White rabbit is the version of IEEE1588 that locks bit clocks. Normal IEEE1588 doesn't do this. For this reason, (last I looked), there was no 10G implementation. 1G speeds is the highest White Rabbit implementation. The HW support for "normal" IEEE1588 is used to timestamp the packets without software in the loop (where the CPU will introduce jitter).
But you don't necessarily need any special HW for IEEE1588... it can all be done in a normal FPGA using the standard Xilinx 10G IP core. There are FPGA cores available for the IEEE1588 part, so you don't have to implement it yourself. We considered this for MeerKAT at one stage, but in the end we couldn't achieve the required performance. It might be quite workable for HERA, though. Anyway, just a thought. It'd save you buying special HW and running additional fibres, if it meets your performance targets. Jason Manley CBF Manager SKA-SA Cell: +27 82 662 7726 Work: +27 21 506 7300 On 05 May 2015, at 18:49, Dan Werthimer <d...@ssl.berkeley.edu> wrote: > > > hi dave, > > i also think distributing clock and 1 PPS is simpler than IEEE1588. > > some of the IEEE1588 and white rabbit experts are here at berkeley. > see for example: > http://chess.eecs.berkeley.edu/pubs/881/dreams.pdf > > my limited understanding is that 1588 phase locks the bit clocks of > routers and switches together. 1588 routers and switches have SMA > connectors on them so you can use external maser/rubidium/GPS references. > > you can achieve spectacular accuracy and stabilitity with white rabbit > if you employ really good oscillators at each node, > i think white rabbit can acheive 70 picosecond RMS time transfer. > > best, > > dan > > > > > > On Tue, May 5, 2015 at 8:52 AM, David MacMahon <dav...@astro.berkeley.edu> > wrote: > Hi, Jason, > > I have a great deal of curiosity about IEEE-1588, but I've always wondered > about the precision/stability that's attainable. Compared with multiple > sample clocks, correlating signals sampled with one common clock seems far > more forgiving vis a vis clock frequency/phase stability. If you or John > could point me to any information about this, please do! > > Thanks, > Dave > > On May 4, 2015, at 11:44 PM, Jason Manley wrote: > > > On the far end of the concept spectrum, have you considered distributing > > time over your existing ethernet network with IEEE-1588, and using this to > > discipline local ovenised 10MHz oscs at each antenna? > > > > I'm cc'ing Johan Burger, who heads up our Timing and Frequency Reference > > subsystem, who might be able to offer some additional insight. I know > > they've tried a few different lasers and detectors, with varying levels of > > success. > > > > Jason Manley > > CBF Manager > > SKA-SA > > > > Cell: +27 82 662 7726 > > Work: +27 21 506 7300 > > > > On 05 May 2015, at 5:18, Bob Stricklin <bstr...@n5brg.com> wrote: > > > >> Hi Jack and John, > >> > >> I wanted to add an input here….. > >> > >> I am working on a 10 MHz GPS slaved reference for my personal use. I am > >> working with a Analog Devices AD9548 Evaluation board (~$250) , GPS with 1 > >> PPS, and a ovenized 10 MHz osc. I also plan to distribute this clock and > >> have considered the Avago fiber product line. One of the older generation > >> Avago fiber parts should work fine for <$25 per channel. With careful > >> control of lengths and delays it should be possible to maintain good > >> phasing between channels. The analog devices chip is <$50 so a custom > >> solution should be <$500/reference but with considerable development time. > >> > >> Bob Stricklin > >> > >> > >>> On May 4, 2015, at 10:02 PM, Jack Hickish <jackhick...@gmail.com> wrote: > >>> > >>> Hi John, > >>> > >>> Thanks for the info. I'll add Litelink to my list of suppliers to > >>> investigate. > >>> We have no particular urge to multiplex the signals on to the fiber > >>> unless there's a particularly neat/cheap solution to do that. There's no > >>> great appetite to go custom. We've got about ~30 nodes, and my first stab > >>> at getting an off-the-shelf solution turned up at a few k$ / node, not > >>> including any cleanup electronics. > >>> > >>> Thanks again, > >>> > >>> Jack > >>> > >>> On Mon, 4 May 2015 at 19:25 John Ford <jf...@nrao.edu> wrote: > >>>> Hi CASPERites, > >>>> > >>>> For HERA, we're looking at distributing timing signals (PPS & 10Mhz ref > >>>> or > >>>> 500 MHz clock) over O(100m) fibers to various digitization nodes. > >>>> I figure some folks in CASPERland have experience with this kind of > >>>> system? > >>>> Did you use custom RF-over-fiber kit, or off-the-shelf PPS/10MHz > >>>> solutions? > >>>> Any words of wisdom/caution to share? > >>>> > >>>> Any responses much appreciated! > >>> > >>> We have several different schemes for the different signals. Are you > >>> planning for one fiber per signal per node? or one fiber with the signals > >>> multiplexed on them? > >>> > >>> If the signals are one per signal, you can use some off-the-shelf > >>> solutions, but they are kind of pricey, and if you have a lot of nodes to > >>> supply, it might be worth working on something custom. We have used Math > >>> Associates stuff for this kind of work. Math Associates is now litelink, > >>> and they tout the affordability of their stuff, so maybe it's > >>> reasonable... > >>> > >>> > >>> On the 10 MHz, we send the 10 MHz reference over fiber, and at the far end > >>> use a crystal oscillator locked to the reference to clean up the noise > >>> from the fiber electronics. This is essential for interferometry, but > >>> maybe not for single-dish use. > >>> > >>> John > >>> > >>>> > >>>> Jack > >>>> > >>> > >>> > >> > > > > > > >
