PTP (IEEE 1588) needs custom interface hardware, though. The Ethernet interface has added hardware to time stamp when the packet is sent/received, and that's what the software uses to do the precision measurements.
I suppose one could (try to) use PTP over a wireless link. That would take an even more exotic wireless interface that had the PTP measurement hardware built into the interface. I don't know that anyone is actually making such hardware. There are some papers that turn up in a search, but that's about it. I've tried to do something similar, using PC-ethernet-wireless AP :over the air: wireless AP-ethernet-PC, about 5 years ago, and it wasn't particularly great. But there, I'm pretty sure the limiting issue was that there wasn't any deterministic timing between the ethernet wired interface and the 802.11a wireless interface (that is, the boxes I was using were really wireless bridges and had internal storage) On 10/8/10 1:23 PM, "David N. Lombard" <[email protected]> wrote: On Fri, Oct 08, 2010 at 05:40:28AM -0700, Matt Hurd wrote: > > Know some guys here in Australia that are doing extremely accurate > timing with wireless, not for timing's sake but to measure movement in > dam walls and other infrastructure. Kind of like a localised GPS. > They have some very neat and accurate stuff. > > Had a play with some radio foo and managed to get about 880ns + air > time on bit to bit from tx to rx but haven't quite figured out how to > get super low latency yet. I think there may be a product in there > for wireless PPS dissemination for accurate timing to a cluster like > the guys do with the dam walls but I'm not sure if people really need > much more than what ptp can already do. Yes, PTP could enable fairly tight time sync across a cluster, if it were used. -- David N. Lombard, Intel, Irvine, CA I do not speak for Intel Corporation; all comments are strictly my own. _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
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