e-vlbi at ≥ 1 gbps -- “unlimited” networks? tasso tzioumis australia telescope national...
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e-VLBI at ≥ 1 Gbps --“unlimited” networks?
Tasso Tzioumis
Australia Telescope National Facility (ATNF)
4 November 2008
Introduction
• Very Long Baseline Interferometry (VLBI)• Combining (correlating) very distant radio telescopes
• “virtual” large telescope more resolution == detail
• “Baseline” = distance 100s-1000s km• Interferometry = pair-wise correlation• Telescopes widely distributed over countries, continents,
even in space.• Traditionally: “record” data on tapes or disks & “correlate”
later (days or weeks or months)
• e-VLBI• Real-time VLBI using fast network transfers into hardware
or software correlators
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LBA Radio Telescopes in AustraliaLBA Radio Telescopes in Australia
x Katherine
x New Norciax Yarragadee
x ASKAP
x
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VLBI Astronomy Arrays (c. 2008)
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O New telescopes in last decade
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Resolution (==Details)
Resolution = Observing wavelength / Telescope diameterAngularResolution
Optical (5000A)Diameter Instrument
Radio (4cm)Diameter Instrument
1′ 2mm Eye 140m GBT+1″ 10cm Amateur Telescope 8km VLA-B0.″05 2m HST 160km MERLIN0.″001 100m Interferometer 8200km VLBI
Jupiter and Io as seen from Earth1 arcmin 1 arcsec 0.05 arcsec 0.001 arcsec
Simulated with Galileo photo
Atmosphere gives 1" limit without corrections which are easiest in radio
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Cen A
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Sensitivity
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HST Deep Field
• Observe weak objects• Look into different populations
• e.g. Hubble Deep Field• View much older objects Look back in time
• New insights into universe
• Need similar sensitivity in the radio spectrum
Radio Telescope sensitivity
• Sensitivity depends on:• Size of the telescope - very expensive to increase• Radio receivers – limit of state of the art electronics
• Cryogenically cooled to liquid He temperatures
• Integration time – limited by clock stability• ** Bandwidth Data rate (after sampling)
• Most cost effective to achieve!?• Most progress in recent years• >1 Gbps routinely achieved
• VLBI data on disks• High data rates expensive to support
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e-VLBI – real-time observing over fast networks
• e-VLBI• Transport the VLBI data over fast networks for “real-
time” operation fast response• Data rates at 1 Gbps or more are required• BUT very expensive commercially
Collaboration with network providers• National Research and Education Networks (NREN)• E.g. Internet2; DANTE collaboration; AARNet
• Research in Astronomy & Networking• Very high and sustainable datarates (> 12 hours) • Testing the speed and reliability of the networks
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e-VLBI Challenges - 1
• “last-mile” fibre connectivity• Connect remote telescopes to the NREN backbone• Fibre build needed - expensive• But many institutions already at 1 Gbps
• Tools and protocols• Sustained high rate traffic required• TCP/IP needs “fine tuning” to achieve high rates
• Congestion control can create problems
• Other protocols needed (UDP; modified TCP & UDP…)• Research and development needed
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e-VLBI Challenges - 2
• Long intercontinental distances• RTT Australia-Europe > 300 ms• Routed Ethernet not consistently reliable• Dedicated “light-paths” at 1 Gbps
• Can be “built” over ethernet backbone• Require NREN cooperation over many countries
• e.g. 3 x 1 Gbps Oz-Holland in 2007
• Real-time data processing • Hardware correlators – new interfaces• Software correlators – new developments
• Supercomputer clusters and “grid” applications
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e-VLBI Achievemnts - EXPReS project connectivity world-wide
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Oz achievements
• Telescope connectivity at 2 x 1 Gbps• $2M fibre to telescopes built by CSIRO • University fast connections in Uni Tasmania, Swinburne
(Melbourne) & Curtin (Perth)• 1 Gbps operation demonstrated within Australia
• 512 Mbps “production” e-VLBI
• 512 Mbps operation with Europe (12 hours) in 2007• 512 Mbps operation with Japan and China in 2008• Internet2 IDEA award - 10 Gbps link in US for 1 year• New fibre-build for new telescope (ASKAP) in WA
• Construction to commence shortly• Research for next generation radio astronomy instruments ( e.g.
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Image created by Paul BovenSatellite image: Blue Marble Next Generation, courtesy of NASA Visibible EarthNOBUGS November 2008
Next steps
• 10 Gbps connectivity• NREN backbones already at 10 Gbps• Multiple colours possible (many λλ on one fibre)
• Dynamic circuit allocations• Build light-paths and other circuits interactively• Systems in test
• Distributed correlation• “grid-like” applications• Flexible operations on software
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Lessons learned
1. NREN collaboration critical• Must involve networking community• Symbiotic relationship – science + networks
2. Network tools development• Tools and protocols need development• Sustained high data rates over long distances still
problematic “light-paths”
3. Very high data rates are achievable now• Almost “infinite” data pipes• NREN test circuits at low cost• e.g. AARNet “try-before-you-buy” scheme
• 6-12 months free 1 Gbps+ connectivity!
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“Paradigm shift” – “unlimited” networks??
• Current way of science planning• Current plans often limited by scarce network resources• Researchers assume connectivity the limiting factor• Often limit our own visions and horizons
New way of planning?• Plan on the science needs assuming almost “infinite”
networks!!• Fast research networks are arriving very quickly• Expand our horizons now!
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Contact UsPhone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Thank you
ATNFTasso TzioumisLBA & eVLBI
Phone: +61 2 9372 4350Email: [email protected]: www.atnf.csiro.au/vlbi
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