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Comment by hummo56 | Hacker News Reader

Interesting project, especially to gain insights into the FPGA programming part.

I think it is essentially a mixture of PTP and NTP now.

I guess this will work within the same local network, as the major inaccuracy of NTP comes from the asymmetric path delays at the network layer over the Internet.

PTP solves this by incorporating these hardware timestamps exactly. But this works only within the same LAN.

Here is an interesting PTP core:

https://github.com/freecores/ha1588

Yes it is "old" but that is typically fine with HW projects.

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The main difference between PTP and NTP is that PTP relies on hardware support in switches and routers. Those are not cheap. If they had the same support for NTP, it would perform as well.

A highly accurate stratum-1 NTP server can be build with a common computer NIC. No need to mess with FPGAs (unless that's your thing). The Intel I210 is about $50. It has a PPS input and output. With some calibration, the timestamping can be accurate to few tens of nanoseconds.

NTP can work very well between directly connected NICs. But without hardware support in the switches/routers, that accuracy degrades quickly in the network. A single switch can easily add hundreds of nanoseconds worth of jitter and tens of nanoseconds worth of asymmetry.

PTP at this point is ubiquitous and cheap. It is hard to source a PHY that has no support for it in 2021.

> If they had the same support for NTP, it would perform as well.

Unless you'd extend NTP to become PTP, it absolutely wouldn't.

Yes, NICs with support for hardware timestamping are common (it's typically in the MAC, not PHY), but switches that have a good support for PTP, either as a boundary clock, or transparent clock, are not cheap. At least I have not seen one yet. Do you have any examples?

Some switches support NTP as a server and client (equivalent to the PTP boundary clock), but there don't seem to be any using hardware timestamping. It's just the classic ntpd using software timestamps, good to few tens of microseconds at best.

And yes, NTP could definitely perform as well as PTP if the switches had a proper support. In my tests with directly connected NICs the synchronization is stable to few nanoseconds, same as with PTP. At the protocol level, they use the same timestamps.

> Do you have any examples?

Probably all current Cisco offerings? Ubiquiti industrial switches? A whole crowd of second tier vendors like Lantech or Korenix? These are just those I had direct experience with.

Of these, Cisco definitely does boundary clock on L3, on at least several models of their routers.

> In my tests with directly connected NICs the synchronization is stable to few nanoseconds, same as with PTP.

Yes network sync is piece of cake if you drop the whole network bit. That said am slightly skeptical about ns level precision with NTP. Did you measure synchronicity between the two devices via scope?

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