On 25 January 2012 09:04, Bob Dunlop <bob.dunlop@???> wrote:
> Hi,
>
> On Tue, Jan 24 at 06:15, James Courtier-Dutton wrote:
>> Does anyone have experience of both ntp and ptp ?
>
> Use NTP all the time and am planning to move to PTP for some deployments
> in the near future. What are your actual requirements ? As we have to
> keep telling our customers. "Tell us what you want to do, not how you
> think it can be done."
>
>
> NTP on a quiet LAN is good for ~100us maybe down into the tens of us. If
> WAN links are involved then think milliseconds, might be better to just
> sync each station to GPS.
>
> Software PTP won't give you much better running on non realtime systems
> such as linux. With software PTP just about any decent switch that
> supports multi-cast will be fine.
>
> Hardware PTP where the NIC does timestamping of the packets at capture or
> transmission is better, you should easily be able to go sub microsecond but
> have you thought about other factors ? PC processor clocks are rubbish,
> you won't be able to maintain a stable reference without something like a
> temperate compensated crystal. Also beyond two or three systems on a LAN
> this is when you'll need proper PTP support in network switches etc, what
> that really means is they run PTP internally and act a secondary clocks
> for the attached devices. Back to the start, why would you need this
> accuracy ?
>
>
> Our customers are getting us to push the boundry on syncronisation of data
> timestamps between stations. Next generation systems will have TXCO for
> internal clocks, hardware PTP support in the NICs etc. Precision costs.
>
My requirement is more of an experiment really.
I would like to have ethernet connected speakers. (with a mini PC
between ethernet and speaker)
So, if you have two speakers that are separated, each being fed by the
TCP/IP stream, can you get one mini PC to process the Left speaker
sound, and the other mini PC to process the right speaker sound.
Currently, to get the output of the two speakers synchronized, I would
need each mini-PC to be well time synced together.
I don't think NTP has the accuracy needed. The trouble is that sound
moves quite quickly, so the accuracy of the samples being sent to the
sound card has to be surprisingly good.
If you expand the system to 7.1, the time sync problem is vital.
So long as I can get the mini-PC system clock accurate, the inaccuracy
of the sound card clock can be corrected.
This same synchronization could make for much cheaper video walls etc.
although bizarrely, timing of video is not so vital due to artifacts
of perception.
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