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

[Philip Prindeville <[e-mail]>]

> On Apr 17, 2020, at 4:48 AM, Harlan Stenn <[e-mail]> wrote:
> 
> [snip]
> 
> More to the point, NTPv4 and all of its predecessors specified:
> 
> - the packet format
> - the algorithms
> - a set of behavioral limits and specifications
> 
> This means others were allowed to write specifications (regulations)
> assuming and/or relying on "NTP" - the packet format, algorithms, and
> behavior.
> 
> Removing or separating the algorithmic and behavioral specifications
> from the NTP specification at best cost-shifts that discussion
> elsewhere, and I submit it does this to groups that are likely
> completely unaware that they can no longer rely on behavior that they
> had no idea they previously relied on.
> 
> Are you planning to just do a protocol spec and "do the algorithms and
> behavior spec later", or worse yet, let others do that if they think
> it's important?


Not to throw gasoline on the fire, but Postel told me decades ago, “don’t confuse protocol and policy” (he was [ahem] encouraging me to drop 3 paragraphs from the draft of RFC 1048).  It was good advice then and it holds.

Algorithms are, in essence, a “policy” for disciplining a clock.

A compromise might be to define requirements for the protocol parametrically, in terms of drift, jitter, etc. while not defining the algorithms to do that.

This opens the field up to more active research in ways to improve the protocol and the use of clocks without tying anyone’s hands.

The protocol could provide a “reference algorithm” that’s used as a baseline and as an example of a certain performance “envelope” under well-defined circumstances.

Given how long NTPv4 has been around (for both right and wrong reasons), it’s reasonable to expect NTPv5 to live at least half as long.  A lot of technology can potentially emerge during that time and we should have the flexibility to incorporate it as it develops.

Look how far we’ve come since Cesium ovens as reference clocks.

-Philip