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. Fiber delays are evaluated using a two-way scheme, and used in phase shifters to produce accurate PPS pulses everywhere. Our first Ethernet switch prototype proved the concept works, although we are far from a final system covering all our specs, and now we are thinking about making this a more serious project by applying for EU funding. In the proposal document there is a very important chapter on "Impact" and I would be very interested in reading about potential applications you might have for such a network. Here is our list so far:
- Synchronization of different parts of large experimental physics facilities (the original purpose). The advantage wrt current approaches is you could do both data and timing on the same fiber. I am not saying nobody has done timing over Ethernet so far, we have done our homework and none of the existing projects fulfilled our constraints concerning clock quality, accuracy, number of nodes, distances, Ethernet compliance and "transparency", latency, determinism, design openness, etc. - Distributed data acquisition: you can have ADCs feeding data to rolling buffers, and all connected to this White Rabbit (WR) network. When one of them receives a trigger we want to produce the effect in the control room that all of them were triggered at the same time. So the trigger pulse gets a precise UTC time tag and then all the other ADCs are informed of it (through the same network) and also requested to freeze their buffers and return the appropriate subset of data (again through WR) for coherent display on operational consoles. The 1 ns spec comes mainly from this type of application, applied to analog signal acquisition in particle accelerators. Other examples are distributed sound measurements, structural monitoring (vibration), power monitoring (detection of partial discharge and dielectric losses in high voltage power cables: by taking synchronized measurements over a segment of cable, defects can be pinpointed and repaired before complete failure of the transmission line occurs), distributed RF Time Division Multiple Access (TDMA) and meteorological event measurements (e.g. lightning). - Backbone for wireless positioning networks. There are projects to build wireless networks in factories where you can position a mobile wireless node by measuring two-way delays wrt fixed wireless points, which need to be very well synchronized among themselves. I am very interested in hearing about any potential application you could imagine for White Rabbit, and also of course about any remarks on the project in general. Cheers, Javier _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.