[semenko]

I found the most interesting part of the NIST outage post [1] is NIST's special Time Over Fiber (TOF) program [2] that "provides high-precision time transfer by other service arrangements; some direct fiber-optic links were affected and users will be contacted separately."

I've never heard of this! Very cool service, presumably for … quant / HFT / finance firms (maybe for compliance with FINRA Rule 4590 [3])? Telecom providers synchronizing 5G clocks for time-division duplexing [4]? Google/hyperscalers as input to Spanner or other global databases?

Seriously fascinating to me -- who would be a commercial consumer of NIST TOF?

[1] https://groups.google.com/a/list.nist.gov/g/internet-time-se...

[2] https://www.nist.gov/pml/time-and-frequency-division/time-se...

[3] https://www.finra.org/rules-guidance/rulebooks/finra-rules/4...

[4] https://www.ericsson.com/en/blog/2019/8/what-you-need-to-kno...

[dmurray]

I never saw a need for this in HFT. In my experience, GPS was used instead, but there was never any critical need for microsecond accuracy in live systems. Sub-microsecond latency, yes, but when that mattered it was in order to do something as soon as possible rather than as close as possible to Wall Clock Time X.

Still useful for post-trade analysis; perhaps you can determine that a competitor now has a faster connection than you.

The regulatory requirement you linked (and other typical requirements from regulators) allows a tolerance of one second, so it doesn't call for this kind of technology.

[blibble]

> I never saw a need for this in HFT. In my experience, GPS was used instead, but there was never any critical need for microsecond accuracy in live systems.

mifid ii (uk/eu) minimum is 1us granularity

https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv:...

[goalieca]

My guess would be scientific experiments where they need to correlate or sequence data over large regions. Things like correlating gravitational waves with radio signals and gamma ray bursts.

[prpl]

those are GPS based too. You typically would have a circuit you trained off off 1PPS and hopefully had a 10 or so satellites in view.

You can get 50ns with this. Of course, you would verify at NIST.

[bob1029]

> a commercial consumer

Where does it say these are commercial consumers?

https://en.wikipedia.org/wiki/Schriever_Space_Force_Base#Rol...

> Building 400 at Schriever SFB is the main control point for the Global Positioning System (GPS).

[throw0101c]

> I've never heard of this! Very cool service, presumably for … quant / HFT / finance firms (maybe for compliance with FINRA Rule 4590 [3])?

To start with, probably for scientific stuff, à la:

* https://en.wikipedia.org/wiki/White_Rabbit_Project

But fibre-based time is important in case of GNSS time signal loss:

* https://www.gpsworld.com/china-finishing-high-precision-grou...

[esseph]

I'm sure all of that is true, but so is "Department of Defense".

They're also the largest holder of IPv4 space, still. https://bgp.he.net/report/peers#_ipv4addresses

[squigz]

Why does the DoD hold so many IPv4s?

[ignoramous]

> Google/hyperscalers as input to Spanner or other global databases?

Think Google might have rolled their own clock sources and corrections.

Ex: Sundial, https://www.usenix.org/conference/osdi20/presentation/li-yul... / https://storage.googleapis.com/gweb-research2023-media/pubto... (pdf)

[mmaunder]

SIGINT as a source clock for others in a network doing super accurate TDOA for example.

[anilakar]

But they do not need absolute time, and internal rubidium clocks can keep the required accuracy for a few days. After that, sync can be transferred with a portable plug, which is completely viable in tactical/operational level EW systems.

[secondcoming]

I think Google uses chrony instead of NTP

[creatonez]

Google doesn't use chrony specifically, just an algorithm that is somewhat chrony-like (but very different in other ways). It's called Google TrueTime.

[machinationu]

science equipment, distributed radio-telescopes where you need to precisely align data received at different locations