Re:Time Card and PTP on a Raspberry Pi Compute Module 4
by michaelt on Friday September 03, 2021 @09:46AM
(#28404168)
The most well known applications include:
* High-speed stock trading, where regulations often require precise timestamping.
* Cell phone networks, where adjacent towers have to hold their frequencies precisely, and synchronise their transmit and receive time windows to avoid interference.
* Certain types of distributed database [1]
At a broader level, guarantees/specifications about NTP accuracy are hard to find. If you google 'NTP accuracy' you'll find a very wide range of claims, from sub-millisecond to >1 second [2]
Indeed, a lot of the NTP userbase has timing requirements so lax they can 'smear' a leapsecond [3] over the course of 24 hours, tolerating a sustained error of hundreds of milliseconds. They've got good reasons for doing it - but it goes to show big errors are possible even under normal, correct operation.
Therefore, if you have an application that needs single-millisecond-level accuracy, you won't find an NTP product specification saying it's what you want.
* High-speed stock trading, where regulations often require precise timestamping.
* Cell phone networks, where adjacent towers have to hold their frequencies precisely, and synchronise their transmit and receive time windows to avoid interference.
* Certain types of distributed database [1]
At a broader level, guarantees/specifications about NTP accuracy are hard to find. If you google 'NTP accuracy' you'll find a very wide range of claims, from sub-millisecond to >1 second [2]
Indeed, a lot of the NTP userbase has timing requirements so lax they can 'smear' a leapsecond [3] over the course of 24 hours, tolerating a sustained error of hundreds of milliseconds. They've got good reasons for doing it - but it goes to show big errors are possible even under normal, correct operation.
Therefore, if you have an application that needs single-millisecond-level accuracy, you won't find an NTP product specification saying it's what you want.
[1] https://en.wikipedia.org/wiki/Spanner_(database)#Architectur... [2] http://www.ntp.org/ntpfaq/NTP-s-algo.htm#Q-ACCURATE-CLOCK [3] https://developers.google.com/time/smear