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

[Bob kb8tq]

Hi

One really big thing that has changed is the number of folks doing this
sort of thing via a dsl or cable modem that has > 20 ms of asymmetry. 
You will not find many NTP papers studying that sort of network connection. 

Bob

> On Dec 15, 2021, at 11:30 AM, Lux, Jim <jim at luxfamily.com> wrote:
> 
> 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.
> 
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