Graham: Synchronizing Clocks by Leveraging Local Clock Properties (2022) [pdf] • Hacker News Board

Re: Graham: Synchronizing Clocks by Leveraging Local Clock Properties (2022) [pdf]

#11

Post by hermitdev » Mon, Aug 11, 2025, 2:14 PM UTC

RossBencina wrote: post #6

bux93 wrote: post #4

Earlier quoted context omitted.

The paper mentions TCXOs and OCXOs, respectively temperature and oven-controlled crystal oscillator. You can get PCIe cards that have these on them, and devices for audio studios with a rubidium oscillator like the Tascam CG-1800. Jane Street has a podcast that lifts the veil a little bit on how they keep their gear synced up, which is pretty interesting: https://signalsandthreads.com/clock-synchronization/

The Jane Street podcast was a very approachable explanation, and was interesting to me for a few reasons: (1) that EU regulation requires their timestamps to be within 100 microseconds of UTC, and (2) they claim to achieve 20 microsecond accuracy using hardware-timestamped NTP synched to local NTP time servers, the NTP servers then being synced to off-the-shelf GPS masters using PTP, (3) they really didn't like the i…

> that EU regulation requires their timestamps to be within 100 microseconds of UTC,

It's the same in the US. It's covered under CAT NMS (Consolidated Audit Trail, National Market System). Probably too much information at: https://www.catnmsplan.com/

Re: Graham: Synchronizing Clocks by Leveraging Local Clock Properties (2022) [pdf]

#12

Post by adrian_b » Mon, Aug 11, 2025, 2:27 PM UTC

bux93 wrote: post #4

RossBencina wrote: post #3

I wonder whether there are clock generators with on-chip temperature sensing... Yes: "an advanced, low-power, high-performance mobile clock generator with four clock outputs. The device integrates a MEMS resonator, temperature sensor and a temperature-to-digital converter (TDC), which eliminates the need for external crystal and temperature-sensing crystal resonators." -- https://www.sitime.com/products/clock-generat…

The paper mentions TCXOs and OCXOs, respectively temperature and oven-controlled crystal oscillator. You can get PCIe cards that have these on them, and devices for audio studios with a rubidium oscillator like the Tascam CG-1800. Jane Street has a podcast that lifts the veil a little bit on how they keep their gear synced up, which is pretty interesting: https://signalsandthreads.com/clock-synchronization/

Nitpick: the C in TCXO stands for "Compensated", not for "Controlled", like in OCXO.

That means that the resonator of an OCXO is held at a constant temperature, while that of a TCXO is at the ambient temperature, but the temperature is monitored and a compensation circuit adjusts the resonance frequency, maintaining it as constant as possible.

Re: Graham: Synchronizing Clocks by Leveraging Local Clock Properties (2022) [pdf]

#13

Post by jeffbee » Mon, Aug 11, 2025, 2:38 PM UTC

hermitdev wrote: post #11

RossBencina wrote: post #6

Earlier quoted context omitted.

The Jane Street podcast was a very approachable explanation, and was interesting to me for a few reasons: (1) that EU regulation requires their timestamps to be within 100 microseconds of UTC, and (2) they claim to achieve 20 microsecond accuracy using hardware-timestamped NTP synched to local NTP time servers, the NTP servers then being synced to off-the-shelf GPS masters using PTP, (3) they really didn't like the i…

> that EU regulation requires their timestamps to be within 100 microseconds of UTC, It's the same in the US. It's covered under CAT NMS (Consolidated Audit Trail, National Market System). Probably too much information at: https://www.catnmsplan.com/

Yes, and the fact that this has been a global regulation for years suggests that it isn't all that special. Outfits like Goldman Sachs meet this regulation with fewer blogs.

Re: Graham: Synchronizing Clocks by Leveraging Local Clock Properties (2022) [pdf]

#14

Post by adrian_b » Mon, Aug 11, 2025, 2:42 PM UTC

RossBencina wrote: post #5

bux93 wrote: post #4

Earlier quoted context omitted.

The paper mentions TCXOs and OCXOs, respectively temperature and oven-controlled crystal oscillator. You can get PCIe cards that have these on them, and devices for audio studios with a rubidium oscillator like the Tascam CG-1800. Jane Street has a podcast that lifts the veil a little bit on how they keep their gear synced up, which is pretty interesting: https://signalsandthreads.com/clock-synchronization/

The CG-1800 uses "a high-precision OCXO (oven-controlled crystal oscillator)" https://tascam.com/us/product/cg-1800/ only mention of rubidium is: "An external input connector that supports a 10MHz signal enables the CG-1800 to be connected to a rubidium clock or GPS clock for even higher precision." On the other hand, Antelope Audio 10MX is a rubidium word clock source: https://en.antelopeaudio.com/products/10mx/ Sur…

Cheap second hand rubidium frequency standards may be worthwhile, unlike new rubidium oscillators, which are not that good in comparison with good OCXOs to make their much higher price acceptable.

Traditional rubidium frequency standards still have an aging rate that is high enough to be non-negligible. While from the datasheet of a rubidium oscillator it appears that it is better than an OCXO, that can be misleading, because many OCXOs have very predictable aging drifts. If you compensate the aging in software, you may reach a similar performance to a rubidium oscillator.

In recent years there have been invented several new kinds of rubidium frequency standards, with much better performances than the traditional models. However these are either not available yet as commercial products or they may have a single provider which demands a steep price.