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High Rate Internet Data Transfer for eVLBI

High Rate Internet Data Transfer for eVLBI. Ralph Spencer, Richard Hughes-Jones and Simon Casey The University of Manchester All Hands Sept 2005. Radio Astronomy. The study of celestial objects at <1 mm to >1m wavelength. Sensitivity for continuum sources

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High Rate Internet Data Transfer for eVLBI

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  1. High Rate Internet Data Transfer for eVLBI Ralph Spencer, Richard Hughes-Jones and Simon Casey The University of Manchester All Hands Sept 2005

  2. Radio Astronomy • The study of celestial objects at <1 mm to >1m wavelength. • Sensitivity for continuum sources • B=bandwidth, t=integration time. • High resolution achieved by interferometers. Some radio emitting X-ray binary stars in our own galaxy: GRS 1915+105 MERLIN Cygnus X-1 VLBA SS433 MERLIN and European VLBI

  3. GRS 1915+105: 15 solar mass BH in an X-ray binary: MERLIN observations receding 600 mas = 6000 A.U. at 10 kpc

  4. Very Long Baseline Interferometry

  5. D q Dcosq X How interferometry works • Interferometer: signals from each telescope brought together coherently for correlation (multiplication) • Resolution l/D << that possible from a single telescope, e.g the pimples on a golf ball at 3000 miles at the highest resolution • Output of the correlator is one component of the Fourier transform of the sky brightness

  6. Earth-Rotation Synthesis The baseline between each pair of telescopes forms an ellipse as the Earth rotates .

  7. The Aperture Plane (u,v) EVN • Need ~ 12 hours for full synthesis, not necessarily collecting data for all that time. • Telescope data correlated in pairs: N(N-1)/2 baselines • NBTrade-off between B and t for sensitivity ~sqrt(Bt) • Data are calibrated, Fourier inverted and then deconvolved to give the images. MERLIN

  8. The European VLBI NetworkEVN • Detailed radio imaging uses antenna networks over 100s-1000s km • At faintest levels, sky teems with galaxies being formed • Currently use disk recording at 512Mb/s (MkV) • real-time connection allows greater • response • reliability • sensitivity • Need Internet eVLBI

  9. EVN-NREN Gbit link Chalmers University of Technology, Gothenburg OnsalaSweden Gbit link TorunPoland Jodrell BankUK WesterborkNetherlands DedicatedGbit link MERLIN Dwingeloo DWDM link CambridgeUK MedicinaItaly

  10. eVLBI Milestones • January 2004: Disk buffered eVLBI session: • Three telescopes at 128Mb/s for first eVLBI image • On – Wb fringes at 256Mb/s • April 2004: Three-telescope, real-time eVLBI session. • Fringes at 64Mb/s • First real-time EVN image - 32Mb/s. • September 2004: Four telescope real-time eVLBI • Fringes to Torun and Arecibo • First EVN, eVLBI Science session • January 2005: First “dedicated light-path” eVLBI • Australia to JIVE via Canarie: data from Huygens descent transferred at ~450Mb/s

  11. 20 December 20 2004 • connection of JBO to Manchester by 2 x 1 GE • eVLBI tests between Poland Sweden UK and Netherlands at 256 Mb/s • February 2005 • TCP and UDP memory – memory tests at rates up to 450 Mb/s (TCP) and 650 Mb/s (UDP) • Tests showed inconsistencies between Red Hat kernels, rates of 128 Mb/s only obtained on 10 Feb • Haystack (US) – Onsala (Sweden) runs at 256 Mb/s • Regular tests with VLBI data every ~6 weeks • 128 Mpbs OK, 256 Mpbs often, • But not 512 Mbps – WHY NOT? • Correlator can cope with large error rates • up to 2 % • but need high throughput for sensitivity • implications for protocols

  12. UDP Throughput Oct-Nov 2003 Manchester-Dwingeloo Production • Throughput vs packet spacing • Manchester: 2.0G Hz Xeon • Dwingeloo: 1.2 GHz PIII • Near wire rate, 950 Mbps • UDPmon • Packet loss • CPU Kernel Load sender • CPU Kernel Load receiver • 4th Year project • Adam Mathews • Steve O’Toole

  13. January 2005 repeated UDP over 2 days

  14. ESLEA • Packet loss will cause low throughput in TCP/IP • Congestion will result in routers drooping packets: use Switched Light Paths! • Tests with MB-NG network Jan- • JBO connected to JIVE via UKLight in June (thanks to John Graham, UKERNA) • Comparison tests between UKLight connections JBO-JIVE and production (SJ4-Geant)

  15. UKLight Switched light path

  16. Tests on the UKLight switched light-path Manchester : Dwingeloo • Throughput as a function of inter-packet spacing • Packet loss • Maximum size packets can reach full line rates with no loss, and there was no re-ordering (plot not shown).

  17. Tests on the production network Manchester : Dwingeloo. • Throughput • Small (0.2%) packet loss was seen • Re-ordering of packets was significant

  18. UKLight using MkV terminals

  19. The GÉANT2 Launch June 2005

  20. Dwingeloo DWDM link Jodrell BankUK MedicinaItaly TorunPoland e-VLBI at the GÉANT2 Launch Jun 2005

  21. UDP Performance: 3 Flows on GÉANT • Throughput:5 Hour run 1500 byte MTU • Jodrell: JIVE2.0 GHz dual Xeon – 2.4 GHz dual Xeon670-840 Mbit/s • Medicina (Bologna):JIVE 800 MHz PIII – Mk5 (623)1.2 GHz PIII330 Mbit/s limited by sending PC • Torun:JIVE 2.4 GHz dual Xeon – Mk5 (575)1.2 GHz PIII245-325 Mbit/s limited by security policing (>600Mbit/s  20 Mbit/s) ? • Throughput:50 min period • Period is ~17 min

  22. 18 Hour Flows on UKLightJodrell – JIVE, 26 June 2005 • Throughput: • Jodrell: JIVE2.4 GHz dual Xeon – 2.4 GHz dual Xeon960-980 Mbit/s • Traffic through SURFnet • Packet Loss • Only 3 groups with 10-150 lost packets each • No packets lost the rest of the time • Packet re-ordering • None

  23. Conclusion and Future directions • eVLBI needs to get to rates of 512 Mpbs – not there yet. • Rates of 256 Mpbs on production networks possible now using TCP/IP in good conditions, but not higher rates. • G2 launch showed continuous long term flows as in VLBI have different characteristics to those in short term tests (Iperf, UDPmon) : more investigation needed – collaborating with DANTE and SURFnet • Packet loss is a killer for TCP – new protocols needed (ESLEA) - VSI-E standard • The End Host Problem • The performance of Motherboards, NICs, RAID controllers and Disks matter: Mk V units (Conduant) • MkV-B 2 Gbps data recording in 2 yrs? • Next generation correlator 10 Gbps in 5-10 yrs

  24. Thanks to • Paul Burgess JBO • Steve Parsley, Arpad Szomoru, Cormac Reynolds JIVE • Nicola Pezzi, John Graham, Colin Greenwood, Peter Clarke ESLEA • EVN observatories staff

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