[ntp:hackers] IEEE 1588 support in NTP?

Martin Burnicki martin.burnicki at meinberg.de
Fri Oct 28 03:41:30 PDT 2005


David,

Our company Meinberg is offering a NTP time server which also works as a PTP 
grandmaster clock with a built-in hardware time stamp unit. We've recently 
participated in the IEEE-1588 meeting in Winterthur near Zurich/Switzerland. 
Part of that meeting was a plug-fest where PTP capable devices from different 
manufacturers were interconnected in order to see that they could work 
together. For more information please see our news article:
http://www.meinberg.de/english/news/news_051015_001.htm

David D. Hagood wrote:
> Has any consideration been given to adding support for IEEE-1588
> Precision Time Protocol (PTP) into NTP?
>
> PTP (http://ieee1588.nist.gov/) is a standard for time synchronization
> over LAN for instrumentation - it is a part of the LAN extensions for
> Instrumentation (LXI - http://www.lxistandard.org/), and provides for
> time sync to tens of nanoseconds (YMMV - routers screw that up). The
> intended use is in a stack of instruments in a lab, connected to each
> other and to a PTP source via a local hub.
>
> The overall goals and methods of PTP are very much the same as NTP, and
> I'd hate to have to put both NTPD and PTPD
> (http://ptpd.sourceforge.net/) on the same machine as they would fight
> like cats and dogs over who was master - ideally you'd have one daemon
> doing both, and picking the "best" source.
>
> Where I work we are building gear that is Linux based (and so can have
> NTPD trivially) but I'd like to be fully LXI compliant which means
> supporting PTP as well (plus some of the stuff we do we need time sync
> to at worst hundreds of nanoseconds), and being a lazy cuss I'd rather
> see something like that in the mainstream NTPD rather than having to put
> it in myself on our own branch.

Please keep in mind that PTP yields an accuracy in the nanosecond range *only* 
if special network adapters with PTP support are used on all PTP nodes. 

PTP support for network adapters means that the adapters include a hardware 
timestamp unit which takes a time stamp whenever a PTP packet goes on the 
wire or is coming in from the wire. 

Without that hardware support PTP doesn't offer significantly more precision 
than NTP.


Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany


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