... | ... | @@ -35,6 +35,85 @@ USB port (up to v. 3.2 switches) or the "FPGA test" USB port in the rear |
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(newer switches). RS232 parameters are 115200,
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8N1.
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### Q: Is it possible to use White Rabbit systems in different locations and be able to have synchronised time via Satellite link?
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Basically as long as the 10 MHz and PPS that you give to the different
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White Rabbit systems are synchronised, WR will keep its promises.
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For example, you may synchronise two WR networks by at both ends letting
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a GPS generate the PPS and 10MHz signals, but you will be limited by the
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precision the GPS will give you on those two different locations. This
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may be as good as 3 ns already or maybe better in combination with
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augmentation systems.
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Or you can synchronise your systems much later, as CERN has done with
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the CNGS experiment where we could, *after the fact*, synchronise
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related events happening on both sites (whe sent neutrinos through the
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earth's crust). The article [Time transfer techniques for the
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synchronisation between CERN and
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LNGS](https://www.ohwr.org/documents/112) explains this.
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If you have Satellite links, you can use Two-Way Satellite Time Transfer
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(TWSTT) and have on both sides a system that will provide the PPS and 10
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MHz signals. According to the presentation [Time transfer through
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optical
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fibers](http://www.ptb.de/emrp/1393.html?&no_cache=1&cid=2274&did=2820&sechash=9d1ec729),
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page 3 from Mrs. Amy-Klein from LPL, Paris, you can have an accuracy
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better than 1 ns.
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Using Time Transfer by Laser Link (T2L2) would give you even a sub-ns
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accuracy.
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The [NEAT-FT Workshop on Optical Networks for Accurate Time and
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Frequency Transfer](http://www.ptb.de/emrp/1393.html) held in 2012 may
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give you more ideas and you possibly can find partner institutes that
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can help you with such a
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system.
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-----
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## Inter-operability
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### Q: Is the WR Switch inter-operable with standard PTP (IEEE1588-2008) gear ?
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A: Yes, although you would completely loose the sub-ns timing resolution
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of White Rabbit, a WR switch is interoperable with PTP and it has been
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tested for inter-operability on ISCPS PlugFest, but
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- currently, WR devices (Switch/nodes) do not support standard-PTP
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slave mode. This means that a standard PTP device can "slave" to WR
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device (being master) but a WR device cannot slave to standard PTP
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device (WR device cannot be standard PTP-slave)
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- it is important to remember that WR devices use a very specific PTP
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configuration (2-step, delay request-response mechanism, multicast,
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Layer 2) which is not the most popular configuration and it is not
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the default setting for standard-PTP devices (which use IP instead
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of Layer 2). So it is not just plug\&play, it's more like
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1\. buy PTP switch which supports fully the standard
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2\. configure it properly (change from IP to Layer 2)
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3\. plug &
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play
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### Q: Can you have a different vendor switch between it and another white rabbit device to distribute the time? Around a larger network for instance?
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A: No, you cannot do this and still expect to have the sub-ns timing
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resolution of White Rabbit. If the switch between the WR master (switch)
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and the WR end node is a standard PTP one, your timing resolution will
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be reduced to the relatively low PTP precision. The reason is that the
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White Rabbit protocol works on each link and there is no end-to-end
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synchronisation.
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If you want to build a larger distance network, you may want to know
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that there are several meteorological institutes working on extending
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the 10 km range. One may replace the standard SFP's by longer distance
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ones (see [Non-compliant SFP types](/Non-compliantSFP)), and there may
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be ways of multiplexing specific wavelengths on a dark channel in a
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Telecom network. Also light amplifiers may be used. See for example the
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data of *Vrije Universiteit Amsterdam and VSL* at [Users of WR
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technology](/WRUsers). At the moment of writing (April 2013) no links
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longer than 16 km have been made though.
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The [NEAT-FT Workshop on Optical Networks for Accurate Time and
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Frequency Transfer held in 2012](http://www.ptb.de/emrp/1393.html) may
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give you more ideas and you possibly can find partner institutes that
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can help you with such a
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system.
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-----
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## General questions
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... | ... | @@ -59,30 +138,7 @@ project](https://www.ohwr.org/project/wr-switch-hw) one can find the |
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### Q: Does the switch comply to CE regulations (EMC)?
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A: It is. The company Seven Solutions has performed extensive EMC tests
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on the
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switch.
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-----
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## Inter-operability
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### Q: Is the WR Switch inter-operable with standard PTP (IEEE1588-2008) gear ?
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A: Yes, it is and it has been tested for inter-operability on ISCPS
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PlugFest, but
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- currently, WR devices (Switch/nodes) do not support standard-PTP
|
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slave mode. This means that a standard PTP device can "slave" to WR
|
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device (being master) but a WR device cannot slave to standard PTP
|
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device (WR device cannot be standard PTP-slave)
|
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- it is important to remember that WR devices use a very specific PTP
|
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configuration (2-step, delay request-response mechanism, multicast,
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Layer 2) which is not the most popular configuration and it is not
|
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the default setting for standard-PTP devices (which use IP instead
|
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of Layer 2). So it is not just plug\&play, it's more like
|
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|
1\. buy PTP switch which supports fully the standard
|
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2\. configure it properly (change from IP to Layer 2)
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3\. plug & play
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on the switch.
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-----
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... | ... | |