[time-nuts] Re: NIST NTP servers way off for anyone else?

[Lux, Jim]

On 12/15/21 7:53 AM, Magnus Danielson via time-nuts wrote:
> Hi,
>
> Expect network routes to be more dispersed these days, as it is needed.
>
> While the wedge plot is a classic for NTP, it may be interesting to 
> plot forward and backward path histograms independently.
>
> Cheers,
> Magnus 


I assume someone, somewhere has run some recent tests and maybe 
published them. All those plots and behaviors from the early days of NTP 
might have significantly changed, due to the plethora of new kinds of 
network routes.  Two things strike me as being "very different" from, 
say, 10-20 years ago - 20 years ago, most routers were "store and 
forward" - the entire packet would be received, and then decoded, and 
sent onward.  These days, many routers start sending the packet to the 
destination before the entire packet has been received.  To do S&F would 
take too much memory with multi Gbps speeds and long packets.  I recall 
being at a conference at least 10 years ago where they were talking 
about the sophistication required in 10G routers - cut through routing, 
adaptive equalization, etc.

The other thing that has changed is a modern diversity of kinds of 
networks. 20 years ago, it was basically wired connections of some kind 
with concentrators/deconcentrators/switches/routers - all of which have 
moderately well defined latency and statistics.

Now, though, there's a lot of over the air (cell phones, WISP, 5,6,7G 
nanocells injected surreptitiously - at least my neighbor claims that's 
what they're doing).  The latency on a WiFi connection, in a busy 
environment - It's 8PM, and all the neighbors are streaming "The Wheel 
of Time" (appropriately, for time-nuts) - varies wildly over a short 
time. (I will say that WiFi latency improves dramatically during a power 
failure in a residential neighborhood when you have backup power, and 
your neighbors do not)

Imagine NTP running over Starlink, especially when there are multi hop 
crosslinks between satellites.  At 7 km/s orbital velocity, the range is 
changing as much as 21 microseconds/second to a "stationary" observer.  
Now consider two satellites in different orbital planes. The dynamics of 
the latency get quite complex.