On 01/02/12 18:52, Chris Albertson wrote:
On Wed, Feb 1, 2012 at 9:20 AM, Bob Camp<[email protected]> wrote:
Hi
The "gotcha" with a public grandmaster is routing to it. Without 1588
routers / hubs / switches / what ever, the result is compromised. You fall
back into the same routing delay mess as NTP. Since public pretty much means
internet accessible, you would need to upgrade a lot of stuff. Since that
includes the traditional "last mile" gear, it's not a simple proposition at
all. At least in my case, I get more delay from the ends of most connections
than I get from all the routing in-between.
I think except for testing you need the grand master to live on your
own Ethernet. And I mean "Ethernet" in the most precise way. Two
Ethernets with a router between them is not an Ethernet it is two
Ethernets with a router. sub-uSec synchronization is very hard
over over any network if packets get stored and forwarded and that is
what routers do.
NTP is better if the network path is complex and you don't have
end-to-end control over all the equipment.
I think it's best to start from requirements rather then starting from
solutions. But if your requiremt is to get time to within a few uSec
and all the machines are in the same lab PTP can work.
Next you have to figure out some way to TEST is the machines are all
in fact in sync at the uSec level and if yu are using PTP the test
should not also use PTP. Testing, I think is the hardest part.
Do you want a plain Ethernet switch or a IEEE 1588 capable Ethernet
switch? Which PTP capable switch did you choose?
Cheers,
Magnus
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