Re: [Ntp] The bump, or why NTP v5 must specify impulse response

[Daniel Franke <[e-mail]>]

On Sun, Apr 12, 2020 at 6:11 PM Watson Ladd <[e-mail]> wrote:
> Section 14.5 of Phase Lock Techniques by Floyd Gardner describes
> difficult problems caused by the accumulation of errors in a chain of
> PLLs under benign conditions, and section 2.2.4 describes the root
> cause, namely an inevitable peak in the transfer function of a second
> order filter. I don't think these are insolvable in NTP v5, but they
> should give pause to the idea that we can avoid needing to specify the
> the synchronization algorithm. The peaking of the PLL needs to be
> controlled, or some thing more complex needs to be specified.

Are the algorithms in RFC 5905 vulnerable to this? If so, I think that
shoots down any implication that it's a practical necessity to solve
this in the NTPv5 spec, since we've obviously been getting by okay so
far.

Just to be clear, though, I'm not proposing that the WG should be
*silent* on synchronization algorithms in v5. Just that whatever we
have to say about it should be in a separate, Informational document,
and can discuss the design space and suggest multiple possibilities
rather than require one particular thing.