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221 points mfiguiere | 4 comments | | HN request time: 0.614s | source
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throw0101a ◴[] No.33696297[source]
So they state:

> One could argue that we don’t really need PTP for that. NTP will do just fine. Well, we thought that too. But experiments we ran comparing our state-of-the-art NTP implementation and an early version of PTP showed a roughly 100x performance difference:

While I'm not necessarily against more accuracy/precision, what problems specifically are experiencing? They do mention some use cases of course:

> There are several additional use cases, including event tracing, cache invalidation, privacy violation detection improvements, latency compensation in the metaverse, and simultaneous execution in AI, many of which will greatly reduce hardware capacity requirements. This will keep us busy for years ahead.

But given that NTP (either ntpd or chrony) tends to give me an estimated error of around (tens of) 1e-6 seconds, and PTP can get down to 1e-9 seconds, I'm not sure how many data centre applications need that level of accuracy.

> We believe PTP will become the standard for keeping time in computer networks in the coming decades.

Given the special hardware needed for the grand master clock to get down to nanosecond time scales, I'm doubtful this will be used in most data centres of most corporate networks. Adm. Grace Hopper elegantly illustrates 'how long' a nanosecond is:

* https://www.youtube.com/watch?v=9eyFDBPk4Yw

How many things need to worry the latency of signal travelling ~300mm?

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1. stingraycharles ◴[] No.33702897[source]
> But given that NTP (either ntpd or chrony) tends to give me an estimated error of around (tens of) 1e-6 seconds, and PTP can get down to 1e-9 seconds, I'm not sure how many data centre applications need that level of accuracy.

I know that in trading, auditing trades / order books requires extremely accurate timing, and they typically deploy GPS hardware to get the required level of accuracy. As GPS is accurate to a level of 30ns, 1e-6 to 1e-9 (1ns) is exactly the kind of improvement needed to not need GPS hardware anymore.

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2. throw0101a ◴[] No.33705582[source]
> […] improvement needed to not need GPS hardware anymore.

You're simply trading NTP hardware for PTP hardware (grandmaster clocks). There is no way to get to 1e-9 scales without hardware support.

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3. bradknowles ◴[] No.33716078[source]
A good Stratum-1 GNSS from a company like Meinberg or Microchip will include a Rubidium or Cesium reference clock that is then disciplined by GPS and can get you down to sub-nanosecond level accuracy.
4. bradknowles ◴[] No.33716086[source]
These days, all the vendors I know of are shipping hardware that does both. So, it's not just an NTP server, it's also a PTP server. Maybe you don't use one or the other part of that functionality, or maybe they are licensed separately, but they are there.