Re: [Linuxptp-users] One PCs with multiple NICs acting as multiple PTP master / PTP chains

[Richard C. <ric...@gm...>]

On Fri, Feb 21, 2014 at 01:16:09PM +0000, Koehrer Mathias (ETAS/ESW5) wrote:
> Hi all,
> 
> to synchronize a couple (6-8) PCs I want to use one PCs PTP master and the others as PTP slaves.
> To interconnect the PCs I can use a PTP capable switch. However these switches are fairly expensive.
> The first question I have: How does a "standard" Ethernet switch perform? Which accuracy will be possible if no other traffic is running over the switch but PTP packets?

The answer is, it depends.

It depends on the switch itself and the amount of traffic through the
switch. Usually switches add something like 10 microseconds delay and
a few microseconds jitter.

I would definitely try this first and just see what kind of RMS
numbers come out.


> As PC 1 ... PC 7 have two PTP clocks running, these clocks have to be synchronized.
> Is this done via phc2sys? If yes, do I have to synchronize directly from PTPx to PTPy or does it work via the PCs System clock?

You can use phc2sys to synchronize the PHC clock pairs. However, this
will be a PITA to set up, and remember, unless you feed signals from
one card to the next, you will be using a kind of software time
stamping. Chaining those servos together accumulates the errors.

I would guess that the normal switch would perform much better. Try
the switch idea first.

HTH,
Richard