[ntp:questions] Re: IEEE 1588 support in NTP?
martin.burnicki at meinberg.de
Mon Oct 31 09:40:38 UTC 2005
David L. Mills wrote:
> I have seen the 1588 document. I hear newsflash from your competitor
> Syummetricom on the same issues. However, affordable PTP interface
> devices will need to be available for various networks (10/100/1000
> Ethernets, FDDI, etc.) for the technology to propser.
However, whereas (AFAIK) the roots of NTP lie in computers, Unix
workstations, etc., 1588 comes from the industrial automation sector.
There are lots of companies who manufacture specialized devices which have
used special communication techniques in the past. Now more and more of
them use standard Ethernet networking technology.
Since those devices are often not just standard PCs but special hardware
devices, the developers of those devices can easily provide a network
interface which supports hardware timestaming for PTP packets.
> While 1588 provides a precision timestamp, it doesn't say what to do
> with them to discipline the system clock, if that is required. The NTP
> clock discipline algorithm might be a good candidate for that. This is
> not a trivial algorithm, along with kernel support, but would be
> necessary if the overhead of frequent PTP exchanges becomes a problem.
Agreed. Also, NTP also has improved concepts of redundancy, security, etc.,
what is still missing in PTP. However, the PTP standardization groups are
working on that.
> An interesting project would be to write a driver for the PTP device
> that passes the timestamps and data on to NTP and modifiy the protocol
> module to use them. This needs to be done carefully, as the I/O cacheing
> on Solaris, for example, seems to be ever increasing.
In fact we have already done some first tests where we use PTP timestamps
> I suspect your product, like the Symetricom product, includes both 1588
> and NTP. I would assume also that 1588 could serve as a reference clock
> for NTP and possibly the other way around, like for instance to
> synchronize time among 1588 islands.
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