Yes, exchanging data over a link will always harm its timing accuracy/precision performance, irrespective of whether you steer clocks (our case) or you exchange values or both. In fact, as I said to Jeremy in another thread I tend to see clock steering (i.e. PLL) as a limit case of interchanging values, where this exchange would happen at every single clock tick. So you end up with lots more information, up to you to low-pass filter to get rid of high frequency phase noise.
Cheers, Javier On Fri, Sep 11, 2009 at 12:30 AM, Magnus Danielson < [email protected]> wrote: > 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 > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
