[time-nuts] Fw: Optical transfer of time and frequency

[Magnus Danielson]

Javier,

On 05/01/2016 02:54 PM, Javier Serrano wrote:
> On Sun, May 1, 2016 at 9:50 AM, Magnus Danielson
> <magnus at rubidium.dyndns.org> wrote:
>> If I recall correctly, there where some White Rabbit stuff available from
>> vendors, was it only Ethernet switches or also cards?
>
> Yes, the switch is available from two vendors that I know of. They are
> referenced at [1]. For nodes, we have a page describing what hardware
> support is needed [2]. Then there are various boards available
> commercially which implement that hardware support, like [3].
>
> For the particular case of WR-enabled TDCs, one could use the SPEC
> PCIe carrier [3] with a TDC FMC [4] or a simple DIO FMC [5],
> delegating then the TDC function to the FPGA on the carrier, using an
> HDL core like [6]. Or roll your own, of course.

Thanks for this listing!

> Has anybody experienced with free-space optical gigabit Ethernet
> links? I am curious about whether the transceivers have a fixed
> latency or at least a latency one can easily quantify online. This is
> the trickiest part for adding WR support on top of a given physical
> layer.

There exists optical links that is used to solve the "last mile" 
problems. I have not used any of those myself.

I also know that there is microwave links which essentially just 
converts the optical GE encoding onto a microwave carrier and back.
It could be an interesting option to consider.

Most of the microwave links that is in regular use however have modes 
that re-encode things and will break White Rabbit. It also breaks my 
stuff every once in a while, so I know more about these systems than I 
should know. My EFTF-2014 presentation and paper give some comments on it.

Cheers,
Magnus

> Cheers,
>
> Javier
>
> [1] http://www.ohwr.org/projects/white-rabbit/wiki/Switch#Commercial-producers
> [2] http://www.ohwr.org/projects/white-rabbit/wiki/WRReferenceDesign
> [3] http://www.ohwr.org/projects/spec/wiki
> [4] http://www.ohwr.org/projects/fmc-tdc/wiki
> [5] http://www.ohwr.org/projects/fmc-dio-5chttla/wiki
> [6] http://www.ohwr.org/projects/tdc-core/wiki
>