 9, 2015, at 12:07 , Hal Murray <hmurray@megapathdsl.net> wrote:

> […]

> NTP makes the assumption that the network delays are symmetric.  Without bloat, that's generally reasonable.  It does screwup on long links with asymmetric routing.  If you watch NTP servers over a long distance, you can see steps when the routing changes.  On the scale of bloat, those errors are minor.  If you had a fast link rather than my slow DSL link they would be significant.
> [...]

	What about the inherent bandwidth and delay asymmetry of DSL links? The bandwidth imbalance alone can reach 10:1 and more easily (faster for ingress). And as far as I know classical reed-solomon forward error correction is most often combined with interleaving (to help against error bursts), and that interleaving often is asymmetric as well (but this asymmetry can go in both directions, so ingress might see more interleaving delay than egress. How much asymmetry can NTP cope with, and does NTP try to assess the one-way delay for both legs of the path to a server (without much thought I can fool myself into believing that if NTP would start with the symmetric connection fiction, sync the clocks and then use the synced clocks to asses the link delay asymmetry and then try to re-sync the clocks taking the just measured asymmetry into account might be a viable way around the issue; this seems simple so most likely it must be wrong ;) )?

Best Regards
	Sebastian