Javier Serrano wrote:
Dear nuts,
We have this ongoing project whose aim is to synchronize roughly one
thousand stations (typical distances around 10 km) to within 1 ns using
Ethernet:
http://www.ohwr.org/twiki/bin/view/OHR/WhiteRabbit/WhiteRabbit
The idea is basically to use Synchronous Ethernet and something PTP-like in
combination. Sync Ethernet means from a timing point of view there is
hierarchy: there is a master source and its frequency is used to encode data
in the uppermost Ethernet switch in the hierarchy. This frequency then
propagates everywhere because switches extract it off the incoming data on
their "uplink" port and use it to encode data on every "downlink" port.
There is several types of "Synchronous Ethernet", but here is one where
the bit-clock is being steered just as in a SDH network, and infact this
variant is also supported in modern G.781 synchronisation.
The other form possible is by using counters and interchanging values.
Ah well.
Synchronous Ethernet that steers bitclock will be tainted by
inter-symbol interference, but it is not too bad for most purposes.
I have a thick WhiteRabbit document to read in detail, but other things
have come inbetween.
Cheers,
Magnus
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